BOILER
What is the meaning of marine boilers ?
Boiler is a pressure vessel used on ships in which the water is heated to evaporate and generate the steam and the unit is so arranged that the generated steam accumulated in it. The two main types are water tube and fire tube.
What is the boiler mounting ?
It is directly fitted to the boiler shell. They are:
Safety valve
Main steam stop valve
Air vent cock
Two gauge glass level indicators
Feed check valve
Scum blow down valve
Bottom blow down valve
Salinity cock or test cock
Man hole doors.
Where are air vent cock located and its purpose ?
The air vent cock is fitted at the top of the steam space of the boiler.
Its purpose are-
To release air from the boiler either filling the boiler water or raising the steam.
To allow air to enter in the event of boiler cooling down or blowing down. ( to prevent vacuum effect)
What are the safety arrangements in marine boiler ?
Safety valve
Low / high water level alarm
Too low water level alarm and shut down
Water level indicators
Pressure gauge
Low fuel oil pressure alarm
Low / high fuel oil temperature alarm
Flame failure alarm
Smoke density alarm
Easy gear arrangement
Air vent
Force draught fan stop alarm
Low / high steam pressure alarm
Why need to blow down the gauge glass ?
Gauge glass blow down is made to know the boiler and gauge glass connection is clear or not and to give the exact water level in the boiler.
Boiler gauge glass blow through procedure ?
Shut steam and water cocks than open the drain cock.
After draining water from the sight glass, there is nothing come out, both steam and water cocks are good in order.
Open the steam cock side, blow out the steam.
Close the steam cock side, the steam connection is clear.
Open the water cock side, blow out the water.
Close the water cock side, the water connection is clear.
Close the drain cock.
Open the water cock, water should then gradually come rise up to the top of the gauge glass.
Open the steam cock, the water in the glass should fall to the level of the water in the boiler.
Why need to blow down the boiler water ?
Boiler blow down is made to reduce the density of salt and to remove the dissolved and suspended solids, also the floating solid impurities in the boiler system.
If there are not removed from the boiler water system, foaming, priming, corrosion will occur in the boiler steam space and feed water system.
See ‘Boiler Blow Down’.
Why scum blow down or surface blow down is carried out ?
To remove accumulated, suspended and floating solids, impurities and also remove dissolved solid concentration, they hinder the formation of steam.
Why bottom blow down is carried out ?
To remove suspended solids and residual sludge that have settled at the bottom.
If these contaminants are not removed regularly they will build up until they hinder the circulation patterns.
What is the purpose of boiler water test ?
To ensure that proper chemical treatment are maintained at all time.
To detect the present of contaminants in the water that may be injurious to boiler and system.
Enumerate the boiler water test ?
Alkalinity test [Phenolphthalein ( p) alkalinity test, Total ( T ) alkalinity test (2 x P)]
Chloride test
Condensate PH test
Amerzine test ( Hydrazine test )
Excess phosphate test
Conductivity test (Total dissolve solids test)
Hardness test
Alkalinity test
This is to ensure that the boiler water prevent corrosion by neutralization of acidic gases.
(a) Phenolphthalein or ‘p’ alkalinity
This test is carried out to prevent acidic corrosion
To test for presence of all of the hydroxide, one half of the carbonate and one third of phosphate present in a water sample.
(b) Total ( T ) alkalinity test
To determine the amount all of hydroxide, all of the carbonate, and two thirds of the phosphates
Note: Hydroxides and carbonates can co-exist together in a solution but hydroxides and bi-carbonates cannot.
Chloride test
To know the amount of salt in boiler water.
To minimize chloride level and to adjust the blow down.
Condensate PH test
To control condensate PH value within a limit.
To minimize corrosion in steam and condensate system.
Amerzine test ( Hydrazine test )
To test for dissolved Oxygen content
To know reserve hydrazine (N2H4 ) ppm and to prevent corrosion and aeration.
To minimize oxygen pitting and corrosion in boiler, steam and condensate system.
Phosphate test
To control the scale formation due to hardness (presence of Phosphate in sample means no hardness salts)
A reserve of phosphate should be maintained in the boiler water ready to neutralize any hardness salts which may enter.
Conductivity test
Measure of the total amount of dissolved solids (T.D.S) including the treatment chemicals. (Excessive density leads to priming and or deposits)
To remove dissolved and suspended solid by blowing down.
Hardness test
To check for salt causing “hardness”
Note: Hardness test of boiler water are not necessary when the phosphate is above the lower limit of the control range.
What are the advantages of boiler water treatment ?
To prevent the scale formation in the boiler and feed system
To prevent corrosion in boiler and feed system.
To control the sludge formation and prevention of carry over with the steam.
To maintain the boiler water in alkaline condition and free from dissolved gases.
To prevent of entry into the boiler of foreign matter such as oil, waste, mill scale, FeO, Cu, Sand, etc.
Exhaust gas boiler (EGB or EGE) or economiser described in this article is a smoke tube boiler with steam space, used for heat recovery from main engine exhaust gas. An illustration of the boiler is shown in figure below. The exhaust gas boiler is designed as a vertical boiler with a cylindrical shell surrounding the boiler tubes and water drum as well as the steam space. The tubes consist of a large number of smoke tubes and a small number of stay tubes. The stay tubes with an increased diameter act as support for the boiler. Both types are welded onto the lower and upper tube plates. The steam space is formed by the shell plate and internal cone. At the top it is closed by means of the end plate.
October 12, 2015 8:30 pm | 1 Comment | Frozee
What is foaming in auxiliary boilers and how to prevent it ?
It is the formation of thick layer of steam bubbles on the top of the water surface inside the boiler due to:
High concentration of impurities.
By the animal or vegetable fats in feed water carry over from the oil heaters.
Increase in level of dissolved & suspended solid TDS level.
Increase in water level.
To prevent foaming, surface or scum blow down should done frequently to expel any floating impurities for the boiler and no lube oil should be allowed to enter the boiler.
What is boiler priming and how to prevent it ?
It is condition in which large amount of water are carried along with the steam into the steam line. It is caused by:
Excessive foaming
Improper amount of steam space
By a sudden rush of steam such as is produced when steam stop valve is suddenly opened.
To prevent priming, never keep the water level too high. Open steam stop valve slowly.
What action do you made take in case of foaming and priming ?
Scum blow down
Reduce boiler fire rate
Check whether boiler chemical added are in excess
Detect the source of contamination
In case of bad priming the boiler may have to be taken out of service, shut down.
Note: For contamination due to oil, auxiliary boiler have to be chemically cleaned.
What is the boiler cool down procedure ?
Change the fuel oil burning system from HO to DO and then shut down the burning system.
Stop feed p/p close feed check valve.
Drain down the boiler after allowing it to cool down.
If no sufficient time to do this, lower the boiler pressure to 3 to 4 bar.
Shut the main steam stop valve.
Open the ship side valve then open the blow down valve.
Banging noise will appear when boiler is empty.
Close the boiler blow down valve and ship side valve.
Then release the steam pressure through safety v/v by means of easing gear.
When pressure is off, open the air vent and the boiler to cool down.
Boiler Opening up and Inspection Procedure
Follow as procedure above, after making sure no vacuum in it, first:
To remove top man hole door, slacken the dog holding nuts but do not remove them until first broken the joint
Remove nuts and dogs and take out the door.
The bottom door can be removed after warning personnel to keep clear of the top door.
Make ventilation before entering. Do not allow naked light near the boiler.
Preliminary internal inspection carried out before cleaning, to check scale deposits and any special points.
Plug orifice to blow down valve to prevent choke, place guards over the manholes landings to prevent damage.
Carried out cleaning and internal works.
When all works completed, a full internal examination must be carried out
Cleanliness, all openings are clear, water level gauge connection clears from deposits
All internal pipes and fittings have been replaced correctly and securely attached,
Remove plug from the blow down valve orifice
The face of manhole doors and landings inspect to clean and undamaged.
Replace manhole doors by using new joints.
Operate all boiler mountings. Open air vent cock and fill the boiler with water to sufficient level.
Describe the boiler start up procedure from cool condition ?
The boiler is carried out firing from cold condition to normal working pressure condition very slowly to avoid thermal stress.
Check the boiler blow down valve in close position.
Shut the main steam stop v/v.
Open the air vent cocks.
Open the feed check valve and pumping up to ¼ of gauge glass level.
Start the force draft fan with dampers, open correctly to purge the furnace and combustion space of any foul gas.
Light the burner after closing the recirculating valve.
Normally allow the fire to burn for 5-minutes and stop for 15 mins. This step continues until steam come out.
When steam coming out from the air vent close the air vent (at 1 to 2 bar pressure).
Rise up the working pressure step by step slowly. (Allow the fire to burn for 30 mins and stop the fire for 10 min.)
When the steam pressure reached is working pressure drain the steam line. (to avoid water hammer)
Main steam stop valve open slowly (crack opening)
How to take action if gauge glass showing low water level ?
If water level has not yet dropped completely out the sight glass, water may be put into the boiler.
If water drops completely out of sight glass, check another sight glass, if both disappear water; do not add water until the boiler is cool enough to prevent any possible damage due to rapid cooling of over heated plate.
The fire must be immediately stopped.
The main steam stop valve must be closed.
Blow down and cool down the boiler.
Check leakage, drum outside, Located the cause of trouble and make necessary repair.
Enter the boiler after it has cooled and examined any possible damage.
After repair, water fill up slowly and restore to normal operation.
If no damage occurred, inject the water slowly into the boiler and restore it to operation.
What are the causes if gauge glass shows low water level ?
One gauge glass defective
Boiler tube crack and leaking
Feed water regulator jammed
Failure of feed water pump (Air in feed water line or pump)
Level controller malfunction
Steam consumption is too much
What is caustic embrittlement? How to prevent it ?
It is inter crystalline fracture. It is cause by high concentration of caustic soda and the material under stress. The stress corrosion cracks follow the grain or crystal boundaries of the material and failure.
Sodium sulphate or sodium nitrate is used for the prevention of caustic embrittlement.
It can be found in highly stress area in boiler. Such as tube and tube plate connection, riveted head, seam and boiler mountings.
What is foaming in auxiliary boilers and how to prevent it ?
It is the formation of thick layer of steam bubbles on the top of the water surface inside the boiler due to:
High concentration of impurities.
By the animal or vegetable fats in feed water carry over from the oil heaters.
Increase in level of dissolved & suspended solid TDS level.
Increase in water level.
To prevent foaming, surface or scum blow down should done frequently to expel any floating impurities for the boiler and no lube oil should be allowed to enter the boiler.
What is boiler priming and how to prevent it ?
It is condition in which large amount of water are carried along with the steam into the steam line. It is caused by:
Excessive foaming
Improper amount of steam space
By a sudden rush of steam such as is produced when steam stop valve is suddenly opened.
To prevent priming, never keep the water level too high. Open steam stop valve slowly.
What action do you made take in case of foaming and priming ?
Scum blow down
Reduce boiler fire rate
Check whether boiler chemical added are in excess
Detect the source of contamination
In case of bad priming the boiler may have to be taken out of service, shut down.
Note: For contamination due to oil, auxiliary boiler have to be chemically cleaned.
What is the boiler cool down procedure ?
Change the fuel oil burning system from HO to DO and then shut down the burning system.
Stop feed p/p close feed check valve.
Drain down the boiler after allowing it to cool down.
If no sufficient time to do this, lower the boiler pressure to 3 to 4 bar.
Shut the main steam stop valve.
Open the ship side valve then open the blow down valve.
Banging noise will appear when boiler is empty.
Close the boiler blow down valve and ship side valve.
Then release the steam pressure through safety v/v by means of easing gear.
When pressure is off, open the air vent and the boiler to cool down.
Boiler Opening up and Inspection Procedure
Follow as procedure above, after making sure no vacuum in it, first:
To remove top man hole door, slacken the dog holding nuts but do not remove them until first broken the joint
Remove nuts and dogs and take out the door.
The bottom door can be removed after warning personnel to keep clear of the top door.
Make ventilation before entering. Do not allow naked light near the boiler.
Preliminary internal inspection carried out before cleaning, to check scale deposits and any special points.
Plug orifice to blow down valve to prevent choke, place guards over the manholes landings to prevent damage.
Carried out cleaning and internal works.
When all works completed, a full internal examination must be carried out
Cleanliness, all openings are clear, water level gauge connection clears from deposits
All internal pipes and fittings have been replaced correctly and securely attached,
Remove plug from the blow down valve orifice
The face of manhole doors and landings inspect to clean and undamaged.
Replace manhole doors by using new joints.
Operate all boiler mountings. Open air vent cock and fill the boiler with water to sufficient level.
Describe the boiler start up procedure from cool condition ?
The boiler is carried out firing from cold condition to normal working pressure condition very slowly to avoid thermal stress.
Check the boiler blow down valve in close position.
Shut the main steam stop v/v.
Open the air vent cocks.
Open the feed check valve and pumping up to ¼ of gauge glass level.
Start the force draft fan with dampers, open correctly to purge the furnace and combustion space of any foul gas.
Light the burner after closing the recirculating valve.
Normally allow the fire to burn for 5-minutes and stop for 15 mins. This step continues until steam come out.
When steam coming out from the air vent close the air vent (at 1 to 2 bar pressure).
Rise up the working pressure step by step slowly. (Allow the fire to burn for 30 mins and stop the fire for 10 min.)
When the steam pressure reached is working pressure drain the steam line. (to avoid water hammer)
Main steam stop valve open slowly (crack opening)
How to take action if gauge glass showing low water level ?
If water level has not yet dropped completely out the sight glass, water may be put into the boiler.
If water drops completely out of sight glass, check another sight glass, if both disappear water; do not add water until the boiler is cool enough to prevent any possible damage due to rapid cooling of over heated plate.
The fire must be immediately stopped.
The main steam stop valve must be closed.
Blow down and cool down the boiler.
Check leakage, drum outside, Located the cause of trouble and make necessary repair.
Enter the boiler after it has cooled and examined any possible damage.
After repair, water fill up slowly and restore to normal operation.
If no damage occurred, inject the water slowly into the boiler and restore it to operation.
What are the causes if gauge glass shows low water level ?
One gauge glass defective
Boiler tube crack and leaking
Feed water regulator jammed
Failure of feed water pump (Air in feed water line or pump)
Level controller malfunction
Steam consumption is too much
What is caustic embrittlement? How to prevent it ?
It is inter crystalline fracture. It is cause by high concentration of caustic soda and the material under stress. The stress corrosion cracks follow the grain or crystal boundaries of the material and failure.
Sodium sulphate or sodium nitrate is used for the prevention of caustic embrittlement.
It can be found in highly stress area in boiler. Such as tube and tube plate connection, riveted head, seam and boiler mountings.
In the exhaust gas boiler tubes, heat from the main engine exhaust gas is transferred to the water side by convection. On the water side, the heat is transferred by evaporation of the saturated water adjacent to the tubes where steam bubbles are formed. As the steam bubbles have a much lower specific density than the water, they will rise rapidly to the steam space where water and steam are separated. The steam space of the boiler is designed to absorb the shrink and swell volumes. It is advisable, however, to avoid sudden and large load variations as this might create instability in the steam system, and cause level alarms.
As the pressure part is made of mild carbon steel with elevated temperature properties stress concentrations in corner welding are minimised. In emergency mode the exhaust gas boiler can therefore be operated with low water level and even without water with the full exhaust gas flow through the boiler tubes, provided the boiler is operated depressurised and the inside temperature does not exceed 400˚C.
For inside inspection, the boiler is arranged with both hand holes and manholes. Two manholes are arranged at the bottom end of the boiler shell for convenient access into the water drum. For visual check of the smoke tubes and steam space, a number of hand holes are arranged in a suitable distance at the bottom and top of the boiler shell.
The boiler foundation consists of four foundation consoles giving the necessary support and absorption of the thermal expansion.
Finally, the heating surface dimensions of the boiler are designed to maintain a sufficient exhaust gas velocity giving the best self-cleaning effect within the design limits. However, after long term operation soot deposits can be accumulated inside the boiler tubes. The heating surface of the boiler can be cleaned easily by means of water washing or by adding soot remover into the exhaust gas flow using compressed air.
When the boiler is started, the lighten-up rate of the boiler must not be accelerated too much as this might cause an unnecessary over strain of the boiler material by quick and uneven temperature rises. It might be necessary to perform a number of start/stop sequences to reduce the lighten-up rate.
At the commissioning start-up of the boiler and after any repair work of the refractory, it is very important to further reduce the lighting-up rate. This is because the new refractory still contains a small amount of water. When heated the water vaporises and expands which might cause fissures and cracks in the refractory. The burner must therefore only be operated at minimum load and in intervals of 1-2 minutes for the first hours. Between each operation interval the burner should remain stopped for approximately 8-10 minutes. The article explains starting and stopping boiler during normal and emergency working conditions.
Precautions on Starting Boiler
Before start-up of the boiler plant, following general work and check procedures must be considered.
Check that the main steam valve, by-pass valve and circulation valves if provided, scum valve, and blow-down valves are closed.
Open the feed water valves and the air valve. Fill the boiler with feed water to approximately 50 mm below normal water level. The water level rises due to expansion when the boiler is heated. If the temperature difference between the boiler and feed water exceeds approximately 50ºC, the boiler must be filled very slowly.
When filling a pressure less boiler, the shut-off valve after the feed water pump must be throttled. Otherwise the pump motor will be overloaded.
Check the water level in the water level gauges. Check frequently during the complete start-up. The water level gauges should be blown down several times to ensure a correct indication.
Check that the water level control system is connected and operational.
Check the oil system and start the fuel oil supply pump. Pre-heat the fuel oil if the burner should operate on heavy fuel oil.
Check the burner and the safety functions according to the manufacturer instruction.
Starting Boiler and Pressure Rise
The following work procedures must be followed during start-up of the boiler.
Check that the gauge board valve and pressure gauge valves are opened.
Check that the air valve is open if the boiler pressure is below 1.0 bar.
Start the burner on manual control and on low load. Check that the water level does not rise too high during the pressure rising period.
Drain via the blow down valves if the water level is too high.
If the air valve was opened close it when only steam blows out. A pressure reading should be indicated on the boiler pressure gauge before the air valve is closed.
Tighten all covers such as manholes, hand holes, inspection doors, etc. during the pressure rising period. If required, check all flange joints on the plant.
Change to automatic control of the burner when the boiler pressure is 0.5 bar lower than the working pressure of the boiler.
Open the by-pass valve slowly to heat-up and pressurise the steam system. If the boiler is not provided with a by-pass valve, the main steam valve should be used to heat-up and pressurise the steam system.
Open the main steam valve and close the by-pass valve.
Open the valves to the steam consumers carefully in order to avoid water chocks.
When the boiler is in normal operation, check that the water level control system and the gauge board functions are fully operational.
After 3-4 weeks in operation, mud and deposits in the piping system may have accumulated in the boiler water. This may cause level variations which disturb the steam generation, and it is therefore recommended to blow down the boiler. It should then be inspected, cleaned, and refilled with boiler water.
Stopping Boiler
Normal boiler shut down
If necessary, the boiler can be shut down at any load without special preparations.
When the boiler is stopped, sudden temperature and pressure drops should be avoided as they might expose mountings, pipe lines, and the boiler plant to inadmissible temperature gradients.
When minimum load is obtained, stop the burner.
Keep the water level at normal level until the boiler stops producing steam.
Stop the feed water pump and close the feed water valves.
Close the main steam valve.
Emergency shut down
The boiler must be taken out of service immediately if parts of the heating surface have been glowing or the boiler shows recognisable deformations.
The supervising authorities must be informed, and the boiler must not be used until approval from these authorities is available a substantial loss of water is noted the feed water system is unable to provide the necessary amount of feed water, e.g. due to failure of parts the safety valve cannot function sudden cracks or damage are noted in the refractory, and if steam or moisture is coming out of the refractory oil in the feed water is detected too high salinity level is detected.
If an emergency shut down must be carried out, the fuel supply should be stopped. The main steam valve should be closed gradually, and the boiler must be cooled. The safety valves must not be operated. Parallel working boilers should be disconnected at once.
Stop for repair or inspection
The following describes the measures to be taken when the boiler is shut down for repair or inspection.
Clean the boiler from soot with water.
Operate the burner for at least 15 minutes after the soot removal to dry out the remaining water.
Stop the boiler as mentioned previously.
Check the furnace and the pin tubes with regard to cleanliness.
Empty the boiler from water and clean it. Check if lime stone appears.
Check and clean the outer fittings. Change gaskets where required.
Clean the feed water tank and feed water pipes.
Clean and grease the bearings of motor, pump, and fan.
Check and align the burner, if necessary.
If the boiler is shut down for a long period of time, the pin tubes must be thoroughly cleaned.
Check that the necessary spare parts are available. Order complementary parts in time.
It is of extreme importance that the boiler is NOT operated without water when the oil burner is in operation, e.g. due to disconnection of the water level safety devices. This will immediately cause complete break down of the boiler.
There is a number of ways to produce good quality feed water for boiler plants. Methods such as e.g. reverse osmosis plants or ion exchange plants produce good quality distillate. Also evaporators generally produce good distillate. The important thing is that the distillate used should be clean and without foreign salt contamination.
In practice most distillates used contain minor parts of various salt combinations which can and must be chemically treated away. Furthermore, the distillate may contain dissolved gases like for example oxygen (O2) and carbon dioxide (CO2) which may lead to corrosion in the boiler, steam, and condensate system.
Boiler and feed water must be chemically treated in order to avoid corrosion and scaling in the boiler.
The following text regarding feed and boiler water treatment is the normal recommendations for boilers with working pressure below 20 bars. These recommendations should be followed strictly in order to have the best working conditions for the boiler plant and to extend the working life of the plant. The requirements/recommendations of the various values for feed and boiler water are listed in Table 1 below.
Requirements for feed and boiler water
Unit
Feed water
Boiler water
Appearance
–
Clear and free of mud
Clear and free of mud
Hardness
ppm CaCO3
0 – 5
–
Chloride content
ppm Cl–
<15
<100
“P” alkalinity
ppm CaCO3
–
100 – 150
Total (T) alkalinity
ppm CaCO3
–
<2 x “P” – Alkalinity
PH-value at 25°C
–
8.5 – 9.5
10.5 – 11.5
Hydrazine excess
ppm N2H4
–
0.1 – 0.2
Phosphate excess
ppm PO4
–
20 – 50
Specific density at 20°C
Kg/m3
–
<1.003
Conductivity at 25°C
mS/cm
–
<2000
Oil content
–
NIL
NIL
If hydrazine (N2H4) is not used, sodium sulphate (Na2SO4) can be used instead, and the excess should be 30 – 60 ppm.
In cases where other kinds of oxygen binding agents are used, it is recommended that an excess of oxygen binding agents can be measured and indicates that no oxygen has been dissolved in the boiler water.
If it is requested to measure the content of dissolved oxygen directly, it is recommended to keep the value < 0.02 ppm.
In addition to the above values, the various water treatment companies will add further demands, depending on the method used for treatment of feed and boiler water.
However, the most important point is that the above values or their equivalents are observed and that a regular (daily) test of feed and boiler water is carried out.
Feed and Boiler Water Maintenance
The following are recommended water maintenance instructions. More exact details concerning analyses and blow downs should be set up together with the supplier of chemicals for water treatment.
Daily
Analyses of feed and boiler water.
Weekly
Skimming (surface blow down) according to analyses, but at least once per week (2 minutes with fully open valve).
Blow down (bottom blow down) according to analyses, but at least once per week (each blow down valve 1 minute in low load condition).
Monthly
Check the functions for salinity and oil detection systems.
Every six months
The boiler water side (interior) must be carefully inspected at least twice a year.
Yearly
Check of the water side of the boiler and hotwell/deaerator for corrosion and scaling.
Check the chemical pump unit.
The following is a brief description of the most important items of the boiler mountings. The components mentioned in this section are referring to the general arrangement drawing of the boiler.
Safety valves
Two safety valves are fitted to the pressure vessel of the boiler. They are installed for security reasons, and designed to prevent the boiler pressure from rising above the design value.
The safety valves must be supplied with waste steam pipes and either expansion devices, or bellows.
Main steam valve
The main steam valve is a shut off valve. When closed, it isolates the boiler from the main steam line. A check valve is mounted after the main steam valve which prevents steam from flowing backwards into the boiler.
The steam piping up to the main steam valve must be flexible in order to minimise external loads on the main steam valve and associated branch. The flexibility can be achieved with loops build into the main steam line to take up heat expansion from the boiler and steam piping or with an expansion joint next to or close to the main steam valve.
By-pass valve
The by-pass valve is a shut off valve. The purpose of the valve is to equalise the pressure between the boiler and the steam system when the main steam valve is closed. Please note that the by-pass valve is only supplied for larger boilers.
Feed water valve / feed valve (SDNR)
Two groups of feed water valves are provided in the boiler. Each group comprises a shut-off valve and a non-return valve. The shut-off valve in the ordinary group must be open when the boiler is in operation, or if the boiler is used as a steam drum. The shut-off valves should be closed when the boiler is not in use.
Water level gauges
Two local water level gauges are connected to the front of the boiler, each gauge being provided with two shut-off valves and a drain valve. The shut-off valves, fitted at the top and bottom of the sight glass, have a quick-closing mechanism to be used in case of broken glass. The pipes from the drain cocks on the water level gauge must lead to an open drain, visible for inspection.
Blow-down valve
Two blow-down valves are mounted at the bottom of the boiler body. If connected to a separate drainage system the valves are of the ball type. When connected to a common drainage system two valves are provided in each group, one shut-off valve and one shut-off/non-return valve. The shut-off function is for security and the non-return function prevents steam/water from flowing into an empty boiler by mistake.
Air valve
The air/ventilation valve located on top of the boiler is a shut-off valve. It is normally closed except when the boiler is being filled or completely drained. The end of the drain pipe from the air valve must be visible in order to determine when water or steam is coming out.
Scum valve
The scum valve is mounted at the top of the boiler body. In the event of scum in the boiler, this scum can be blown off from the water surface by opening this valve. If connected to a separate drainage system the valve is of the ball type. When connected to a common drainage system two valves are provided, one shut-off valve and one shut-off/non-return valve.
Sample valve
A sample valve is installed enabling connection to a sample cooler for taking test samples to perform boiler water analyses.
Inspection hole
Two small inspection holes are provided in the furnace wall to enable inspection of the burner flame. A proportion of the air supply is bled off from the burner fan to cool the window of the inspection hole, and prevent soot deposits.
Manhole
Two manholes placed at the boiler top and boiler bottom allow inside inspection of the steam/water drum.
Access doors
Access to the furnace and smoke outlet box are possible through the access doors placed at the bottom of the furnace and at the smoke outlet box respectively. Both access doors enable inspection of the generating tube bank.
Drain for furnace
The furnace bottom is provided with a socket for drain of the washing water.
The vertical two drum water tube boiler used normally on ships is top-fired and equipped with a steam atomising burner. As the burner, the local control panel and all relevant boiler mountings are mounted on top of the boiler, this can easily be operated and monitored from the burner platform.
The principal drawing of a typical auxiliary boiler is shown in figure below. The steam drum is cylindrical with two flat plates of equal thickness. Because of the internal pressure, the flat plates are mutually connected by vertical solid stays. The steam drum is furnished with the necessary internal fittings to ensure an even distribution of the feed water, of the circulation water from the exhaust boiler and to ensure a sufficient dryness of steam.
The burner cone in the furnace opening are an integrated part and accordingly no refractory are provided in the top of the furnace room. Manholes are conveniently placed in both drums and inside the drums enough space is available for inspection and maintenance. The water drum is designed similar to the steam drum. The drum size gives optimal space for the heating coil and easy access for inspection.
As standard the auxiliary boiler is prepared for tack welding along the foundation of the boiler shell. Some boilers may, however, be provided with four support feet instead, one as fixed foot and the others with the possibility of thermal expansion.
Both the furnace and the generating tube bank are located asymmetrically and are separated by the screen wall. Besides the screen wall the furnace consists of gas tight polygon shaped membrane walls. The generating tube bank consists of vertical pin-tubes arranged in a staggered configuration. To avoid any risk of vibration problems supports are arranged.
The flue gas passes through the deflected tubes at the bottom of the screen wall, up through the generating tube bank and out through the smoke outlet box. An effective circulation in the boiler is achieved bye means of down comers. The bottom tube plate is first covered with coat of insulation refractory and above with castable refractory. Access to the furnace is possible through the access door at the bottom of the furnace. Inspection of the generating tubes is also possible through the inspection door at the bottom of the furnace.
Inspection of the burner flame is possible through the two inspection holes arranged in two heights on the furnace panel wall.
Boiler Back Fire Incident on Ships
Outline:
Vessel was at anchorage awaiting berthing instructions.
18:00hrs – Fire in engine room reported to the bridge.
18:01hrs – Alarm sounded and announcement made on vessel PA system.
18:03hrs – All mustered at fire station and all are accounted for, several explosion’s were being heard coming from the engine room.
18:04hrs – Emergency stop for engine room operated, Quick closing valves operated & commenced boundary cooling.
18:05hrs ~ 1820hrs – Fire fighting team unable to enter engine room due to heavy smoke and continuous sound explosion.
18:30hrs – Explosion sound stopped, fire fighting team enter the engine room and fire extinguished using portable dry chemical extinguisher.
18:45hrs – Fire extinguished and confirmed no chance of re-ignition.
18:50hrs – Started cleaning the effected area and surrounding and assessing damage.
Damage:
Burner head assembly damaged due to boiler back fire
Air damper, fuel oil solenoid damaged
Ignition transformer and cables damaged
Flame eye detector and cables damaged.
Oil heater element, pressure gauge and thermometer damaged
Air blower motor.
Engine room fittings surrounding boiler front discolored.
Root Cause:
There have flashback incidents on board ships fitted with composite boiler in the past.
The manufacturers have issued a safety bulletin for this type of boiler which was not known to the office or Ship Staff.
As per the manufacturer’s recommendation, the burner can be changed to avoid a boiler back fire but this was not know to either the office/ship staff.
Contributory Cause:
The un-burnt fuel accumulated in the hot furnace lead to generation of a rich combustible mixture of air and fuel which was not completely purged during the pre-purge cycle prior to next start sequence. This caused boiler back fire in the furnace during re-igniting of the burner.
Although the exact cause of accumulation of un-burnt fuel in furnace has not been determined it is suspected that leaky fuel oil solenoid valve which lead to dripping of fuel oil in furnace after auto cut-off of boiler.
The boiler fuel oil solenoid valve had been opened up a number of times in the past as it was found leaking and was being overhauled by lapping the v/v disc and seat as no spare was available. The vessel did not inform the office on the condition of the valve.
Preventive action:
Safety bulletin issued for that type burner is included in the report.
For vessels fitted with the this type burner the Safety bulletin should be posted in the ECR and should be part of the engine room familiarization.
The makers have recommended modification to the burner which will be done on this burner.
Ch-Engineers of these vessels should include in their hand over notes the problem associated with this type of burner and refer to the safety bulletin.
Check through “peep hole” if ignition electrodes are giving spark for pilot burner and pilot burner is igniting and giving stable flame.
Check the funnel smoke which must be “dull black”. Black or white smoke indicates improper combustion of fuel with un-burnt fuel accumulating in the furnace.
Prior inspection of boiler burner or attempting to re-ignite the boiler burner after a flame failure alarm:
Change boiler control to manual, run the purge cycle for at least 5 minutes ensuring the blower damper is fully “open” position to ensure combustible gases purged out of furnace.
Check through peep hole for any hot spots near the burner area or furnace floor during purging.
Check funnel, must be clear of any smoke.
After above operation satisfactorily done, the maintenance on boiler can be carried out. Maker’s maintenance procedures during overhauling / repairing are to be adhered to at all times.
Lesson Learnt:
Duty engineer to check the burner flame (through peep hole) and the funnel smoke regularly during watch keeping and ensure proper combustion of fuel in furnace.
Regular maintenance of boiler fuel oil system components to be carried out as per maker’s instructions and at a specified interval or earlier if required.
Fuel oil system solenoid valves to be checked at regular intervals for positive shut off and must to be replaced if found leaking.
Do not attempt try to re-ignite the boiler burner without eliminating the cause of ignition failure.
What are the types of boiler by pressure ?
Low pressure boiler – up to 10Kg / Cm2
Medium pressure boiler – 10-25 Kg /Cm2
High pressure boiler – Over 25 Kg / Cm2
What is water hammering and how will you prevent it ?
It is the impact of moving water in steam line when the steam is allowed to enter a line with condensed water.
The steam will condenses and partial vacuum occurred and move back the water the along the pipe with very high velocity, and the water will strike at the vent or valves.
To prevent the water hummer –
Install steam trap in the line
Open the drain first before allowing the steam into the line.
Crack open of steam valve at first.
How to make boiler water test on your ship ?
The boiler test is carried out as follows.
Firstly take the boiler water sample from the salinometer cock or test cock and cool down.
The test is carried out by the using maker’s supply test kit, chemicals, instruments and instructions.
How do you take boiler water sample ?
Slowly open the salinometer cock until clean hot water coming out.
Then collect the boiler sample with copper jar.
How to know scum blow down valve open or not ?
It can be check by opening of ship side blow down valve. Banging noise will appear, scum blow down valve is in open position.
It can also detect, over heating of scum blow down pipe.
Where is manhole doors fitted ?
They are fitted at one at steam side and other one for water side.
Effect of foaming and priming ?
Can cause water hummer
Can cause contamination and scaling.
Can cause fluctuation of working water level.
What is boiler blow back ?
It occurs when lighting up with explosive gas and oil droplet (Oil residue) inside the furnace without pre-purging sufficiently.
The ignition results in a large flue gas inside the furnace and these gases blow out with increase high pressure through the furnace opening.
Procedure for hydraulic pressure test on marine boilers ?
Hydraulic pressure test is 1.25 times working pressure, ( 10 minutes maintain )
Close all openings.
Open air vent cock.
Fill up boiler water fully
Close the air vent cock
Place hydraulic jack to feed water line.
Fit standard pressure gauge.
Applied hydraulic pressure 1.25 times of working pressure and maintain 10minutes.
What is liquid coagulant in marine boilers ?
It has more molecular weight, colorless solution, containing sodium aluminates, starch, terming, and resin.
Once being dose into the boiler water floating solid particles and suspended solid are settled to the bottom of the boiler and easily remove by blowing down.
How to renew the boiler gauge glass ?
Shut steam and water cocks and open drain cock.
Check any leakage from the respective cock.
Slacken the gland nuts.
Open the cap and remove gauge glass.
Fit new gauge glass, correct size and length into its space.
Give the expansion allowance 1/8 in vertical clearance.
Use new packing.
Close the cap.
After fitting, warm the glass by steam.
Tighten the gland nut.
Then steam and water pressure should be tested whether they are fair and clear.
Close the drain and open the water and steam side cocks.
Check the leakage; all are satisfactory put back into operation.
Routine boiler maintenance carried out on ships ?
Clean the rotating cup.
Check and adjust the belt tension between motor and rotating shaft.
Clear the pilot burner nozzle and fitter.
Clean carbon deposit on electrodes ( igniter ) and adjust the gap.
Check the fuel valve and air register linkages and joints.
Check and clean the flame eye cover glass.
Check and clean inspection peep hole glass cover.
Clean fuel oil fitter.
Check the fuel oil pressure.
When boiler safety valve setting made ?
Every boiler survey.
After safety valve overhaul.
Why ship side blow down valve is open first and close last ?
To prevent pressure build up in blow down line.
In pipe burst, it may be injurious to watch keeper.
What if no test and treatments is done to boiler ?
Reduction in boiler efficiency due to poor heat transfer
Reduction in tensile strength
Reduction in factor of safety
Overheating of metal resulting distortion and eventual failure
Increase in fuel consumption
Excess concentration of NaOH (caustic soda) may cause caustic embrittlement on boiler metal and tend to failure of boiler metal
Corrosion
Scale formation
Foaming, Priming, carry over (due to increase T.D.S level, foaming is present and tend to carried over and priming)
How to control steam pressure in exhaust gas boilers ?
By regulating the amount of gas flowing over the extended surface, i.e. by damper regulation.
By dividing the unit into sections so that each section is controlled by an inlet valve.
By passing steam through an automatic pressure controlled surplus valve to a dump condenser.
By a system designed for a higher pressure than that it is to operate.
What is meant by soot blow ?
Purpose is to remove soot, to prevent EGE fire or soot fire.
To get steam generating efficiency good
To increase heat transfer efficiency
Time – Day time at sea 2 -3 times/day
What is the procedure to soot blow ?
Inform to bridge
Check wind direction, good if transverse direction
Raise boiler pressure
Open drain cock until soot blow pipe drain clear
Open soot blower valve
Increase the air to boiler to more than 50 %
Open steam valve & carried out by turning wheel 20 -30 sec
Then close steam valve, soot blower valve
Open drain valve
Boiler safety valve examination and attention during overhauling ?
Checked its valve and valve seat for wear, cavity corrosion and any fault.
They should be grounded properly but maker’s limit must be maintained such as width of seating, clearance between valve lip and seat.
Valve chest must be cleaned condition and drain line clear.
The spring should be hammer tested for any fracture and check for corrosion. Free length is limited to 0.5 % of original free length.
The spindle should be hammer tested for any crack and its straightness.
The guide plates and bushes are checked for uneven wear and have sufficient clearance to allow free movement of spindle.
The compression nut and cover bush’s threads are carefully checked it for any sign of wear and tear.
The easing gear should be checked in good order including bearings, cable pulley, and connecting links.
Connecting pin should be a free fit in the lid and pin should not bent or pinhole gone out of shape.
All safety valves are to be set to operate under steam a little above working pressure not greater than 3% above the approve working pressure of the boiler.
Why safety valve is fitted in two numbers ?
To make sure that the positive discharging of higher steam pressure from boiler efficiency.
Why fitted in one valve chest ?
To reduce stress by hole on pressure vessel (boiler)
To minimize the numbers of cutting hole on boiler to save it’s strength.
What is meant by erosion in boilers ?
It is a mechanical attack on the metal surface which may be due to a disturbance in the flow of the fluid over the metal surfaces, resulting in a loss of metal. Suspended abrasive matters in the fluid can increase the rate of metal losses.
What is meant by corrosion in boilers ?
It is the deterioration of metals due to oxidation. The present of water in an acidic condition provides the electrolyte required for corrosion action.
Two forms of corrosion
Direct chemical attack
It occurs when metal at high temperature comes into contact with air or other gases, resulting in oxidation or sulphidation of the metal.
Electro-chemical action
Galvanic action, this being set up when two dissimilar metals are placed in an electrolyte. The noble of the two metals form a cathode to the base metal which, forming the anode, is wasted away.
What is meant by caustic embrittlement in boilers?
Caustic embattlement is a form of inter crystalline cracking, which results from a solution of sodium hydroxide or caustic soda, becoming more and more concentrated at the bottom of a crack or fissure (narrow opening) which may be the result of fatigue, in the boiler plate or furnace.
The plate must be stressed, so that wastage take place at the bottom of crack, the plate weakens, the crack extends to expose new metal to the caustic action and thus it proceed.
Caustic embattlement will only occur when there is a high caustic alkalinity that is when the ratio of NaOH to the alkalinity is high. To keep this ratio at the safe level the sodium sulfate to sodium hydroxide should be maintained above 2:5.
The sodium sulfate comes out of solution in high sodium hydroxide concentration and by doing forms a protective layer on the surface of the plate.
Also keep the lowest T.D.S level. (Total dissolved suspended & solid)
What is pH value for boiler water ?
It is the logarithm of reciprocal of hydrogen iron concentration.
What do you do for preventing of oxygen in boilers?
The oxygen-scavenging chemical which is used for deaeration the water are usually sodium sulphate or hydrazine.
2Na2SO3 + O2 = 2Na2SO4
N2H4 + O2 = 2H2O +N2
Excessive dosage of hydrazine could lead to steam and condensate line corrosion due to ammonia being produced as the excess hydrazine decomposed.
In high pressure boiler, by using the sodium sulphite, the sulphite can break down to give hydrogen sulphide which can attack steel brass and copper.
If chloride is found too much in your boiler water what will you do ?
Blow down frequently
Reduce the boiler load to minimum.
If highly contaminant shut down completely and wash out.
Trace and find out the fault and remedies.
What do you understand by composite boiler ?
If exhaust gas and oil fired can be used the same time, it is termed the composite boiler.
In this type a separate tube nest of tube for exhaust gas is provided, situated above the return tubes from the fire furnace.
Uptake from the tube nest are separated.
What do you understand by alternative boiler ?
If the exhaust gas and the oil fire are arranged to be used only at a time, the exhaust gas boiler term as the alternative boiler.
This unit can be oil fire heated by the exhaust gases alternatively.
It required only one uptake.
What do you understand by economizer boiler ?
In this system a separate exhaust gas economizer is connected to an oil fired auxiliary boiler or an accumulator by means of piping and a set of circulation pump.
Exhaust gas is used as heating medium and it has no steam space.
What is meant of accumulation pressure in marine boilers?
Accumulation pressure is the rise in boiler pressure which take place when the spring loaded safety valve lift due to the increase loading caused by further compression of the spring.
What is the purpose of accumulation pressure test ?
To detect the safety valve is suitable for this boiler or not.
To limit the rise in boiler pressure under full fire condition.
What is the procedure of accumulation pressure test ?
This test is carried out a new boiler or new safety valve.
Shut off feed water
Closed main steam stop valve.
Increase cut off pressure of boiler.
Bypass high pressure cut off of the boiler.
Arrange the boiler fire rate to a maximum.
Safety valve will be lift during the test.
The test is carried out as long as the water permits in the boiler.
Accumulation pressure should not exceed 10% of working pressure in the specified time.
Specified time is 15 mins for a smoke tube boiler and 7 mins for water tube boiler.
Procedure of safety valve setting under steam pressure ?
Setting of safety valves:
Take standard pressure gauge (approved by surveyor) for accuracy.
Fill up water up to ¼ of gauge glass level, and shut main steam stop valve, feed check valve.
Without compression rings, hoods and easing gears, reassembled the safety valves with spring compression less than previous setting.
Raise the boiler pressure to desired blow off pressure.
Screw-down spring compression nuts of any lifting valves, until all are quite.
Arrange to have the desired steam pressure
Adjust each valve in turn: Slacken compression nut until the valve lifts. Screw-down compression nut sufficiently enough, so that when the valve spindle is lightly tapped, valve return to its seat and remain seated. Measure gap between compression nut and spring casing. Make a compression ring equal to this gap, and insert under compression nut. Gag the spindle of this safety valve, to prevent opening, while remaining valve is being set.
Remaining valve is again set and insert compression ring.
Remove gag and retest both valve to lift and close together.
Cap, cotter and easing gear to be refitted
Caps and cotter pins padlocked to prevent accidentally altering the setting.
When the surveyor satisfied the setting pressure, easing gear should be tested.
All safety valves set to lift at not greater than 3% above approved working pressure (design pressure).
How do you take action if one of the passages of gauge glass is chocked ?
Steam and water cocks and passages in the gauge can be cleared while the boiler is still steaming.
To do this, shut the steam and water cocks and open the drain cock.
Remove the check plug opposite the obstruction.
Insert the cleaning plug. Screw in the plug with small hole about 5 mm diameter, drilled through it in place of the cleaning plug.
Insert into this hole a rod of such a size that held by a gloved hand, it can be easily moved without being stuck.
Then open the chocked and push the rod through to clear the blockage.
When clear, open drain to prevent a build up of pressure and only a small amount of steam will blow past the rod, the glove protecting the operator from injury.
Then close the cock and replace the normal cleaning plug. The gauge glass can be tested now and if satisfactory return to service.
Do not carry out this operation on a plate type glass on a high pressure boiler.
What are the causes of boiler furnace blow back ?
Insufficient purging time
Accumulation of oil in furnace from the leaky burners
Boiler tubes and uptake have full of soot deposits.
Air registers control not operating for the high flame mode.
Too little air
Insufficient oil temperature
How to keep boiler not in service ?
For fire tube boiler out of service for short period
The boiler must be completely filled with alkaline water.
The boiler must be topped up periodically and any air in the system must be got rid off.
Regularly test the boiler water and keep the alkalinity in the range of recommended value.
If the boiler is to be taken out of service for long period
It should be drained completely and open up.
Dried out by means of heater units.
Then the trays of quick lime (moisture absorbent material) should be place internally in suitable positions.
Blanks should be fitted to the pipe connections in the event of steam being maintained in other boiler and blow down line.
The quick lime should be renewed at least once every two months.
What is the purposes of boiler water treatment ?
To prevent scale formation ( Trisodium phosphates is used)
To remove trace of oxygen (sodium sulphide or hydrazine is used )
To give alkalinity and minimize corrosion.(sodium hydroxide is used )
To reduce risk of caustic cracking ( sodium sulphate or sodium nitrate is used)
What is the difference between safety valve and relief valve ?
Safety valve
Directly open the design lift at set pressure.
Can open manually by easing gear.
Setting pressure is just above the working and not more than 3% above the approved working pressure.
Relief valve
Setting pressure is 10% above working pressure .
Opening is proportion to the increase in pressure.
Can not be open manually.
What are the markings on safety valve ?
Manufacturer’s name
Serial number
Inlet diameter
Operating pressure
Discharge capacity
Safe working pressure
Blow off pressure
Auxiliary boiler uptake or flue gases normally pass through economisers or air pre-heaters or feed water heaters. All these types of heat exchangers are fin type. Hence large amount of carbon or soot deposits on the fins. Along with the flue gases some un-burnt carbon particles also get deposited on the economisers. Normally dry soot deposits have a very high ignition temperature. But when the soot gets wet with hydrocarbon vapours, their ignition temperature comes down to around 150 degree Celsius. This may result in boiler soot fire or boiler uptake fire. When an uptake fire is suspected, never soot blow the economiser. Soot blow with steam causes steam to convert as hydrogen gas and result in metal fire.
Preventive Actions
Regularly inspect boiler flame to ensure correct air fuel ratio is maintained. This makes complete combustion with clean flue gas.
Carry out boiler burner and swirler routines as per PMS.
Regularly soot blow economisers and water wash periodically to remove soot deposits.
Use proper grade of fuel oil for boiler.
Fuel oil used for boiler to be treated well.
Avoid low load operation of boiler for long period.
Running boiler near full load periodically, helps in expelling out carbon deposits adhered in uptake passages and reduces chances of boiler uptake fire considerably.
What is exhaust gas economiser (EGE) fire and how it occur ?
A flame appear at the economizer coil during running of main engine at sea while the EGE is put into service with circulation water passing through the coils, it is called economizer fire.
It is actually cause by soot fire at the economizer coils.
For the economizer coils fire, heat is already presented due to passing the gases of main engine.
Air is available due to excess supply of scavenging air into the unit combustion chamber.
Thick deposit of unburnt fuel, carbon residue (soots) are sticking at the economizer coils .
Soots are formed from incomplete combustion and use of low grade fuel and high carbon content fuel.
At the manoeuvring time, the more incomplete combustion may occur and at that time leaving flue gas velocity is very low, thus unburnt fuel can be adhering on the economizer coils.
A flame is produced when air and fuel are proportionally mixed in the sufficient heating temperature.
What are the indications of EGE fire ?
Smoke smell will get from the economizer.
Over heat at economizer body ( external casing of uptake.)
Heavy smoke and sparks will emit from the funnel.
Sudden unexpected increase in uptake gas temperature ( Abnormally high stack pyrometer reading)
Flame visible in the smoke indicator.
How to prevent EGE fire on ships ?
To get complete combustion of fuel, maintain the main engine (ME) in optimum combustion condition.( governor, fuel injection pump, fuel injection valve, fuel injection timing, fuel condition, air cooler, turbocharger, do not run too long ME with slow speed)
Regular open up & cleaning smoke side of economiser depending upon soot accumulation. (water washing)
Regular soot blowing operation. Check & maintain soot blowing equipment.
Regular overhaul boiler burner, correct air fuel ratio & damper.
What are the actions to be taken during economizer fire ?
Inform to the bridge and chief engineer. Take the permission to stop main engine.
Gradually slowdown the ME and then stop.
If fire fighting equipment is fitted, it should be brought into operation.
Cool down the economizer by means of boundary cooling.
Circulation pump must be run but, if large amount of water lost it must be stopped.
There is no heat source and fire is out.
When economizer fire occurs never do soot blow to economizer.
It can cause hydrogen fire and melt down the coils stack. It can cause deformation and tube bulking because intensive heat and high thermal stress formed at economizer coils.
What are the actions to be taken after economizer fire ?
Cool down to ambient temperature.
Open the economizer cover.
Clean inside parts of the economizer.
Check the any defective coil and repair for temporary used by welding or plugging the tubes.
How to effectively fight the economiser fire ?
Slow down the engine.
Shut off oil burners, draught fans, dampers & air register.
Raise water level full and blow down continuously so as to maintain good flow of water.
Reduce boiler pressure by easing gear.
Spray water on the external casing of the uptake to cool the affected area.
A few times starting and stopping of main engine should be done to blow out collected soots at the uptake.
What is self perpetuating fire or hydrogen fire on ships ?
When the fire causes the metal itself burning at about 700 °C, if steam smothering soot blowing system or water jetting system have been attempted, the big hydrogen fire may result.
The applied steam dissociates into hydrogen and oxygen and accelerating the fire.
Once such a fire has started, resulting two kind of fires may take place simultaneously, one kind, iron burning in steam, and the other, the hydrogen burning in an air exothermic way.
This combined fire being self supporting and lasting until the supply of steam is exhausted.
The primary objective of dealing the fire is to cool the surface and burning material as quickly as possible.
The boiler maintenance should always be executed with skill and in accordance with valid rules and regulations from the authorities, and below are given some recommendations for periodical inspections and maintenance.
Daily Operation
During normal operation of the boiler some work and check procedures have to be considered every day.
Check the boiler steam pressure and the water level.
Check that the feed water control system is operational.
Check the boiler water condition and make necessary countermeasures with regard to the feed and boiler water treatment. If necessary blow-down the boiler.
Check the function of the oil burner at different capacities through the inspection holes on the boiler.
Check the flue gas temperature after and/or the draft loss across the boiler. If either the temperature or the draft loss is too high, the pin-tube section must be cleaned.
Weekly Routine Checks
Drain each water level glass for about 10-15 seconds.
In case of contaminated boiler water or insufficient water treatment, the draining of the water level glasses must be done more often.
Check the safety water level device.
Depending on the boiler water tests blown-down the boiler. Open the blow-down valves quickly for a few seconds, and then close and open again for about 5-10 seconds.
Repeat this operation when required according to the boiler water tests.
Perform scum blow out by means of the scum valve when required. The scum blow out must be carried out until the drained water is clean.
Monthly Routine Checks
Test all stand-by pumps.
Check all boiler mountings for damage or leaks and repair/replace if necessary.
Check the function of the high steam pressure switch by lowering the set point or by raising the steam pressure, e.g. by closing the main steam valve slowly. The burner must stop automatically.
Inspection of Furnace
The furnace should be inspected at least twice a year. During this inspection the following issues should be taken into consideration:
Check for cracks at the refractory lining and that the furnace walls are free from excessive soot deposits.
Examine carefully the area opposite the burner. Too much soot deposits indicate that the burner should be adjusted.
Check that the pin-tube elements are intact and that soot deposits are within normal limits.
Inspection of Boiler Water Side
The boiler water side (interior) must be carefully inspected at least twice a year. This inspection of great importance and no doubt the most important of all the maintenance measures, since it has a direct influence on the boiler longevity and on the security.
At these inspections, hard deposits, corrosion and circulation disturbances can be found at an early stage, and preventive measures must be taken to avoid unexpected material damage and boiler breakdown.
Presence of hard deposits at the furnace wall and the pin-tubes reduces their heat transfer properties and decrease the capacity of the boiler.
Further, it is possible to make out if the feed water treatment has been satisfactory and if the blow-down has been carried out sufficiently.
Incorrect feed water treatment is commonly causing hard deposits or corrosion.
Insufficient blow-down will cause sludge deposits in the tubes and accumulation of sludge in the bottom of the boiler.
If hard deposits are not removed, it may lead to overheating in the boiler plate material which is exposed to the flame in the furnace wall area. This may cause material damages.
Incorrect feed water treatment does not always lead to hard deposits. For example, a too low or too high a pH-value may give an electrolytic reaction, causing corrosion in the boiler.
When the boiler interior is inspected, examine all parts carefully and be attentive to deposits, corrosion and cracks. It is advisable to pay special attention to this inspection.
Procedure and Remarks for Inspection
Shut off the boiler and allow it to cool (below 100°C). The boiler should NOT be depressurised by lifting the safety valves and then filled with cold feed water since the stress induced by too rapid cooling may cause damage.
Empty the boiler and close all valves. If the boiler is connected to a second boiler, check that the valves between them are closed.
Unscrew and remove the manhole hatch(s) on the boiler and enter the boiler when it is sufficiently cold. Check the welding in the boiler. A careful examination should be carried out with respect to any possible corrosion or crack formation.
Special care should be taken to the water line area in the pressure vessel where oxygen pitting may occur.
If deposits are found to be forming in the boiler tubes, the boiler should be chemically cleaned.
It is advisable to consult a company of cleaning specialists who will examine the boiler deposits and treat the boiler accordingly.
After chemical treatment the boiler should be blown-down at least twice a day for approximately one week. This will ensure that excessive sludge deposits due to chemical treatment do not collect in the bottom of pressure vessel.
Contamination
If the boiler is contaminated with foreign substances like oil, chemicals, corrosion products etc., it is very important to act immediately to avoid damages to the boiler.
Layers of thin oil films, mud, etc. exposed to the heating surfaces causes a bad heat transfer in the boiler, leading to overheating followed by burned out pressure parts. In order to remove such contamination, a boiling out or acid cleaning have to be performed immediately.
Corrosion products from the pipe system or insufficient boiler water treatment may result in corrosion in the boiler itself. It is therefore important to observe that such circumstances do not occur in the system.
Corrosion can be broadly classified into two.
Dry Corrosion
Metals have a tendency to return back to their natural state of metal oxides. These metal oxides form a thin layer over them and it prevents further corrosion attack.
Wet Corrosion
Every metals have a specific potential when placed in an electrolyte. When two metals of different potential are placed in an electrolyte, it forms an electro-chemical cell. This results in flow of electrons to and from the metals. Even different parts of a single metal can have different potentials in certain conditions. This also may set up an electro-chemical cell or galvanic cell or corrosion cell.
Whatever be the case a cell means there is an anode and cathode, in which anode loses electrons and deteriorates with time. While at the cathode two conditions are there:
If electrolyte is acidic, hydrogen gas is released.
If electrolyte is alkaline, polarizing layer of hydrogen is formed, which prevents further corrosion.
Another thing to be noted is that when there is dissolved oxygen in the electrolyte, the polarizing layer of hydrogen is reacted with oxygen to form water. So no more protection for the metal.
The variation in rate of corrosion with alkalinity at different dissolved oxygen content is shown below.
nfluence of Alkalinity on Corrosion Rates of Carbon Steel with Varying Dissolved Oxygen Contents
Where,
High Dissolved Oxygen
Medium Dissolved Oxygen
Low Dissolved Oxygen
Nil Dissolved Oxygen
The graph clearly explains the effect of high dissolved oxygen content and alkalinity of boiler water in rate of corrosion.
Procedure
Boiler is a pressurized vessel. Incorrect opening procedure could lead to personnel injury as well as equipment damage.
Change over boiler fuel oil to diesel oil.
Make sure all diesel engines are stopped or changed over to diesel oil.
Electric fuel oil heaters can be put in use if fitted on board.
Shut main steam stop valve and put off feed water pump.
Carry out scum blow down to remove floating oil, sludge, etc.
Carry out bottom blow down after scum blow down, otherwise oil carry over may occur.
Boiler blow down to be carried out in steps to avoid thermal stresses. Excessive stresses may lead to cracking.
Sudden cooling down and drop in pressure may cause stresses in boiler. So reduction of pressure must be gradual.
Make sure nobody is standing near ship side blow down valve.
Gradually reduce boiler pressure in steps, 5bar—–>4.5bar——>4bar and so on. This helps in gradual reduction in boiler temperature also.
Safety gear to be used by the personnel operating blow down valves.
When boiler pressure reaches 1bar, open up the vent.
Now if the ship is loaded and having high draft, it may not be possible to drain boiler water completely. In such case arrangements to be made for transferring remaining boiler water to bilges.
Once the boiler is fully depressurized, slack top manhole door first, make sure no pressure is inside, support the door with chain block, and slowly remove it and secure.
Now open bottom manhole door slowly. This procedure is to be followed.
Now open remaining mud boxes.
Water washing and inspection of boiler can now be carried out after ventilating sufficiently.
Between periodic boiler cleaning the gas surfaces of the boiler tubes should be kept as clean as practicable. To facilitate this, soot blower, steam or air operated, are often fitted. They enable the tube surfaces to be cleaned of loose sooty deposits rapidly without shut down of the boiler.
Figure below shows a typical soot blower arrangement fitted to a Scotch type boiler.
Working
With steam supplied to the soot blower and the steam supply line thoroughly drained. Rotation of the soot blower hand wheel causes the supply tube and nozzle to move towards the combustion chamber. Nozzle and tube are rotated as they move inwards by means of a scroll cut in the nut and a stationary pin ‘A’ in the body assembly that runs in the scroll. Ports in the tube communicate the steam supply line with the nozzle.
The arrangement enables rotating, fine, high pressure jets of steam to be discharged to the tube plate over a considerable area.
When not in use, the retractable nozzle of the soot blower is well within the housing tube and is therefore protected from overheating, which could cause burning and distortion of the nozzle.
Too frequent use of the soot blower should be avoided as this could cause wastage of the tube plate. It is advisable to operate the blower regularly even if the boiler tubes are clean (in this case without steam supply to the blower) to ensure the blower unit is free and in operable order.
Steam traps are special types of valves which prevent the passage of steam but allow condensate through. It works automatically and is used in steam heating lines to drain condensate without passing any steam. The benefit gained with a steam trap, is that steam is contained in the heating line until it condenses, thus giving up all of its latent heat.
Thermodynamic steam trap use pressure energy of the steam to close the valve which consists of a simple metal disc. The sequence of operation is shown in figure below.
In (i), disc A is raised from seat rings C by incoming pressure allowing discharge of air and condensate through outlet B. As the condensate approaches steam temperature it flashes to steam at the trap orifice. This means that the rate of fluid flow radially outwards under the disc is greatly increased. There is thus an increase in velocity and a reduction in static pressure. The disc is therefore drawn towards the seat. Due to this alone the disc will never seat. However, steam can flow round the edge of the disc resulting in a pressure build up in the control chamber D as shown in (ii). When the steam pressure in chamber D acting over the full area of disc (iii) exceeds the incoming condensate / steam pressure acing on the much smaller inlet area, the disc snaps shut over the orifice. This snap action is important. It eliminates any possibility of wire-drawing the seat, while the seating itself is tight, ensuring no leakage. As shown in (iv) the incoming pressure will eventually exceed the control chamber pressure and the disc will be raised, starting the cycle all over again.
The rate of operation of a steam trap depends upon he steam pressure and ambient air temperature. In practice, the trap will usually open after 15 – 25 seconds; the length of time open depends on the amount of condensate to be discharged. If no condensate have been formed, then the trap snaps shut immediately. From the foregoing it will be seen that the trap is never closed for more than 15 – 25 seconds, so condensate is removed virtually as soon as it is formed.
There are different types of remote water level indicators. Their purpose is to bring the water level reading to some convenient position in the engine or boiler room where it can be distinctly seen. These indicators when fitted are normally in addition to the normal statutory requirements for water gauge fittings for boilers.
Remote Water Level Indicator
Figure above is a diagrammatic arrangement of the ‘Igema’ remote water level indicator. The lower portion of the ‘U’ tube contains a red coloured indicating fluid which does not mix with water and has a density greater than that of water.
The equilibrium condition for the gauge is H = h + ρx, where ‘ρ’ is the density of the indicating fluid. ‘H’, ‘h’, and ‘x’ are variables.
If the water level in the boiler falls, ‘h’ will be reduced, ‘x‘ will be increased and ‘H‘ must therefore be increased. The level of the water in the condenser reservoir being maintained by condensing steam.
If the water level in the boiler rises, ‘h‘ will be increased, ‘x‘ will be reduced and ‘H‘ must therefore be reduced. Water will therefore flow over the weir in the condenser reservoir in order to maintain the level constant.
A strip light is fitted behind the gauge which increases the brightness of the red indicating fluid, which enables the operator to observe at a glance from a considerable distance whether the gauge is full or empty.
A modern high pressure, high temperature water tube boiler holds a small quantity of water and produces large quantities of steam. Very careful control of the drum water level is therefore necessary. The reactions of steam and water in the drum are complicated and require a control system based on a number of measured elements.
When a boiler is operating the water level in the gauge glass reads higher than when the boiler is shut down. This is because of the presence of steam bubbles in the water, a situation which is accepted in normal practice. If however there occurs a higher increase in steam demand from the boiler the pressure in the drum will fall. Some of the water present in the drum at the higher pressure will now ‘flash off’ and become steam. These bubbles of steam will cause the drum level to rise. The reduced mass of water in the drum will also results in more steam being produced, which will further raise the water level. This effect is known as ‘swell’. A level control system which is used only level as a measuring element would close the feed control valve, when it should be opening it.
When the boiler load returns to normal the drum pressure will rise and steam bubble formation will reduce, causing a fall in water level. Incoming colder feed water will further reduce steam bubble formation and what is known as ‘shrinkage’ of the drum level will occur.
The problems associated with swell and shrinkage are removed by the use of a second measuring element, ‘steam flow’ . A third element ‘feed water flow’ is added to avoid problems that would occur if the feed water pressure were to vary.
Three Element Boiler Water Level Control
Three Element Boiler Feed Water Control
A three element boiler water level control system is shown in figure above. The measured variables or elements are ‘steam flow’, ‘drum flow’ and ‘feed water flow’. Since in a balanced situation steam flow must equal feed flow, these two signals are compared in a differential relay. The relay output is fed to a two term controller and comparator into which the measured drum level signal is also fed. Any deviation between the desired and actual drum level and any deviation between feed and steam flow will result in controller action to adjust the feed water control valve. The drum level will then be returned to its correct position.
A sudden increase in steam demand would result in a deviation signal from the differential relay and an output signal to open the feed water control valve. The swell effect would therefore not influence the correct operation of the control system. For a reduction in steam demand, an output signal to close the feed water control valve would result, thus avoiding shrinkage effects. Any change in feed water pressure would result in feed water control valve movement to correct the change before the drum level was affected.
Water tube boilers have to a large extent superseded the smoke tube or fire tube boilers for the supply of steam to main and auxiliary machinery. Even donkey (i.e. auxiliary) boilers are frequently found to be water tube and certainly all modern turbine plants use them for main steam supply.
The advantages of water tube boilers are:
High efficiency (generally greater than 85 %) hence reduced fuel consumption.
Flexibility of design – important space consideration.
Capable of high output (i.e. high evaporation rate).
High pressures and temperatures improve turbine plant efficiency.
Flexible in operation to meet fluctuating demands of the plant – superheat control rapidly responsive to changing demands.
Generally all surfaces are circular hence no supporting stays are required.
Steam can be raised rapidly from cold if the occasion demands (3 to 4 hours compared to 24 hours for smoke tube or fire tube boilers) because of the positive circulation.
Consider a fire tube or smoke tube boiler and a water tube boiler with similar evaporation rates the water tube boiler would be compact and relatively light by comparison and its water content would be about 7 tonnes or less compared with the smoke tube or fire tube boiler’s 30 tonnes.
With double casing radiation loss can be cut to 1 % or less.
Good combustion is essential for the efficient running of the boiler. It gives the best possible heat release and minimum amount of deposits on the heating surfaces. Different types of boiler fuel oil atomizers are:
Simple Pressure Jet Atomizer
Figure below shows diagrammatically the principle of the simple pressure jet boiler fuel oil atomizers. Oil fuel at a pressure of not less than 8 bar is supplied to the tangentially arranged ports, wherein it falls in pressure, resulting in the oil swirling around at high velocity inside the chamber. The greater the pressure drop the greater would be the velocity, but generally supply oil pressure would not be greater than 25 bar, high pressures create pumping and sealing problems.
At outlet from the short sharp edged orifice (care must be taken not to damage the orifice during cleaning) a hollow expanding cone of fuel droplets is produced whose initial film thickness reduces as oil supply pressure increases.
The following features of the simple pressure jet boiler fuel oil atomizers should be noted.
Simple, inexpensive and robust.
No moving parts, hence no possibility of seizure.
Large range of droplet size for one pressure.
Turn down ratio is low, about 2.5 to 1. Turndown ratio is the ratio of the burner throughput maximum to minimum. If say the maximum throughput is 2500 kg/hr, then with a turn down ratio of 2.5 to 1 the minimum throughput will be 1000 kg/hr.
Maximum throughput is about 3200 kg/hr
No alteration in air register arrangement for all outputs, this is a consequence of the low turndown ratio of this type of burner.
To vary throughput the pressure must be altered, this results in variation in droplet size, hence atomization and combustion will be affected.
Spill type of pressure jet atomizer
With this type of boiler fuel oil atomizers, throughput is varied by adjusting the amount of spill, i.e. the return flow from the burner.
Constant differential type atomizer
With the differential pressure between delivery and spill kept constant the pressure drop across the tangential ports is kept constant and the rotational velocity of the fuel in the swirl chamber will not alter. This will keep fuel cone angle and atomization constant.
The main disadvantage with these types of boiler fuel oil atomizers is the large quantity of hot oil being returned, it may prove difficult to keep control over oil temperature.
Plunger type of pressure jet atomizer
Figure below shows the principle of operation of this type of burner, as the oil supply pressure is increased the spring loaded plunger moves to uncover extra tangential oil entry holes. The pressure drop and hence the rotational velocity of the oil remains nearly constant.
Rotary or spinning cup jet boiler fuel oil atomizers
Figure below shows the arrangement in principle. It consists of a motor driven fan, metering pump and fuel cup.
The fuel cup which rotates at 70 to 100 rev/second is supplied with oil at low pressure (1.7 to 4.5 bar) from the metering pump which is used to control the throughput. Due to centrifugal force and opposite swirl of air to fuel the oil film leaving the cup is rapidly broken down into relatively even sized droplets.
Main features are:
High output possible, up to 3600 kg/h.
Low oil supply pressure.
At low throughputs atomization due to reduced oil film thickness is improved.
Wide turndown ratio, up to 20:1 possible.
Oil viscosity need only be reduced to 400 seconds Redwood number 1 for satisfactory operation.
Internal corrosion takes place due to poor quality of feed water or inadequate boiler water treatment. Boiler water may contain dissolved air or gases such as oxygen and carbon dioxide.
Oxidation and Pitting Corrosion
Oxygen in water causes oxidation of steel, resulting in oxidation corrosion.
4Fe + 3O2 ——> 2Fe2O3
This is general corrosion, which causes pitting. In order to prevent this:
Use mechanical deaerators to remove dissolved gases from feed water
Use vacuum condenser and keep hot well closed
Use closed circuit system
Dose chemicals such as HYDRAZINE (It reacts with oxygen and releases nitrogen and water)
N2H4 +O2 ———-> N2 + 2H2O
Carbon dioxide dissolved in water forms carbonic acid.
CO2 + H2O ——–> H2CO3
Chlorides in feed water forms hydrochloric acid.
MgCl2 +2H2O ——–> Mg(OH)2 + 2HCl
Fe + 2HCl ———> FeCl2 + H2
In order to counteract the acidic corrosion, alkaline compounds such as sodium hydroxides are added to boiler water.
MgCl2 + 2NaOH ———> Mg(OH)2 + 2NaCl
Corrosion Due to Scale Formation
Scale formations results in heavy pitting corrosion. Phosphate treatment in boiler water reduces this type of corrosion.
CaSO4, MgSO4, CaCO3 are scale forming compounds
In order to control the corrosion, tri sodium phosphate, Na3(PO4)2, is dosed.
3CaSO4 + Na3(PO4)2 ———> Ca3(PO4)2 + 3Na2SO4
By adding boiler coagulant chemicals, these products from non-sticky sludge and are washed away while regular bottom blow down.
Cause of Boiler furnace Blow Back
Main cause of boiler furnace blow back is accumulation of hydrocarbons inside the furnace. Hydrocarbons may exist as vapours or liquid form inside the boiler furnace. Accumulated fuel vapours inside furnace catches fire and develops high pressure inside the furnace thereby resulting in dangerous explosion. It is a usual practice that when there is frequent flame failure, operator try to fire the boiler in manual mode. In manual mode pre purging is not automatically controlled. Hence an attempt is made to fire boiler with insufficient pre purging time and eventuality may be catastrophic explosion.
Preventive Actions
Allow sufficient time for pre purging the furnace with dampers full open to ensure all the accumulated vapours are expelled out.
Purging to be carried out 5-6 times the furnace volume for effective expelling.
Never try to reduce purging time or bypass it.
Carry out boiler burner and swirler routine as per planned maintenance system.
Do not fire boiler with heavy fuel oil or sludge if it is not designed for the same.
Air fuel ratio of oil compound regulator to be adjusted correctly to maintain proper and complete combustion.
Pilot burner to be maintained in good condition so that flame failure while starting does not occur.
Igniter or ignition transformer, its leads, etc. to be properly insulated and tightened.
Fuel oil fed to the boiler to be properly treated as per manufacturer’s recommendations.
If an economizer or pre heater is fitted in the boiler exhaust, same to be water washed and inspected regularly to avoid back pressure of gases.
Conduct furnace inspections periodically to inspect conditions inside.
When a flame failure is experienced find and rectify the root cause. Do not try to fire again and again.
ABMA - American Boiler Manufacturers Association.
ABRASION - The wearing away of a surface by rubbing, as with sandpaper on wood.
ABRASION RESISTANCE - The ability of a material to resist surface wear.
ABRASIVE EROSION - Erosive wear caused by the relative motion of solid particles
which are entrained in a fluid, moving nearly parallel to a solid surface.
ABSOLUTE HUMIDITY - Amount of moisture in the air, indicated in kg/kg of dry air.
ABSOLUTE PRESSURE - Total pressure measured from an absolute vacuum. It equals
the sum of the gauge pressure and the atmospheric pressure corresponding to the
barometer.
ABSOLUTE PRESSURE - Air at standard conditions (70°F air at sea level with a
barometric pressure of 29.92 in Hg) exerts a pressure of 14.696 psi. This is the pressure
in a system when the pressure gauge reads zero. So the absolute pressure of a system is
the gauge pressure in pounds per square inch added to the atmospheric pressure of
14.696 psi (use 14.7 psi in environmental system work) and the symbol is "psia".
ABSOLUTE TEMPERATURE SCALE - A scale of temperature measurement in which zero
degrees is absolute zero.
ABSOLUTE ZERO - A hypothetical temperature at which there is total absence of heat.
Since heat is a result of energy caused by molecular motion, there is no motion of
molecules with respect to each other at absolute zero. It is theoretically the coldest
possible temperature.
ABSOLUTE ZERO TEMPERATURE - Temperature measured from absolute zero (-
459.67°F, or -273.16°C).
ABSORBENT - A material which, due to an affinity for certain substances, extracts one or
more such substances from a liquid or gaseous medium with which it contacts and which
changes physically or chemically, or both, during the process. Calcium chloride is an
example of a solid absorbent, while solutions of lithium chloride, lithium bromide, and
ethylene glycols are liquid absorbents.
ABSORBER - That part of the low side of an absorption system, used for absorbing vapor
refrigerant.
ABSORPTION - A process whereby a material extracts one or more substances present in
an atmosphere or mixture of gases or liquids accompanied by the material's physical
and/or chemical changes.
ABSORPTION REFRIGERATION SYSTEM - One in which the refrigerant, as it is
absorbed in another liquid, maintains the pressure difference needed for successful
operation of the system.
ABSORPTION REFRIGERATOR - Refrigerator that creates low temperatures by using the
cooling effect formed when a refrigerant is absorbed by chemical substance.
ABSORPTION SYSTEM - A refrigeration system in which the refrigerant gas evolved in
the evaporator is taken up in an absorber and released in a generator upon the application
of heat.https://boilersinfo.com
ABSORPTION TOWER - A tower or column, which effects contact between a rising gas
and a falling liquid, so that part of the gas may be taken up by the liquid.
ACCELERATION - The rate of change of velocity, as a function of time. Expressed in m/s.
ACCELERATION DUE TO GRAVITY - The rate of increase in velocity of a body falling
freely in a vacuum. Its value varies with latitude and elevation. The International Standard
is 32.174 ft. per second per second.
ACCELERATION PERIOD - In cavitation and liquid impingement erosion, the stage
following the incubation period, during which the erosion rate increases from near zero to
a maximum value.
ACCELRATION - The time rate of change of velocity; i.e., the derivative of velocity; with
respect to time.
ACCEPTABLE WELD - A weld that meets all of the requirements and the acceptance
criteria prescribed by the welding specifications.
ACCESSIBLE HERMETIC - An assembly of motor and compressor, inside a single bolted
housing unit.
ACCUMULATOR - Storage tank which receives liquid refrigerant from evaporator and
prevents it from flowing into suction line before vaporizing.
ACETONE - A filler added to acetylene cylinders, capable of absorbing 25 times its own
volume of acetylene.
ACID - Literally hitter, but chemically the state of a water solution containing a high
concentration of hydrogen ions.
ACID ATTACK - Caused by an incomplete flushing after an acid cleaning process of
boilers or similar equipment.
ACID CLEANING - The process of cleaning the interior surfaces of steam generating units
by filling the unit with dilute acid accompanied by an inhibitor to prevent corrosion and by
subsequently draining, washing, and neutralizing the acid by a further wash of alkaline
water.
ACID CONDITION IN SYSTEM - Condition in which refrigerant or oil in a system, is
mixed with vapor and fluids that are acidic in nature.
ACID EMBRITTLEMENT - A form of hydrogen embrittlement that may be induced in
some metals by an acid.
ACID GAS - A gas that that forms an acid when mixed with water. In petroleum
processing, the most common acid gases are hydrogen sulfide and carbon dioxide.
ACID RAIN - Atmospheric precipitation with an pH below 5.6 to 5.7.
ACID SOAK - A method of acid cleaning, in which the acid is pumped into the boiler and
rests there for a period of time.
ACIDIC - The reaction of a substance with water resulting in an increase in concentration
of hydrogen ions in solution (see acid).https://boilersinfo.com
ACIDIFIED - The addition of an acid (usually nitric or sulfuric) to a sample to lower the
pH below 2.0. The purpose of the acidification is to "fix" a sample so it will not change
until it is analyzed.
ACIDITY - Represents the amount of free carbon dioxide, mineral acids, and salts
(especially sulfates of iron and aluminum) which hydrolyze to give hydrogen ions in the
water. The acidity is reported as millie equivalents per liter of acid, or ppm acidity as
calcium carbonate, or pH, the measure of hydrogen ion concentration.
ACOUSTIC - A term pertaining to sound, or the science of sound.
ACROSS THE LINE - A method of motor starting, which connects the motor directly to
the supply line on starting or running.
ACTION - Refers to the action of a controller. It defines what is done to regulate the final
control element to effect control.
ACTIVATED ALUMINA - Chemical which is a form of aluminum oxide. It is used as a
drier or desiccant.
ACTIVATED CARBON - Is a specially processed carbon, used as a filter drier. Commonly
used to clean air.
ACTIVATED SLUDGE - An aerobic biological process for conversion of soluble organic
matter to solid biomass, removable by gravity or filtration.
ACTIVE STORAGE PILE - A method of stockpiling coal, sometimes called live storage.
The pile is located outside the plant but adjacent to it, and usually contains four or five
days of operating supply. The pile is not compacted, as it is not stored long enough to be
exposed to the hazard of spontaneous combustion.
ACTUATOR - The portion of a regulating valve, which converts mechanical, fluid, thermal,
or electrical energy; into mechanical motion to open or close the valve seats or other such
devices.
ADIABATIC - Occurring with no addition or loss of heat from the system under
consideration.
ADIABATIC CHANGE - A change in the volume, pressure, or temperature of a gas,
occurring without a gain of heat or loss of heat.
ADIABATIC COMPRESSION - Compressing a gas without removing or adding heat.
ADIABATIC COOLING - A method in which paramagnetic salts are pre-cooled, and then
demagnetized, thereby producing further cooling.
ADIABATIC EFFICIENCY -The ratio of actual work output of a heat engine to the ideal
output.
ADIABATIC EXPANSION - The expansion of a gas, vapor, or liquid stream from a higher
pressure to a lower pressure, with no change in enthalpy.
ADIABATIC PROCESS - A thermo-dynamic process in which no heat is extracted from or
added to the system of the process.
ADIABATIC SATURATION PROCESS - A process to determine absolute or relative
humidity
ADJUSTABLE DIFFERENTIAL - A means of changing the difference between the control cut
in and cutout points.
ADJUSTABLE RESISTOR - A resistor whose value can be mechanically changed, usually by
the use of a sliding contact.
ADSORBENT - A material which has the ability to cause molecules of gases, liquids or
solids to adhere to its internal surfaces without changing the adsorbent physically or
chemically. In water treatment, a synthetic resin possessing the ability to attract and to
hold charged particles.
ADSORPTION - The adhesion of the molecules of gases, dissolved substances, or liquids in
more or less concentrated form, to the surface of solids or liquids with which they are in
contact. Commercial adsorbent materials have enormous internal surfaces.
ADSORPTION INHIBITORS - They are materials which caused them to be adsorbed on to
the metal surface due to their polar properties.
ADVECTION - The transfer of heat by horizontal movement of air.
AERATION - Exposing to the action of air, like blowing air through water before
discharging to a river.
AERATION CELL - (see oxygen cell)
AEROBIC - A condition in which "free" or dissolved oxygen is present in water.
AERODYNAMIC NOISE - Also called generated noise, self-generated noise; is noise of
aerodynamic origin in a moving fluid arising from flow instabilities. In duct systems,
aerodynamic noise is caused by airflow through elbows, dampers, branch wyes, pressure
reduction devices, silencers and other duct components.
AGGLOMERATE - The clustering together of a few or many particles into a larger solid
mass.
AGITATOR - A device used to cause motion in confined fluids.
AIR - A substance containing by volume approximately 78 - 79% nitrogen; 20.95%
oxygen, .94% argon, traces of carbon dioxide, helium, etc.
AIR BLAST TRANSFORMER - A transformer cooled by forcing a circulation of air around its
windings.
AIR CAPACITOR - Is a capacitor, which uses air as the dielectric between the plates.
AIR CHANGES - A method of expressing the amount of air leakage into or out of a building
or room in terms of the number of building volumes or room volumes exchanged.
AIR CLEANER - A devise used to remove air borne impurities.
AIR COIL - Coil on some types of heat pumps used either as an evaporator or a
condenser.
AIR CONDITIONER - They are basically refrigeration devices cooling air and rooms rather
then food compartments. https://boilersinfo.com
AIR CONDITIONER, UNITARY - An evaporator, compressor, and condenser combination;
designed in one or more assemblies, the separate parts designed to be assembled
together.
AIR CONDITIONING -The process of treating air to simultaneously control its temperature,
humidity, cleanliness, and distribution to meet the requirements of the conditioned space.
AIR CONDITIONING UNIT - An assembly of equipment for the treatment of air so as to
control, simultaneously, its temperature, humidity, cleanliness and distribution to meet the
requirements of a conditioned space.
AIR CONDITIONING, COMFORT - The process of treating air so as to control
simultaneously its temperature, humidity, cleanliness and distribution to meet the comfort
requirements of the occupants of the conditioned space.
AIR COOLER - A factory-encased assembly of elements whereby the temperature of air
passing through the device is reduced.
AIR DIFFUSER - A circular, square, or rectangular air distribution outlet, generally located
in the ceiling and comprised of deflecting members discharging supply air in various
directions and planes, and arranged to promote mixing of primary air with secondary room
air.
AIR DIFFUSION AERATORS - They are aerators into which air is pumped into the water
through perforated pipes, plates, or any other method.
AIR DUCT - A tube or conduit for conveying air from one place to another.
AIR FLOTATION - A process of accelerating sedimentation, by introducing air into the
water, this lowers the density of the water, and increases the differences in the densities
of the water and the suspended particles. (DAF), Dissolved Air Flotation.
AIR GAP -The space between magnetic poles, or between the rotating and stationary
assemblies in a motor or generator.
AIR HANDLER - The fan blower, heat transfer coil, filter, and housing parts, of a system.
AIR INFILTRATION – The leakage of air into a room through cracks in doors, windows, and
other openings.
AIR PURGE - The removal of undesired matter by replacement with air.
AIR SATURATED - Moist air in which the partial pressure of the water vapor is equal to the
vapor pressure of water at the existing temperature. This occurs when dry air and
saturated water vapor coexist at the same dry-bulb temperature.
AIR SENSING THERMOSTAT - A thermostat unit, in which the sensing element is located in
the refrigerated space.
AIR STANDARD - Air having a temperature of (20°C), a relative humidity of 36 percent,
and under a pressure of 14.70 PSIA. The gas industry usually considers (16°C) as the
temperature of standard air.
AIR VENT - Valve, either manual or automatic, to remove air from the highest point of a
coil or piping assembly.https://boilersinfo.com
AIR WASHER - A water spray system or device for cleaning, humidifying, or dehumidifying
the air.
AIR, AMBIENT - Generally the air surrounding the object.
AIR, DRY - Air without contained water vapor.
AIR, OUTDOOR - Air taken from outdoors and, therefore, not previously circulated through
the system.
AIR, RECIRCULATED - Return air passed through the conditioner before being again
supplied to the conditioned space.
AIR, REHEATING - In an air conditioning system, the final step in treatment, in the event
the temperature is too low.
AIR, RETURN - Air returned from conditioned or refrigerated space.
AIRBORNE SOUND - Sound which reaches the point of interest by radiation through the
air.
AIR-COOLED CONDENSER - Heat of compression is transferred from condensing coils to
surrounding air. This may be done either by convection or by a fan or blower.
AIR-SENSING THERMOSTAT – A thermostat unit, in which the sensing element is located
in the refrigerated space.
ALCOHOL BRINE - A water and alcohol solution, which remains as a liquid below 0°C.
ALGAE - A minute fresh water plant growth which forms a scum on the surfaces of
recirculated water apparatus, interfering with fluid flow and heat transfer. Lower form of
plant life, usually green and blue green algae appear in cooling water systems. They are
responsible for copious amounts of stringy green slime masses.
ALIVE - A term referring to a circuit in which a current is flowing. Also referred to as live.
ALKALI - A substance having marked basic properties. Applying to hydroxides of
potassium, sodium, lithium, and ammonium. They turn red litmus to blue. Includes
hydroxides of the alkaline earth metals of barium, strontium, and calcium.
ALKALINE - Having a pH greater than 7.
ALKALINE BOIL-OUT - Employed to remove oil and grease deposits from heating surfaces.
ALKALINITY - An expression of the total basic anions (hydroxyl groups) present in a
solution. It also represents, particularly in water analysis, the bi-carbonate, carbonate, and
occasionally, the borate, silicate, and phosphate salts which will react with water to
produce the hydroxyl groups.
ALLEN TYPE SCREW - A screw with a recessed hex shaped head.
ALLOY - A substance having metal properties and being composed of two or more
chemical elements of which at least one is a metal.
ALLOY STEEL - Steel containing specific quantities of alloying elements (other than
carbon)and commonly accepted amounts of manganese, copper, silicon, sulfur, and
phosphorus).https://boilersinfo.com
ALTERNATING CURRENT (AC) - Electric current in which the direction of the current
alternates or reverses. In a 60 Hertz (cycle) current, the direction of current flow reverses
in 1/120th of a second; most commonly used current.
ALTERNATOR - A device which converts mechanical energy, into alternating current.
ALTIMETER - An instrument used to measure the height above a reference point, such as
ground or sea level.
ALUM - Is an aluminum sulfate or filter alum. Acts in the range of 5.0 to 8.0 pH.
ALUMINA - Aluminum oxide occasionally found as an impurity in water in very small
amounts.
AMBIENT AIR TEMPERATURE - Temperature of fluid (usually air) which surrounds object
on all sides.
AMBIENT CONDITIONS - The conditions of temperature, pressure, and humidity, existing
around an instrument.
AMBIENT NOISE -The normal sound in a room or other location.
AMERICAN STANDARD PIPE THREAD - A type of screw or thread, commonly used on pipe
fittings to assure a tight seal.
AMERICAN WIRE GAUGE (AWG) - A system used in the United States for measuring the
size of solid wires.
AMINE - A chemical use in water treatment as a filming or neutralizing agent to protect
the metal parts.
AMMETER - An instrument for measuring the magnitude of electric current flow.
AMMETER SHUNT - A low-resistance conductor, placed in parallel (shunt) with an ammeter
movement, so that most of the current flows through the shunt, and only a small portion
flows through the ammeter. This extends the useful range of the meter.
AMMONIA - Chemical combination of nitrogen and hydrogen (NH3). Ammonia is a very
efficient refrigerant and identified as R-117.
AMORPHOUS - A solid not having a repetitive three-dimensional pattern of atoms.
AMPACITY - A wire's ability to carry current safely, without undue heating. The term
formerly used to describe this characteristic was current capacity of the wire.
AMPERAGE - An electron or current flow of one coulomb per second, past a given point in
a circuit.
AMPERE - The unit used for measuring the quantity of an electrical current flow. One
ampere represent a flow of one coulomb per second.
AMPERE HOUR - A term used for rating battery capacity. As stated, an ampere for an
hour; ex: 5 amperes for 20 hours = 100 amp hour on a 20 hr rating.
AMPERE TURNS - A term used to measure magnetic force. It represents the product of
amperes, times the number of turns of the coil, in an electromagnet.https://boilersinfo.com
AMPLIFICATION - The process of obtaining an output signal greater than the input signal,
through auxiliary power controlled by the input signal. The process of increasing the
strength, current, power, or voltage, of the signal.
AMPLITUDE - The maximum instantaneous value of alternating current or voltage. It can
be in either a positive or negative direction. The greatest distance through which an
oscillating body moves from the mid point.
ANAEROBIC - A condition in which "free" or dissolved oxygen is not present in the water.
ANALYSIS - The process of determining the composition of a substance, by chemical or
physical methods.
ANEMOMETER - An instrument for measuring the velocity of a fluid.
ANGLE OF LAG OR LEAD - The phase angle difference, between two sinusoidal wave forms
having the same frequency.
ANGLE VALVE - A type of globe valve design, having pipe openings at right angles to each
other. Usually one opening on the horizontal plane and one on the vertical plane.
ANGSTROM UNITS - A unit of wave length, equal in length to one ten billionth.
ANHYDROUS CALCIUM SULFATE - A dry chemical, made of calcium, sulfur, and oxygen.
ANION - A negatively charged ion such as the chloride ion (Cl- ).
ANION INTERCHANGE - The displacement of one negatively charged particle by another on
an anion-exchange material. This principle is used with water treatment.
ANNEAL - To soften by heating and allowing to cool slowly.
ANNEALING - A process of heat treating metal, to get the desired properties of softness
and ductility, (easy to form).
ANODE - In electrolysis or electrochemical corrosion, a site where metal goes into solution
as a cation leaving behind an equivalent of electrons to be transferred to the opposite
electron, called the cathode.
ANODIZING - The treatment of a metal surface whereby the metal is made anodic.
ANSI - American National Standard Institute, which is an organization defining standards
for computer language.
ANSI-B.31.1 - Power Piping.
ANSI-B.31.5 - Refrigeration Piping.
ANTI KNOCK VALUE - A premature explosive combustion, as the detonation of the fuel air
mixture in an internal combustion engine, produces a characteristic knock. The Anti Knock
Value is the measure of its resistance to the condition which tends to produce this knock.
ANTICIPATING CONTROL - One which, by artificial means, is activated sooner than it
would be without such means, to produce a smaller differential of the controlled property.
Heat and cool anticipators are commonly used in thermostats. https://boilersinfo.com
ANTICIPATORS - A small heater element in two-position temperature controllers which
deliberately cause false indications of temperature in the controller in an at tempt to
minimize the override of the differential and smooth out the temperature variation in the
controlled space.
ANTI-CORROSIVE ADDITIVE - A lubricant additive to reduce corrosion.
ANTI-FOAM ADDITIVE (FOAM INHIBITOR) An additive used to reduce or prevent foaming.
ANTIFOAM AGENTS - The reduction of carry over by the addition of polymerized esters,
alcohol’s, and amides. The antifoam agent is absorbed on the steam generating surface
resulting in a hydrophobic condition, causing fewer but larger steam bubbles, which readily
coalesce. These agents also weaken the wall of the bubble formed, causing them to
quickly burst on the water surface.
ANTIFOULANTS - Are materials which prevent fouling from depositing on heat transfer
equipment. Materials that prevent deposits forming; include anti- oxidants, metal
coordinators, and corrosion inhibitors. Compounds that prevent deposition are surfactants.
They act as detergents or dispersants.
ANTIFREEZE - Compounds of glycol’s or alcohol’s, that lower the freezing point of cooling
water systems.
ANTIOXIDANT - A substance which when added in small amounts to petroleum products,
will delay or inhibit undesirable changes; such as the formation of gum, sludge, and
acidity, which are brought about by oxidation.
ANTI-OXIDANT - An additive for the purpose of reducing the rate of oxidation and
subsequent deterioration of the material.
ANTI-SCUFFING LUBRICANT - A lubricant that is formulated to avoid scuffing.
ANTI-SEIZURE PROPERTY - The ability of the bearing material to resist seizure during
momentary lubrication failure.
ANTI-WEAR ADDITIVE - A lubricant additive to reduce wear.
API - American Petroleum Institute.
API GRAVITY (API DEGREE) - A measure of density used in the US petroleum industry.
APPARENT (EMF) - The apparent voltage, as measured by the drop in pressure due to a
current flowing through a resistance.
APPARENT WATTS - The product of volts times amperes, in an alternating current circuit.
AQUEOUS - Watery. A substance containing water.
AQUIFER - A porous, subsurface geological structure carrying or holding water.
ARC - A flash, caused by an electric current ionizing a gas or vapor.
ARC BRAZING - A brazing process in which the heat required is obtained from an electric
arc.
ARC FURNACE - An electric furnace, in which heat is produced by an arc between two
electrodes.https://boilersinfo.com
ARC WELDING - A group of welding processes which produce coalescence of metals by
heating them with an arc, with or without the application of pressure, and with or without
the use of a filler metal.
ARC WELDING - A process where coalescence is obtained by heating with an electric arc.
ARCHIMIDES PRINCIPAL - States that an upward force acting on a body wholly or partly
submerged in a fluid, is equal to the weight of the fluid displaced, and acts through the
center of gravity of the fluid displaced, or the center of buoyancy.
ARMATURE - the rotating part of an electric motor or generator. The moving part of a
relay or vibrator.
ARMATURE AIR GAP - The air space between the stationary and rotating parts of a motor
or generator, through which magnetic lines of force pass.
ARMATURE BACK AMPERE TURNS - The magnetic field produced by current flowing in the
armature winding, that opposes and reduces the number of magnetic lines of force,
produced by the field magnets of a motor or generator.
ARMATURE BAR - Copper bars used in place of wire windings, in large armatures,
generators, or motors.
ARMATURE CIRCUIT - The path that the current takes, in flowing through the windings
from one brush to another.
ARMATURE COIL - The loop or coil of copper wire, placed on the armature core, and
forming part of the winding.
ARMATURE CORE -The laminated iron part of the armature, formed from thin sheets or
disks of steel, on which the windings are placed.
ARMATURE CURRENT - The current flowing from the armature of a generator, to the
armature of a motor. Not including the current taken by the shunt field.
ARMATURE DEMAGNETIZATION - The reduction in the effective magnetic lines of force,
produced by the armature current.
ARMATURE REACTION - The effect, that the magnetic field produced by the current flowing
in the armature, has on the magnetic field produced by the field coils.
ARMATURE REGULATING RESISTORS - Are resistors, designed to regulate the speed or
torque of a loaded motor, by placing a resistance in the armature or power circuit.
ARMATURE RESISTANCE - The resistance of the wire used in the windings of the armature,
measured between the rings or brushes, or from positive to negative terminals.
ARMATURE SLOT -The groove or slot in the armature core, into which the coils or windings
are placed.
ARMATURE TESTER - Any device used for locating faults or defects in the armature
winding.
ARMATURE VARNISH - Is a liquid put on the field and armature windings, to improve the
insulation of the cotton covering on the wires.https://boilersinfo.com
ARMATURE WINDING - All of the copper wire placed on the armature, and through which
the current flows.
AROMATICS - A group of hydrocarbons of which benzene is the parent. They are called
"aromatics" because many of their derivatives have sweet or aromatic odorous.
ARTIFICIAL MAGNET - Is a manufactured magnet, which is distinguished from a natural
occurring magnet.
ASHRAE - The American Society of Heating, Refrigeration, and Air Conditioning Engineers.
ASME - American Society of Mechanical Engineers.
ASME APPENDIX SECTION I - Explains matter which is mandatory, unless specifically
referred to in the rules of the code, including formulas.
ASME BOILER CODE - The boiler code listing standards, specified by the American Society
of Mechanical Engineers, for the construction of boilers.
ASME PART PEB SECTION I - Requirements for electric boilers.
ASME PART PFH SECTION I - Requirements for feedwater heaters.
ASME PART PFT SECTION I - Requirements for firetube boilers.
ASME PART PG SECTION I - General requirements for all methods of construction.
ASME PART PMB SECTION I - Requirements for miniature boilers.
ASME PART PVG SECTION I - Requirements for organic fluid vaporizer generators.
ASME PART PW SECTION I - Requirements for boilers fabricated by welding.
ASME PART PWT SECTION I - Requirements for watertube boilers.
ASME SECTION I - Power Boilers.
ASME SECTION II - Material specifications.
ASME SECTION III - Nuclear Power Plant Components.
ASME SECTION IV - Heating boilers.ASME SECTION IX ASME SECTION V - Nondestructive
examination.
ASME SECTION VI - Recommended rules for the care and operation of heating boilers.
ASME SECTION VII - Recommended rules for the care and operation of power boilers.
ASME SECTION VII APPENDIX - Consists of conversion factors for converting Imperial
units to SI Units.
ASME SECTION VII SUBSECTION C1 - Rules for routine operation of power boilers.
ASME SECTION VII SUBSECTION C2 - Operating and maintaining boiler appliances.
ASME SECTION VII SUBSECTION C3 - Rules for inspection.https://boilersinfo.com
ASME SECTION VII SUBSECTION C4 - Prevention of direct causes of boiler failure.
ASME SECTION VII SUBSECTION C5 - Is partial rules for the design of installations.
ASME SECTION VII SUBSECTION C6 - Operation of boiler auxiliaries.
ASME SECTION VII SUBSECTION C7 - Control of internal chemical conditions.
ASME SECTION VIII - Pressure vessels.
ASME SECTION X - Fiberglass reinforced plastic pressure vessels.
ASME SECTION XI - Rules for inservice inspection of Nuclear Power Plant components.
ASPECT RATIO - The ratio of the length to the width, of a rectangular air grille or duct.
ASPIRATING PSYCHROMETER - A device which draws sample of air through it to measure
humidity.
ASPIRATION - Production of movement in a fluid by suction created by fluid velocity.
ASTM - American Society for Testing and Materials.
ASYNCHRONOUS - Not having the same frequency. Out of step, or phase.
ASYNCHRONOUS GENERATOR - An induction generator.
ASYNCHRONOUS MOTOR - An induction motor, whose speed is not synchronous with the
frequency of the supply line.
ATMOSPHERE - Is the mixture of gases and water vapor surrounding the earth.
ATMOSPHERIC ELECTRICITY - Is static electricity, produced between cloud fronts in the
atmosphere.
ATMOSPHERIC PRESSURE - Pressure exerted by the weight of the atmosphere; standard
atmospheric pressure is 101.325 kPa or 1.01325 bars or 14.696 psia or 29.921 inches of
mercury at sea level.
ATOM - The smallest complete particle of an element, which can be obtained, yet which
retains all physical and chemical properties of the element.
ATOMIC NUMBER - The number of protons found in the nucleus of an atom, of an element.
ATOMIC WEIGHT - The weight of an elementary atom, in relation to the weight of an atom
of hydrogen. A hydrogen atom being taken as 1.00g.
ATOMIZE - Process of changing a liquid to minute particles or a fine spray.
ATTEMPERATING WATER IMPURITY - Refers to turbine deposits caused by impurities in the
water used for attemperators. (Chemicals used with attemperating water should be of the
volatile type).
ATTEMPERATOR - An apparatus for reducing and controlling the temperature of a
superheater vapor or a fluid.https://boilersinfo.com
ATTENUATION - The sound reduction process in which sound energy is absorbed or
diminished in intensity as the result of energy conversion from sound to motion or heat.
ATTRITION - The rubbing of one particle against another in a resin bed; frictional wear
that will affect the site of resin particles.
AUTOMATIC - Self-acting. Operating by its own mechanism, when activated by some
triggering signal.
AUTOMATIC CONTROL - The process of using the differences, between the actual value,
and desired value, of any variable, to take corrective action, without human intervention.
AUTOMATIC CONTROLLER - A device that measures the value of a measured variable, and
operates to correct or limit the deviation from a selected reference. Both measuring and
control applications.
AUTOMATIC DEFROST - System of removing ice and frost from evaporators automatically.
AUTOMATIC EXPANSION VALVE (AEV) - A type of metering device that senses low-side
pressure and modulates in order to maintain low-side pressure constant.
AUTOMATIC EXTRACTION UNIT TURBINE - Bleeds off part of the main steam flow at one,
two, or three points. Valved partitions between selected stages control the extracted
steam pressure at the desired level. When extracted steam flowing through the unit does
not produce enough shaft power to meet the demand, more steam flows through the
turbine to exhaust. Located between steam supply and process steam headers.
AUTOMATIC FROST CONTROL - Control which automatically cycles refrigerating system to
remove frost formation on evaporator.
AUTOMATIC GOVERNING SYSTEM - A system which correlates steam flow, pressure, shaft
speed, and shaft output, for any one turbine unit.
AUTOMATIC ICE CUBE MAKER - Refrigerating mechanism designed to automatically
produce ice cubes in quantity.
AUTOMATIC RESET (INTEGRATION) - Is a type of control, in which the controller output,
changes at a rate proportional to the deviation or error. The output will continue to change
as long as any deviation or error exists.
AUTOMATIC STARTER -
AUTOMATION - The employment of devices, which automatically control one or more
functions.
AUTOTRANSFORMER - A transformer in which both primary and secondary coils, have
turns in common. The step up or step down of voltage, is accomplished by taps in
common windings.
AUXILIARY CONTACTS - A set of contacts that perform a secondary function, usually in
relation to the operation of a set of primary contacts.
AVAGADRO'S HYPOTHESIS - States that equal volumes of different gases, at the same
temperature and pressure, will contain equal numbers of molecules.
AVAGADRO'S NUMBER (N) - The number of elementary units such as atoms, formula
units, molecules, or ions, that constitute one mole of the said particle.https://boilersinfo.com
AVERAGING ELEMENT - A thermostat sensing element which will respond to the average
duct temperature.
AXIAL FAN - Consists of a propeller or disc type of wheel within a cylinder that discharges
air parallel to the axis of the wheel.
AXIAL FLOW COMPRESSOR - Uses rotor blades shaped like airfoils, to bite into the air,
speed it up, and push it into the subsequent stationary blade passages. These passages
are shaped to form diffusers, that slow up the incoming air, and make it pressurize itself
by catching up with the air ahead of it.
AZEOTROPE - Having constant maximum and minimum boiling points.
AZEOTROPIC MIXTURE - Example of azeotropic mixture - refrigerant R-502 is mixture
consisting of 48.8 percent refrigerant R-22 and 51.2% R-115. The refrigerants do not
combine chemically, yet azeotropic mixture provides refrigerant characteristics desired.
ABBIT METAL (see bearing, Babbitt).
BACK PRESSURE - Pressure in low side of refrigerating system; also called suction
pressure or low-side pressure.
BACK PRESSURE TURBINE -
BACK SEATING - Fluid opening/closing such as a gauge opening or to seal the joint where
the valve stem goes through the valve body.
BACK WORK RATIO - Is the fraction of the gas turbine work used to drive the compressor.
BACKGROUND NOISE - Sound other than the wanted signal. In room acoustics, the
irreducible noise level measured in the absence of any building occupants.
BACKING RING - Backing in a form of a ring, generally used in welding of piping.
BACKWASH - The counter-current flow of water through a resin bed (that is, in at the
bottom of the exchange unit, out at the top) to clean and regenerate the bed after
exhaustion (water treatment). Also, the process whereby a filtering mechanism is cleaned
by reversing the flow through the filter.
BACTERIA - Microscopic unicellular living organisms.
BAFFLE - Plate or vane used to direct or control movement of fluid or air within confined
area.
BAGHOUSE - A chamber containing bags for filtering solids out of gases.
BALLAST GAS - Are the nonflammable portion of the gas, such as carbon dioxide.
BAROMETER - Instrument for measuring atmospheric pressure. It may be calibrated in
pounds per square inch, in inches of mercury in a column in millimeters or kPa.
BASE - An alkaline substance.
BASE METAL - The metal present in the largest proportion in an alloy. (Copper is the base
metal in brass)
BASE METAL - The substrate metal that is coated or protected by a surface coating.https://boilersinfo.com
BASICITY - The ability of a substance to boost the pH after neutralizing all the acid
species.
BATCH OPERATION - The utilization of ion-exchange resins to treat a solution in a
container wherein the removal of ions is accomplished by agitation of the solution and
subsequent decanting of the treated liquid.
BAUDELOT COOLER - Heat exchanger in which water flows by gravity over the outside of
the tubes or plates.
BEARING, AIR - A bearing using air as a lubricant.
BEARING, ALIGNING - A bearing with an external spherical seat surface that provides a
compensation for shaft or housing deflection or misalignment.
BEARING, ANNULAR - Usually a rolling bearing of short cylindrical form supporting a shaft
carrying a radial load.
BEARING, ANTI-FRICTION - A bearing containing a solid lubricant.
BEARING, AXIAL LOAD (see bearing, thrust)
BEARING, BABBIT - A bearing metal of non-ferrous material, containing several tin-based
alloys, mainly copper, antimony, tin and lead.
BEARING, BALL - A rolling element bearing in which the rolling elements are spherical.
BEARING, BIG END - A bearing at the larger (crankshaft) end of a connecting rod in an
engine.
BEARING, BIMETAL - A bearing consisting of two layers.
BEARING, BOTTOM END - (see bearing, big end)
BEARING, BUSH - A plain bearing in which the lining is closely fitted into the housing in
the form of a bush, usually surfaced with a bearing alloy.
BEARING, CIRCULAR STEP - A flat circular hydrostatic bearing with a central circular
recess.
BEARING, FIXED PAD - An axial or radial load bearing equipped with fixed pads, the
surface of which a are contoured to promote hydrodynamic lubrication.
BEARING, FLOATING - A bearing designed or mounted to permit axial displacement
between shaft and housing.
BEARING, FLOATING RING - A type of journal bearing that includes a thin ring between
the journal and the bearing. The ring floats and rotates at a fraction of the journal
rotational speed.
BEARING, FLUID - (see hydrostatic bearing)
BEARING, FULL JOURNAL - A journal bearing that surrounds the journal by a full 360°.
BEARING, GAS - A journal or thrust bearing lubricated with gas.
BEARING, HALF JOURNAL - A bearing extending 180° around a journal.https://boilersinfo.com
BEARING, JOURNAL - A machine part in which a rotating shaft revolves or slides.
BEARING, KINGSBURRY TRUST -
BEARING, MAGNETIC - A type of bearing in which the force that separates the relatively
moving surfaces is produced be a magnetic field.
BEARING, MAIN - A bearing supporting the main power-transmitting shaft.
BEARING, MITCHELL -(see tilting pad bearing).
BEARING, NEEDLE - A bearing in which the relatively moving parts are separated by long
thin rollers that have a length-to-diameter ratio exceeding 5.0.
BEARING, NONCONTACT - A bearing in which no solid contact occurs between relatively
moving surfaces.
BEARING, PEDESTAL - A bearing that is supported on a column or pedestal rather than on
the main body of the machine.
BEARING, PIVOT - An axial load bearing, radial-load-type bearing which supports the end
of a shaft or pivot.
BEARING, POROUS - Made from porous material, such as compressed metal powders, the
pores acting either as reservoirs for holding or passages for supplied lubricant.
BEARING, ROLLER - A bearing in which the relatively moving parts are separated by
rollers.
BEARING, RUBBING - A bearing in which the relatively moving parts slide without
deliberate lubrication.
BEARING, SELF-ALIGNING - A roller-element bearing with one spherical raceway that
automatically provides compensation for shaft or housing deflection or misalignment.
BEARING, SELF-LUBRICATING - A bearing independent of external lubrication. These
bearings may be sealed for life after packing with grease or may contain self-lubricating
material.
BEARING, SLEEVE - A cylindrical plain bearing used to provide radial location for a shat,
which moves axially. Sleeve bearings consist of one or more layers of bearing alloys,
bonded to a steel backing.
BEARING, SLIDE - A bearing used or positioning a slide or for axial alignment of a long
rotating shaft.
BEARING, STEP - A plane surface bearing that supports the lower end of a vertical shaft.
BEARING, THRUST - A bearing in which the load acts in the direction of the axis of
rotation.
BEARING, TILTING PAD - A pad bearing in which the pads are free to take up a position at
an angle to the opposing surface according to the hydrodynamic pressure distribution over
its surface.
BEARING, TRUNNION - A bearing used as a pivot to swivel or turn an assembly.https://boilersinfo.com
BED - A mass of ion-exchange resin particles contained in a column.
BED DEPTH - The height of the resinous material in the column after the ion exchanger
has been properly conditioned for effective operation.
BED EXPANSION - The effect produced during backwashing when the resin particles
become separated and rise in the column. The expansion of the bed due to the increase in
the space between resin particles may be controlled by regulating backwash flow (typical
with water treatment).
BELLOWS - Corrugated cylindrical container which moves as pressures change, or provides
a seal during movement of parts.
BELLOWS SEAL - A type of mechanical seal that utilizes a bellows for providing secondary
sealing.
BENDING MOMENT - The algebraic sum of the couples or the moments of the external
forces, or both, to the left or right of any section on a member subjected to bending by
couples or transverse forces, or both.
BERNOULLI'S THEOREM - In stream of liquid, the sum of elevation head, pressure head
and velocity remains constant along any line of flow provided no work is done by or upon
liquid in course of its flow, and decreases in proportion to energy lost in flow.
BICACARBONATE ALKALINITY - The presence in a solution of hydroxyl (OH-) ions resulting
from the hydrolysis of carbonates or bicarbonates. When these salts react with water, a
strong base and a weak acid are produced, and the solution is alkaline.
BICARBONATE - An ion or salt of carbonic acid, containing hydrogen, carbon, and oxygen
(HC03), such as sodium bicarbonate, NaHC03.
BIMETAL STRIP - Temperature regulating or indicating device which works on principle
that two dissimilar metals with unequal expansion rates, welded together, will bend as
temperatures change.
BIMETALLIC COUPLE - A joint or union of two dissimilar metals.
BIMETALLIC ELEMENT -
BIOCIDE - A chemical used to control the population of troublesome microbes.
BLACK LIQUOR - The liquid material remaining from pulpwood cooking in the soda or
sulfate papermaking process.
BLADE CLEARANCE (STEAM TURBINE) - Reaction turbine - the gap between blade and
casing. Impulse turbine - the gap between the stationary and moving blades.
BLAST FREEZER - Low-temperature evaporator which uses a fan to force air rapidly over
the evaporator surface.
BLAST FURNACE GAS - Is the waste product from furnaces used to smelt iron ores.
BLEEDER VALVE - A valve designed to slowly relief a liquid or gas form system.
BLEEDING - Slowly reducing the pressure of liquid or gas from a system or cylinder by
slightly opening a valve.https://boilersinfo.com
BLEEDOFF - The continuous removal of water from a re-circulating water system.
BLEEDOFF RATE - The rate at which water is continuously removed from a system.
BLOWDOWN - In connection with boilers or cooling towers, the process of discharging a
significant portion of the aqueous solution in order to remove accumulated salts, deposits
and other impurities.
BOILER - Closed container in which a liquid may be heated and vaporized.
BOILER FEED WATER - The total water fed to a boiler producing steam. This water is the
mixture of return steam condensate and makeup water.
BOILER HORSEPOWER - The work required to evaporate 34.5 lb of water per hour into
steam from and at 100°C.
BOILER LAY-UP - Storing and protecting the boiler when not in use.
BOILING - (See vaporization)
BOILING OUT - The boiling of high alkaline water in boiler pressure parts for the removal
of oil, greases, prior to normal operation or after major repairs.
BOILING POINT - The temperature at which the vapor pressure of a liquid equals the
absolute external pressure at the liquid-vapor interface.
BOILING TEMPERATURE - Temperature at which a fluid changes from a liquid to a gas.
BORE - Inside diameter of a cylinder.
BOURDON TUBE - Thin-walled tube of elastic metal flattened and bent into circular shape,
which tends to straighten as pressure inside is increased. Used in pressure gauges.
BOYLES' LAW - If the temperature on a gas is constant, the volume is inversely
proportional to the pressure. By formula - VP = V1P1
BRANCH CIRCUIT - Wiring between the last over current device and the branch circuit
outlets.
BRASS - A copper-zinc alloy containing up to 40% zinc and some smaller amounts of other
metals.
BRAYTON CYCLE (also referred to as the Joule Cycle) - A rotating machine in which
compression and expansion take place. Gas turbine are such an example.
BRAZE - A weld produced by heating an assembly to suitable temperatures and by using a
filler metal having a liquid us above 450°C. The filler metal is distributed between the
closely fitted facing surface of the joint by capillary action.
BRAZING, BLOCK - A brazing process in which the heat required is obtained from heated
blocks applied to the parts to be joined.
BREAKTHROUGH - The first appearance in the solution flowing from an ion-exchange unit
of unabsorbed ions similar to those which are depleting the activity of the resin bed.
Breakthrough is an indication that regeneration of the resin is necessary.
BRINE - Water saturated with a chemical such as salt.https://boilersinfo.com
BRITISH THERMAL UNIT, (BTU) - The Btu is defined as the heat required to raise the
temperature of a pound of water from 59° to 60°F.
BRITTLENESS - The tendency of a material to fracture without first undergoing significant
plastic deformation.
BRONZE - A copper-rich copper tin alloy with or without small proportions of other
elements.
BTU - British Thermal Unit. Is the measure of heat energy.
BUFFER - A substance used in solution, which accepts hydrogen ions or hydroxyl ions,
added to the solution as acids or alkali’s, minimizing a change in pH.
BULB - The name given to the temperature-sensing device located in the fluid for which
control or indication is provided. The bulb may be liquid-filled, gas filled, or gas-and-liquid
filled. Changes in temperature produce pressure changes within the bulb which are
transmitted to the controller.
BULGE - A local distortion or swelling outward caused by internal pressure on a tube wall
or boiler shell due to overheating.
BUS BAR - A heavy, rigid metallic conductor which carries a large current and makes a
common connection between several circuits. Bus bars are usually uninsulated and located
where the electrical service enters a building; that is, in the main distribution cabinet.
BYPASS - A pipe or duct, usually controlled by valve or damper, for conveying a fluid
around an element of a system.
BYPASS - Passage at one side of, or around, a regular passage.
BYPASS FEEDER - A closed tank that is installed in a system in "bypass," that is, in a side
stream taken off the system and leading back to the system rather than directly in-line.
Carnot Cycle - The most efficient heat engine cycle is the Carnot cycle, consisting of
two isothermal processes and two adiabatic processes. The Carnot cycle can be thought of
as the most efficient heat engine cycle allowed by physical laws
CALCAREOUS COATING OR DEPOSIT - A layer consisting of a mixture of calcium carbonate
and magnesium hydroxide deposited on surfaces being cathodically protected against
corrosion, because of increased pH adjustment to the protected surface.
CO - Carbon monoxide (CO) is a colorless, odorless, poisonous gas. It is produced by the
incomplete burning of solid, liquid, and gaseous fuels. Appliances fueled with natural gas,
liquefied petroleum (LP gas), oil, kerosene, coal, or wood may produce CO. Burning
charcoal produces CO. Running cars produce CO
CO2 - is an atmospheric gas composed of one carbon and two oxygen atoms. Carbon
dioxide results from the combustion of organic matter if sufficient amounts of oxygen are
present. It is also produced by various microorganisms in fermentation and is breathed out
by animals. Plants absorb carbon dioxide during photosynthesis, using both the carbon
and the oxygen to construct carbohydrates. It is present in the Earth's atmosphere at a
low concentration and acts as a greenhouse gas. It is a major component of the carbon
cycle.https://boilersinfo.com
CALCIUM - A scale forming element found in boiler feedwater.
CALCIUM CHLORIDE - A substance used to obtain calcium chloride brine.
CALCIUM SULFATE - Chemical compound (CaSO4) which is used at a drying agent or
desiccant in liquid line dryers.
CALIBRATION - A process of dividing and numbering the scale of an instrument; also of
correcting or determining the error of an existing scale, or of evaluating one quantity in
terms of readings of another.
CALORIE - It is equal to the amount of heat required to raise the temperature of one gram
of water one degree Celsius.
CALORIMETER - Device used to measure quantities of heat or determine specific heats.
CHANGE OF STATE - Change from one phase, such as solid, liquid or gas, to another.
CAPACITANCE - The property of an electric current that permits the storage of electrical
energy in an electrostatic field and the release of that energy at a later time.
CAPACITOR, (CONDENSER) - A device that can store an electric charge when voltage is
applied.
CAPACITY - The adsorption activity possessed in varying degrees by ion-exchange
materials. This quality may be expressed as kilograms per cubic foot, gram
milliequivalents per gram, pound-equivalents per pound, gram-milliequivalents per
milliliter, and so on, where the numerators of these ratios represent the weight of the ions
adsorbed and the denominators represent the weight or volume of the adsorbent.
CAPILLARY - The name given to the thin tube attached to the bulb which transmits the
bulb pressure changes to the controller or indicator. The cross sectional area of the
capillary is extremely small compared to the cross section of the bulb so that the capillary,
which is usually outside of the controlled fluid, will introduce the smallest possible error in
the signal being transmitted from the bulb.
CAPILLARY TUBE - The capillary tube is a metering device made from a thin tube
approximately 0.5 to 6 metre long and from 0.025 to 0.090 inches in diameter which feeds
liquid directly to the evaporator. Usually limited to systems of 1 ton or less, it performs all
of the functions of the thermal expansion valve when properly sized.
CARBON DIOXIDE - Compound of carbon and oxygen (CO2) which is sometimes used as a
refrigerant. Refrigerant number is R-744.
CARBON FILTER - Air filter using activated carbon as air cleansing agent.
CARBON RINGS - To minimize steam leakage, gland sealing arrangement features an
angle-type, carbon ring design with a packing case that is an integral part of the turbine
case. Inconel springs hold the rings in place.
CARBON TETRACHLORIDE - Colorless nonflammable and very toxic liquid used as a
solvent. It should never be allowed to touch skin and fumes must not be inhaled.
CARBONACEOUS EXCHANGER - Ion-exchange materials of limited capacity prepared by
the sulfonation of coal, lignite, peat, and so on.https://boilersinfo.com
CARBONATE - An ion or salt of carbonic acid, containing carbon and oxygen such as
calcium carbonate. (CaC03)
CARBONATE HARDNESS - That hardness caused in water by bicarbonates and carbonates
of calcium, and magnesium.
CARBONATE-POLYMER TREATMENT - A treatment method using synthetic polymers,
generally used with high hardness (60-70) ppm and high alkalinity.
CARBOXYLIC - A term describing a specific acidic group (COOH) that contributes cat ion
exchange ability to some resins.
CARRYOVER - The moisture and entrained solids forming the film of steam bubbles, as a
result of foaming in a boiler. This condition is caused by a faulty boiler water condition.
See also foaming.
CASCADE - A series of stages in which the output of one stage is the input of the next
stage.
CASCADE SYSTEMS - Arrangement in which two or more refrigerating systems are used in
series; uses evaporator of one machine to cool condenser of other machine. Produces
ultra-low temperatures.
CATHODE - In electrolysis or electrochemical corrosion, a site on a surface where actions
in solution are neutralized by electrons to become elements that either plate out on the
surface or react with water to produce a secondary reaction.
CATHODE PROTECTION - A method of preventing corrosion by making the metal a cathode
in a conducting medium by means of a direct electrical current that is galvanic.
CATHODIC PROTECTION - Reduction of corrosion rate by shifting the corrosion potential of
the electrode towards less oxidizing potential by applying an external electromotive force.
CATION - A positively charged ion that migrates through the electrolyte toward the
cathode under the influence of a potential gradient.
CATION-EXCHANGE SOFTENERS - Ion exchange units are known primarily as water
softeners. But they can also remove nitrates, sulfates, and various toxic metals from
water. ion exchangers. PDF
CATIONIC - The condition of a polymer, colloid, or large particle having exchangeable
anions on its surface and an opposite, positive charge on the substrata.
CAUSTIC CRACKING - A form of stress-corrosion cracking most frequently encountered in
carbon steels or iron-chromium-nickel alloys that are exposed to concentrated hydroxide
solutions at temperature of 200 to 250°C.
CAUSTIC EMBRITTLEMENT - An obsolete term replaced by caustic cracking.
CAUSTIC SODA - A common water treatment chemical, sodium hydroxide.
CAVITATION - The formation and collapse, within a liquid, of cavities or bubbles that
contain vapor or gas or both. In general, cavitation originates from decreases in static
pressure in the liquid. In order to erode a solid surface by cavitation, it is necessary for the
cavitation bubbles to collapse on or close to that surface.https://boilersinfo.com
CAVITATION EROSION - Progressive loss of original material from a solid surface due to
continuing exposure to cavitation.
CELSIUS TEMPERATURE SCALE - A thermometric scale in which the freezing point of water
is called 0°C and its boiling point 100°C at normal atmospheric pressure.
CENTANE NUMBER - A measure of ignition quality of a fuel or petroleum with reference to
normal centane high-ignition quality fuel with an arbitrary number of 100.
CENTRIFUGAL COMPRESSOR - Pump which compresses gaseous fluids by centrifugal force.
CENTRIFUGAL FORCE - is actually not a force but the experience of an inertial force
experienced in a rotating reference frame acting away from the center of the rotation. It is
equal in magnitude but opposite to the centripetal force required to constrain the body to
move in a circular motion. s actually not a force but the experience of an inertial.
CENTRIFUGAL FORCE -On a centrifugal pump, it is that force which throws water from a
spinning impeller.
CENTRIFUGAL PUMP - A pump consisting of an impeller fixed on a rotating shaft and
enclosed in a casing, having an inlet and a discharge connection. The rotating impeller
creates pressure in the liquid by the velocity derived from centrifugal force.
CENTRIFUGAL PUMP - Pump which produces fluid velocity and converts it to pressure
head.
Centripetal force - is the force that causes an object to move in a circle, acting
towards the centre of the circle. In the case of a satellite the centripetal force is gravity, in
the case of an object at the end of a rope, the centripetal force is the tension of the rope.
CHANGE OF STATE - Condition in which a substance changes from a solid to a liquid or a
liquid to a gas caused by the addition of heat. Or the reverse, in which a substance
changes from a gas to a liquid, or a liquid to a solid, caused by the removal of heat.
CHANNELING - Cleavage and furrowing of the bed due to faulty operational procedure, in
which the solution being treated follows the path of least resistance, runs through these
furrows, and fails to contact active groups in other parts of the bed, (water treatment).
CHARGE - Amount of refrigerant placed in a refrigerating unit.
CHARGING BOARD - Specially designed panel or cabinet fitted with gauges, valves and
refrigerant cylinders used for charging refrigerant and oil into refrigerating mechanisms.
CHECK VALVE - Device which permits fluid flow in one direction.
CHELATE - Is a molecule, similar to an ion exchanger, capable to withdraw ions from their
water solutions into soluble complexes.
CHEMICAL CLEANING - Using a solvent solution to remove mill scale and corrosion
products.
CHEMICAL FEEDLINE - The line which feeds the boiler treatment chemicals into the boiler.
CHEMICAL PRECIPITATION - When the chemicals react with the dissolved minerals in the
water to produce a relative insoluble reaction product. A typical example of this takes
place with the lime-soda softening process.https://boilersinfo.com
CHEMICAL REFRIGERATION - System of cooling using a disposable refrigerant. Also called
an expendable refrigerant system.
CHEMICAL STABILITY - Resistance to chemical change which ion-exchange resins must
possess despite contact with aggressive solutions.
CHILL FACTOR - Calculated number based on temperature and wind velocity.
CHILLED-WATER SYSTEM - A re-circulating water system using water chilled in a
refrigeration machine as a source for cooling.
CHILLER/HEATERS - A unit that supplies either chilled water for cooling or hot water for
heating, (HVAC).
CHLORIDE - An ion, compound, or salt of chlorine, such as sodium chloride (NaCl) or
calcium chloride (CaCl2).
CHLORINATION - A process in which chlorine gas or other chlorine compounds are added
to the water for the purpose of disinfecting.
CHOKE TUBE - Throttling device used to maintain correct pressure difference between
high-side and low-side in refrigerating mechanism. Capillary tubes are sometimes called
choke tubes.
CHORDAL THERMOCOUPLE - A thermocouple installed in furnace tubes, designed to
measure the effectiveness of water treatment within the boiler.
CIRCUIT - An electrical arrangement requiring a source of voltage, a closed loop of wiring,
an electric load and some means for opening and closing it.
CIRCUIT BREAKER - A switch-type mechanism that opens automatically when it senses an
overload (excess current).
CLAY - Finely suspended earth mineral sometimes found as an impurity in water.
CLEARANCE SPACE - Space between top of piston and the valve plate.
CLEARANCE VAPOR - The vapor remaining in the clearance space at the end of each
discharge stroke.
CLOSED CYCLE - is the gas turbine arrangement, in which the exhaust is directed back
again to compressor without coming in contact with the atmospheric air.
CLOSED FEED WATER HEATER - An indirect-contact feed water heater. Steam and water
are separated by tubes.
CLOSED RE-CIRCULATING WATER SYSTEM - A system using as a heat-transfer medium
water that continuously circulates through closed piping and heat exchanger without
evaporation.
CO COAGULANT - A substance that promotes the clumping of particulate matter in water,
forming a larger mass and thus promoting settling of particulates and clarification of the
water.
COAGULATION - Is the process whereby finely divided particles of turbidity and color,
capable of remaining in suspension indefinitely, are combined by chemical means into
masses sufficiently large to effect rapid settling.https://boilersinfo.com
COALESCENCE - The gathering together of coagulated colloidal liquids into a single
continuous phase.
CODE INSTALLATION - Refrigeration or air conditioning installation which conforms to the
local code and/or the national code for safe and efficient installations.
CO-EFFICIENT OF CONDUCTIVITY - Measure of the relative rate at which different
materials conduct heat. Copper is a good conductor of heat and, therefore, has a high
coefficient of conductivity.
COEFFICIENT OF EXPANSION - A measure of the change in length or volume of an oject,
specifically, a change measured by the increase in length or volume of an object per unit
length or volume.
COEFFICIENT OF FRICTION - The dimensionless ratio of the friction force (F) between two
bodies to the normal force (N) pressing these bodies together - (f) = (F/ N)
COEFFICIENT OF PERFORMANCE (COP) - Ratio of work performed or accomplished as
compared to the energy used under designated operating conditions.
COEFFICIENT OF THERMAL EXPANSION - The fractional change in length (or sometimes in
volume, when specified) of a material for a unit change in temperature.
COGENERATION - A term used to describe the combination of different thermodynamic
cycles for the purpose of increasing all-over cycle efficiency.
CO-GENERATION GENERATION - a term applied to identify the generation of people
interested in co-generation.
COLD - The absence of heat; a temperature considerably below normal.
COLD DECK -The cooling section of a mixed air zoning system.
COLD JUNCTION - That part of a thermoelectric system which absorbs heat as the system
operates.
COLD PROCESS - A water treatment process carried out at room temperature.
COLD WALL - Refrigerator construction which has the inner lining of refrigerator serving as
the cooling surface.
COLLOIDAL - A state of suspension in a liquid medium in which extremely small particles
are suspended and dispersed but not dissolved.
COLLOIDS - Organic matter of very fine particle size, usually in the range of 10-5 to 10-7
cm in diameter. It tends to inhibit the formation of dense scale and results in the
deposition of sludge, or causes it to remain in suspension, so that it may be blown from
the boiler.
COLUMN OPERATION - Conventional utilization of ion-exchange resins in columns through
which pass, either upflow or down flow, the solution to be treated.
COMBINED FEEDER CUTOFF - A device that regulates makeup water to a boiler in
combination with a low-water fuel cutoff.
COMBINED STEAM-GAS PLANT - where a gas turbine is combined with steam plant in
order to utilize the waste heat.https://boilersinfo.com
COMBINED TREATMENT - A method of physical treatment , followed by the addition of
chemicals to remove oxygen.
COMBUSTION - The act or process of burning.
COMFORT CHART - A chart showing effective temperatures with dry-bulb temperatures
and humidity's (and sometimes air motion) by which the effects of various air conditions
on human comfort may be compared.
COMFORT COOLER - System used to reduce the temperature in the living space in homes.
These systems are not complete air conditioners as they do not provide complete control
of heating, humidifying, dehumidification, and air circulation.
COMFORT COOLING - Refrigeration for comfort as opposed to refrigeration for storage or
manufacture.
COMFORT ZONE - (Average) the range of effective temperatures over which the majority
(50 percent or more) of adults feels comfortable; (extreme) the range of effective
temperatures over which one or more adults feel comfortable. An area on the
psychometric chart which shows conditions of temperature, humidity and sometimes air
movement in which most people are comfortable.
COMMON NEUTRAL - A neutral conductor that is common to, or serves, more than one
circuit.
COMPOSITION - The elements or chemical components that make up a material and their
relative proportions.
COMPOUND - They are chemically combined elements with definite proportions of the
component elements.
COMPOUND GAUGE - Instrument for measuring pressures both above and below
atmospheric pressure.
COMPOUND REFRIGERATING SYSTEMS - System which has several compressors or
compressor cylinders in series. The system is used to pump low pressure vapors to
condensing pressures.
COMPRESSION - Term used to denote increase of pressure on a fluid by using mechanical
energy.
COMPRESSION RATIO - Ratio of the volume of the clearance space to the total volume of
the cylinder. In refrigeration it is also used as the ratio of the absolute low-side pressure
to the absolute high-side pressure.
COMPRESSION, ADIABATIC - Is compressing a gas without removing or adding heat.
COMPRESSOR - Pump of a refrigerating mechanism which draws a low pressure on cooling
side of refrigerant cycle and squeezes or compresses the gas into the high-pressure or
condensing side of the cycle.
COMPRESSOR - The pump which provides the pressure differential to cause fluid to flow
and in the pumping process increases pressure of the refrigerant to the high side
condition. The compressor is the separation between low side and high side.
COMPRESSOR DISPLACEMENT - Volume, in cubic inches, represented by the area of the
compressor piston head or heads multiplied by the length of the stroke.https://boilersinfo.com
COMPRESSOR SEAL - Leak proof seal between crankshaft and compressor body in open
type compressors.
COMPRESSOR SURGING - An instability of air flow with axial compressor on the first
stages of these compressors. Air flow might even be reversed that point.
COMPRESSOR TURBINE - in terms of a gas turbine arrangement, it is the turbine which
drives the compressor only.
COMPRESSOR, CLEARANCE POCKET - Small space in a cylinder from which compressed
gas is not completely expelled. This space is called the compressor clearance space or
pocket. For effective operation, compressors are designed to have as small a clearance
space as possible.
COMPRESSOR, ROTARY BLADE - Mechanism for pumping fluid by revolving blades inside
cylindrical housing.
COMPRESSOR, SINGLE-STAGE - Compressor having only one compressive step between
low-side pressure and high-side pressure.
COMPRESSIBILITY - The ease which a fluid may be reduced in volume by the application
of pressure, depends upon the state of the fluid as well as the type of fluid itself.
CONDENSATE - The liquid formed by condensation of a vapor. In steam heating, water
condensed from steam; in air conditioning, water extracted from air, as by condensation
on the cooling coil of a refrigeration machine.
CONDENSATE POLISHER - A device used to clean the returning condensate to the boiler
feedwater system.
CONDENSATE PUMP - Device to remove water condensate that collects beneath an
evaporator.
CONDENSATION - Process of changing a vapor into liquid by extracting heat.
Condensation of steam or water vapor is effected in either steam condensers or
dehumidifying coils, and the resulting water is called condensate.
CONDENSE - Action of changing a gas or vapor to a liquid.
CONDENSER - An apparatus used to transfer heat from a hot gas, simultaneously reducing
that gas to a liquid.
CONDENSER TUBE - The heat transfer surface in a condenser.
CONDENSER-WATER SYSTEM - A re-circulating cooling water used as a heat transfer fluid
for the condensation of a gas.
CONDENSING BLEEDER TURBINE -
CONDENSING TEMPERATURE - The temperature at which the condensing gas is returned
to a liquid at the same pressure.
CONDENSING TURBINE - With this turbine, the steam exhausts to the condenser and the
latent heat of the steam is transferred to the cooling water. The condensed steam is
returned to the boiler as feedwater.https://boilersinfo.com
CONDENSING UNIT - Part of a refrigerating mechanism which pumps vaporized refrigerant
from the evaporator, compresses it, liquefies it in the condenser and returns it to the
refrigerant control.
CONDENSING UNIT SERVICE VALVES - Shutoff valves mounted on condensing unit to
enable service technicians to install and/or service unit.
CONDENSING UNIT, REFRIGERANT - An assembly of refrigerating components designed to
compress and liquefy a specific refrigerant, consisting of one or more refrigerant
compressors, refrigerant condensers, liquid receivers (when required) and regularly
furnished accessories.
CONDUCTANCE, ELECTRICAL - The reciprocal (opposite) of resistance and is the current
carrying ability of any wire or electrical component. Resistance is the ability to oppose the
flow of current.
CONDUCTANCE, SURFACE FILM - Time rate of heat flow per unit area under steady
conditions between a surface and a fluid for unit temperature difference between the
surface and fluid.
CONDUCTION - Transfer of heat by direct contact.
CONDUCTIVITY (ELECTRICAL) - The ability of a liquid to conduct an electrical current and
indicating the presence of cat ions and anions. Conductivity is usually expressed in
Micromos per cm.
CONDUCTIVITY (THERMAL) - The time rate of heat flow through unit thickness of an
infinite slab of homogeneous material in a direction perpendicular to the surface, induced
by unit temperature difference. (W/m K)
CONDUCTIVITY METER - An electric instrument used to measure the conductivity of water
to determine its content of dissolved solids.
CONDUCTIVITY, THERMAL - The time rate of heat flow through unit area and unit
thickness of a homogeneous material under steady conditions when a unit temperature
gradient is maintained in the direction perpendicular to area. Materials are considered
homogeneous when the value of the thermal conductivity is not affected by variation in
thickness or in size
CONDUCTOR - Substance or body capable of transmitting electricity or heat.
CONDUIT - A round cross-section electrical raceway, of metal or plastic.
CONGEALER - Also known as freezer.
CONGRUENT PHOSPHATE CONTROL - Similar as a coordinated phosphate control but more
restrictive where the equilibrium is based on maintaining a ratio of 2.6 Na/1.0 PO4, instead
of 3.0/1.0 PO4.
CONNECTED LOAD - The sum of all loads on a circuit. (1) Connection in Parallel: System
whereby flow is divided among two or more channels from a common starting point or
header. (2) Connection in Series: System whereby flow through two or more channels is in
a single path entering each succeeding channel only after leaving the first or previous
channel.
CONSTRICTOR - Tube or orifice used to restrict flow of a gas or a liquid.https://boilersinfo.com
CONTAMINATION - The introduction into water of microorganisms, chemicals, toxic
materials, waste water in a concentration that makes the water unfit for its next intended
use.
CONTROL - A device for regulation of a system or component in normal operation, manual
or automatic. If automatic, the implication is that it is responsive to changes of pressure,
temperature or other property whose magnitude is to be regulated.
CONTROL POINT - The value of the controlled variable which the controller operates to
maintain.
CONTROL VALVE - Valve which regulates the flow or pressure of a medium which affects a
controlled process. Control valves are operated by remote signals from independent
devices using any of a number of control media such as pneumatic, electric or electro
hydraulic.
CONTROLLED DEVICE - One which receives the converted signal from the transmission
system and translates it into the appropriate action in the environmental system. For
example: a valve opens or closes to regulate fluid flow in the system.
CONTROLLER - A device capable of measuring and regulating by receiving a signal from a
sensing device, comparing this data with a desired value and issuing signals for corrective
action.
CONVECTION - The movement of a mass of fluid (liquid or gas) caused by differences in
density in different parts of the fluid; the differences in density are caused by differences
in temperature. As the fluid moves, it carries with it its contained heat energy, which is
then transferred from one part of the fluid to another and from the fluid to the
surroundings.
CONVECTION, FORCED - Convection resulting from forced circulation of a fluid, as by a
fan, jet or pump.
CONVECTION, NATURAL - Circulation of gas or liquid (usually air or water) due to
differences in density resulting from temperature changes.
CONVERGENT NOZZLE - Impulse Turbine - Stationary convergent nozzles are used for
smaller pressure drops where the minimum exit pressure is 0.577 x the inlet pressure (the
critical pressure for nozzles.) If the exit pressure is less than 0.577 x inlet pressure, eddy
currents are developed and the exit velocity will be less than calculated.
CONVERGENT-DIVERGENT NOZZLE - Impulse Turbine - Stationary convergent-divergent
nozzles prevent eddy-currents and the calculated velocity will be obtained even at large
pressure drops.
COOLER - Heat exchanger which removes heat from a substance.
COOLING EFFECT, SENSIBLE - The difference between the total cooling effect and the
dehumidifying effect, usually in watts.
COOLING EFFECT, TOTAL - Difference between the total enthalpy of the dry air and water
vapor mixture entering the cooler per hour and the total enthalpy of the dry air and water
vapor mixture leavir~ the cooler per hour, expressed in watts.
COOLING TOWER - Device for lowering the temperature of water by evaporative cooling,
in which water is showered through a space through which outside air circulates. A portion https://boilersinfo.com
of the water evaporates, its latent heat of vaporization cooling that portion of the water
which does not evaporate.
COOLING, EVAPORATIVE - Involves the adiabatic exchange of heat between air and water
spray or wetted surface. The water assumes the wet-bulb temperature of the air, which
remains constant during its traverse of the exchanger.
COOLING, REGENERATIVE - Process of utilizing heat which must be rejected or absorbed
in one part of the cycle to function usefully in another part of the cycle by heat transfer.
COORDINATED PHOSPHATE CONTROL A treatment to prevent caustic gauging. Free
caustic is eliminated by maintaining an equilibrium between the sodium and phosphate.
Control is based on maintaining a ratio of 3.0 Na to/1.0 PO4.
CORRATOR - A device or probe employed to measure current flow in a process flow. It
consists of two identical electrodes, to which a small current is applied and measured,
from which corrosion rates can be calculated.
CORROSION - The chemical or electrochemical reaction between a material, usually a
metal, and its environment that produces a deterioration of the material and its properties.
CORROSION, ANODE - The dissolution of an metal acting as an anode.
CORROSION, ATMOSPHERIC - The gradual degradation or alteration of a material by
contact with substances present in the atmosphere, such as oxygen, carbon dioxide, water
vapor, and sulfur and chlorine compounds.
CORROSION, BIOLOGICAL - Deterioration of metals as a result of the metabolic action of
microorganisms. Also often named fouling.
CORROSION, CATHODIC - Corrosion resulting resulting from a cathodic condition of a
structure usually caused by the reaction of an amphoteric metal with the alkaline products
of electrolysis.
CORROSION, CAVITATION - A process involving conjoint corrosion and cavitation.
CORROSION, CONCENTRATION ATTACK - A form of corrosion caused by the concentration
of caustic or phosphate salts under porous deposits, generally iron oxide. Sometimes
found at welded tubes and due to steam blanketing.
CORROSION, CONCENTRATION-CELL - Pitting type of corrosion caused by an electrical
potential differential between surfaces of a metal as a result of deposits or differences in
the solution concentration in contact with the metal.
CORROSION, COUPONS - Pre-weighed metal strips installed into fluid systems for the
purpose of monitoring metal losses.
CORROSION, CREVICE - Localized corrosion of a metal surface at, or immediately adjacent
to an area that is shielded from full exposure to the environment because of close
proximity between metal and the surface of another metal.
CORROSION, DEACTIVASION - The process of prior removal of the active corrosive
constituents, usually oxygen, from a corrosive liquid by controlled corrosion of expendable
metal or by other chemical means, therby making the liquids less corrosive.
CORROSION, DEPOSIT (also called poultice corrosion) - Corrosion occuring under or
around a discontinous deposit on a metallic surface.https://boilersinfo.com
CORROSION, EFFECT - A change in any part of the corrosion system caused by corrosion.
CORROSION, ELECTROCHEMICAL - Corrosion that is accompanied by a low of electrons
between cathodic and anodic areas on metallic surfaces.
CORROSION, EMBRITTLEMENT - The severe loss of ductility of a metal resulting from
corrosive attack, usually intergranular and often not visible.
CORROSION, EXTERNAL - A chemical deterioration of the metal on the fireside of boiler
heating surfaces.
CORROSION, FATIGUE - The process in which a metal fractures prematurely under
conditions of simultaneous corrosion and repeated cyclic loading at lower stress levels or
fewer cycles than would be required in the absence of the corrosive environment.
CORROSION, FILIFORM - Corrosion that occurs under organic coatings on metals as fine
wavy hairlines.
CORROSION, FRETTING - A type of corrosion which occurs where metals slide over each
other. Long tubes in heat exchangers often vibrate, causing metal to metal contact, tube
supports etc.. The metal to metal rubbing causes mechanical damage to the protective
oxide coating.
CORROSION, GALVANIC - Corrosion of a metal caused by its contact with a metal of lower
activity; this contact results in an electron flow or current and dissolution of one of the
metals.
CORROSION, GASEOUS - Corrosion with gas as the only corrosive agent and without any
aqueous phase on the surface of the metal. Also called dry corrosion.
CORROSION, GENERAL - A form of deterioration that is distributed more or less uniformly
over a surface.
CORROSION, GRAPHITIC - Corrosion of grey iron in which the iron matrix is selectively
leached away, leaving a porous mass of graphite behind. This type of corrosion occurs in
relativel mild aquous solutions and on buried piping.
CORROSION, HOT - An accelerated corrosion of metal surfaces that results from the
combined effect of oxidation and ractions with sulfur compounds or other contminants
such as chlorides, to form a molten salt on a metal surface that fluxes, destroys or
disrupts the normal protective oxide. (commonly found in pulp mills)
CORROSION, IMPINGEMENT - A form of erosion-corrosion generally associated with local
impingement of a high velocity, flowing fluid against a solid surface.
CORROSION, INFLUENCED - The corrosion cause by organisms due to their discharge
containing sulfur compounds and the depolarization with other types of discharge due to
the presence of the microorganisms.
CORROSION, INHIBITORS - Substances that slow the rate of corrosion.
CORROSION, INTERCRYSTALINE -(see intergranular cracking)
CORROSION, INTERGRANULAR - Localized attack occurring on the metal grain boundaries.
This is commonly found with stainless steels which have been improperly heat treated.CORROSION, INTERNAL - Usually refers to the internal corrosion and is considered an
electrochemical deterioration of the boiler surface at or below the water surface.
CORROSION, LOCALIZED - Corrosion at discrete sites, for example, crevice corrosion,
pitting, and stress-corrosion cracking.
CORROSION, LOCALIZED - Non-uniform corrosion of a metal surface highlighted by spotty
or pitting-type corrosion.
CORROSION, MICROBIAL - (see biological corrosion).
CORROSION, OXYGEN DEFICIENCY - A form of crevice corrosion in which galvanic
corrosion proceeds because oxygen is prevented from diffusing into the crevice.
CORROSION, POTENTIAL - The voltage between a corroding metal and a reference
electrode.
CORROSION, POULTICE - (see corrosion, deposit)
CORROSION, POULTICE - A term used in the automotive industry to describe the corrosion
of vehicle body parts due to the collection of road salts and debries on ledges and in
pockets that are kept moist by weather and washing.
CORROSION, PROTECTION - Modification of a corrosion system so that corrosion damage
is mitigated.
CORROSION, RESISTANCE - The ability of a material to resist deterioration by chemical or
electrochemical reaction with its environment.
CORROSION, STRAY CURRENT - A form of attack caused by electrical currents going
through unintentional path.
CORROSION, STRESS - Preferential attack of areas under stress in a corrosive
environment, where such a environment alone would not have caused corrosion.
CORROSION, STRESS CORROSION CRACKING - Material deterioration due to cracking, by
being under static stress either applied or residual.
CORROSION, SWEET - The deterioration of metal caused by contact with carbon dioxide in
water.
CORROSION, THERMO-GALVANIC - Corrosion resulting from an electrochemical cell
caused by a thermal gradient.
CORROSION, UNIFORM - The simplest form of corrosion. It attacks all surfaces exposed to
a corrodent.
CORROSIVE WEAR - A material deterioration due to the co-joint action of corrosion and
mechanical action.
CORROSIVITY - An indication of the corrosiveness of the water of material. The corrosivity
of a water as described by the water’s pH, alkalinity, hardness, temperature, total
dissolved solids, dissolved oxygen concentration and the Langerier Index.
COUNTER-FLOW HEAT EXCHANGER - When the fluid to be cooled flows against the
direction of the coolant. In heat exchange between two fluids, opposite direction of flow,
coldest portion of one meeting coldest portion of the other.COVALENT BOND - A bond in which two atoms share pair of electrons.
CRANKSHAFT SEAL - Leak proof joint between crankshaft and compressor body.
CRAZE CRACKING (OR CHECKING) - Irregular surface cracking of metal associated with
thermal cycling.
CREEP - Time dependent permanent strain under stress. This is used to rate the resistance
of a material to plastic deformation under sustained load.
CREEP STRENGTH - The constant nominal stress that will cause a specified quantity of
creep in a given time at constant temperature. Creep strength is expressed as the stress
necessary to produce 0.1% strain in 1000 hours.
CREEP, DYNAMIC - Creep that occurs under conditions of fluctuating load or fluctuating
temperatures.
CRISPER - Drawer or compartment in refrigerator designed to provide high humidity along
with low temperature to keep vegetables, especially leafy vegetables - cold and crisp.
CRITICAL HUMIDITY - The relative humidity above which the atmospheric corrosion rate of
some metals increase sharply.
CRITICAL POINT - A point at which the saturated liquid and saturated vapor states are
identical. Also, the latent heat of evaporization is zero at this point.
CRITICAL PRESSURE - The pressure at the critical temperature above which the fluid no
longer has the properties of a liquid, regardless of further increase of pressure.
CRITICAL SPEED -
CRITICAL TEMPERATURE - That temperature above which the vapor phase cannot be
condensed to liquid by an increase in pressure.
CRITICAL VELOCITY - Maximum velocity is obtained and no further pressure drop is
obtained. (Acoustic Velocity).
CROSS COMPOUND TURBINE - These turbines are large turbines with parallel shafts with
a generator on each shaft. The steam flows through the high pressure turbine, then is
crossed-over to the low pressure turbine
CRT - Cathode ray tube terminal.
CRYOGENIC FLUID - Substance which exists as a liquid or gas at ultra-low temperatures -
157°C.
CRYOGENIC SUPERCONDUCTOR SYSTEM - Uses helium to cool conductors to within few
degrees of absolute zero where they offer no electric resistance.
CRYOGENICS - Refrigeration which deals with producing temperatures of -157°C below
zero and lower.
Crystal Formation, Zone of Maximum: Temperature range in freezing in which most
freezing takes place, i.e., about 25¡F to 30¡F for water.
CRYSTALLITES - Atoms arranged in a repeating and definite structure.CRYSTALLIZATION - The separation, usually from a liquid phase on cooling, of a solid
crystalline phase.
CURRENT (I) - The electric flow in an electric circuit, which is expressed in amperes
(amps).
CURRENT DENSITY - The current flowing to or from a unit area of an electrode surface.
CURTIS METHOD or Curtis stage - Velocity Compounding - This turbine design consists of
one set of nozzles in which the steam is expanded from initial to exhaust pressure. The
velocity of the steam resulting from this expansion is absorbed in two or more rows of
moving blades. Rows of fixed or guide blades, attached to the casing, are set between
rows of moving blades and receive and redirect the steam to the next row of moving
blades. As the velocity is absorbed in more than one row of moving blades, the blade
speed is less than if the velocity was all absorbed in one row of blades.
CYCLE - A series of thermodynamic processes during which the working fluid can be made
to undergo changes involving energy transition and is subsequently returned to its original
state.
CYCLE, REVERSIBLE - Theoretical thermodynamic cycle, composed of a series of reversible
processes, which can be completely reversed.
CYCLE, WATER TREATMENT - A complete course of ion-exchange operation. For instance,
a complete cycle of cation exchange would involve regeneration of the resin with acid,
rinse to remove excess acid, exhaustion, backwash, and finally regeneration.
CYCLES - A system that undergoes a series of processes and always returns to its initial
state.
CYCLES OF CONCENTRATION - The number of times the soluble mineral salts in a water
supply have been concentrated in, a system.
CYLINDER HEAD - Plate or cap which encloses compression end of compressor cylinder.
DALTON'S LAW OF PARTIAL PRESSURE - Each constituent of a mixture of gases behaves
thermodynamically as if it alone occupied the space. The sum of the individual pressures
of the constituents equals the total pressure of the mixture.
DAMPER - A device used to vary the volume of air passing through an air outlet, air inlet
or duct.
DASHPOT - A damping device, usually consisting of a cylinder and a piston in which
relative motion of either displaces a fluid such as air or oil, resulting in friction.
DEADBAND - In HVAC, a temperature range in which neither heating nor cooling is turned
on; in load management, a kilowatt range in which loads are neither shed nor restored.
DE-AERATING HEATERS - Mechanical device using steam to strip dissolve gases from the
boiler feedwater and heating the feedwater.
DE-AERATION - Act of separating air from substances.
DE-AERATOR - An apparatus or device which is used to remove dissolved air or oxygen
from water.DE-ALKALIZATION - The removal of alkalinity from a water supply by neutralization or ion
exchange.
DE-ALKALIZER - An apparatus or device used to remove the alkaline carbonate and
bicarbonate ions from a water supply.
DE-ALLOYING - This is a corrosion process whereby one constituent of a metal alloy is
preferentially removed from the alloy, leaving an altered residual microstructure.
DEASHING - The removal from a solution of inorganic salts by means of adsorption by ion
exchange resins of both the cations and the anions that comprise the salts. See
deionization.
DE-CARBONATION - Refers to the removal of carbon dioxide from the boiler feedwater.
DECIBEL (dB) - A decibel is a division of a logarithmic scale for expressing the ratio of two
quantities proportional to power or energy. The number of decibels denoting such a ratio is
ten times the logarithm of the
DECONCENTRATOR - This is a cylindrical tank connected before the boiler to receive the
boiler feedwater before entering the boiler. It is designed to promote settling of suspended
solids, which then could be removed via its own blowdown device. Was used for operation
with very high suspended solids.
DE-FLOCCULANT - An electrolyte adsorbed on colloidal particles in suspension that charges
the particles to create repulsion forces which maintain the particles in a dispersed state,
thus reducing the viscosity of the suspension.
DEFROST CYCLE - Refrigerating cycle in which evaporator frost and ice accumulation is
melted.
DEFROST TIMER - Device connected into electrical circuit which shuts unit off long enough
to permit ice and frost accumulation on evaporator to melt.
DEFROSTING - Process of removing frost accumulation from evaporators.
DEFROSTING CONTROL - Device to automatically defrost evaporator. It may operate by
means of a clock, door cycling mechanism or during "off" portion of refrigerating cycle.
DEFROSTING TYPE EVAPORATOR - Evaporator operating at such temperatures that ice and
frost on surface melts during off part of operating cycle.
DEGREE DAY - A unit, based upon temperature difference and time, used in estimating
fuel consumption and specifying nominal heating load of a building in winter. For any one
day, when the mean temperature is less than 65°F there exist as many degree days as
there are Fahrenheit degrees difference in temperature between the mean temperature for
the day and 65°F.
DEGREES OF SUPERHEAT - The amount by which the temperature of a superheated vapor
exceeds the temperature of the saturated vapor at the same pressure.
DEHUMIDIFICATION - The condensation of water vapor from air by cooling below the
dewpoint or removal of water vapor from air by chemical or physical methods.
DEHUMIDIFIER -(1) An air cooler or washer used for lowering the moisture content of the
air passing through it; (2) An absorption or adsorption device for removing moisture from
air. DEHUMIDIFYING - Removal of moisture from the air.
DEHYDRATION - The removal of water vapor from air, stored goods or refrigerants.
Deionization - Deionization, a more general term than deashing, embraces the removal of
all charged constituents or ionizable salts (both inorganic and organic) from solution.
DE-IONIZER - An apparatus or device used to remove the ions of dissolved salts from
water.
DEMAND - The probable maximum rate of water flow as determined by the number of
water supply fixture units.
DEMAND CHARGE - That part of an electric bill based on kW demand and the demand
interval, expressed in dollars per kilowatt. Demand charges offset construction and
maintenance of a utility's need for a large generating capacity.
DEMAND CONTROL - A device which controls the kW demand level by shedding loads
when the kW demand exceeds a predetermined set point.
DEMAND INTERVAL - The period of time during which kW demand is monitored by a utility
service, usually 15 or 30 minutes long.
DEMAND LOAD - The actual amount of load on a circuit at any time. The sum of all the
loads which are ON. Equal to the connected load minus the loads that are OFF.
DEMAND READING - Highest or maximum demand for electricity an individual customer
registers in a given interval, example, 15 minute interval. The metered demand reading
sets the demand charge for the month.
DEMINERALIZER - A process to remove dissolved matter from boiler pretreated water by
contacting the water with ion-exchange resins.
DENSITY - The ratio of the mass of a specimen of a substance to the volume of the
specimen. The mass of a unit volume of a substance. When weight can be used without
confusion, as synonymous with mass, density is the weight per unit volume.
DENSITY, ABSOLUTE - Mass per unit volume of a solid material, expressed usually in
kg/m3.
DESALINATION - The removal of inorganic dissolved solids from water.
DESICCANT, LIQUID - A hygroscopic liquid, such as glycol, used to remove water from
other fluids.
DESICCANT - Any absorbent or adsorbent, liquid or solid, that will remove water or water
vapor from a material. In a refrigeration circuit, the desiccant should be insoluble in the
refrigerant.
DESIGN PRESSURE - Highest or most severe pressure expected during operation.
Sometimes used as the calculated operating pressure plus an allowance for safety.
DESIGN PRESSURE - Highest or most severe pressure expected during operation.
Sometimes used as the calculated operating pressure plus an allowance for safety.
DESIGN WORKING PRESSURE - The maximum allowable working pressure for which a
specific part of a system is designed. DESILICIZER - An apparatus or device used to remove silica from a water supply.
DESSERT BAG - A canvas bag which permits seepage of its liquid. The liquid will evaporate
and obtains the to evaporate partly from the content of the bag and thus cooling its
content.
DESSERT BAG - A canvas bag which permits seepage of its liquid. The liquid will evaporate
and obtains the to evaporate partly from the content of the bag and thus cooling its
content.
DETERGENT ADDITIVE - In lubrication technology, a surface active additive that helps to
keep solid particles suspended in an oil
DETERGENT CLEANING - A boiler cleaning process using an alkaline solution, primarily to
remove oil and grease.
DETERGENT OIL - A heavy duty oil containing a detergent additive. These oils are mainly
used in combustion engines.
DETERGENT-DISPERSANT - A compound mixture of cleaning agents that have both
surface-active properties and suspending properties.
DEW POINT - Temperature at which vapor (at 100 percent humidity) begins to condense
and deposit as liquid.
DEW POINT DEPRESSION - The difference between dry bulb and dew point temperatures.
DEW POINT TEMPERATURE - The temperature at which condensation begins, if air is
cooled at constant pressure.
DIAPHRAGM - Flexible material usually made of thin metal, rubber or plastic.
DIATOMACEOUS EARTH FILTRATION - Is a process in which a filter cake or precoat of
diatomaceous earth is used as a filter medium.
DIELECTRIC - A nonconductor of electricity.
DIELECTRIC FITTING - A non conductive substance such as plastic that is placed between
two dissimilar metals to prevent galvanic current flow.
DIELECTRIC STRENGTH - A measure of the ability of a dielectric (insulator) to withstand a
potential difference across it without electric discharge.
DIFFERENTIAL - The temperature or pressure difference between cut-in and cut-out
temperature or pressure of a control.
DIFFERENTIAL AERATION CELL - An electrolytic cell, the electromagnetic force of which is
due to a difference in air (oxygen) concentration at one electrode as compared with that at
another electrode of the same material. (see concentration cell)
DIFFERENTIAL SOLUTE CONCENTRATION - A potential difference between an anode and
cathode on metal, because of a concentration cell due to dissolved metals.
DIFFUSER - A circular, square, or rectangular air distribution outlet, generally located in
the ceiling and comprised of deflecting members discharging supply air in various
directions and planes, and arranged to promote mixing of primary air with secondary room
air. DIRECT ACTING - Instruments that increase control pressure as the controlled variable
(such as temperature or pressure) increases; while reverse acting instruments increase
control pressure as the controlled variable decreases.
DIRECT CURRENT - A source of power for an electrical circuit which does not reverse the
polarity of its charge.
DIRECT-EXPANSION EVAPORATOR - One that contains only enough liquid to continue
boiling as heat is absorbed by it.
DISPERSANT - A chemical which causes particulates in a water system to remain in
suspension.
DISPERSANT OIL - A heavy duty oil containing a dispersant additive.
DISPLACEMENT PUMP - Pumps in which energy is added to the water periodically and the
water is contained in a set volume.
DISPLACEMENT VOLUME - The volume displaced by the piston between top dead center
and bottom dead center.
Dissociation - Ionization.
DISSOLVED GASES - Gases soluble in water.
DISSOLVED SOLIDS (TDS) - The measure of the total amount of dissolved matter.
DISTILLATION - Involves boiling water and condensing the vapor.
DMA - Direct memory access. A process where block of data can be transferred between
main memory and secondary memory without processor intervention.
DOMESTIC HOT WATER - Potable hot water as distinguished from hot water used for
house heating.
DOUBLE CASING (STEAM TURBINE) -
DOWEL PINS - Metal pins that guarantee exact alignment of a flange joint on a
horizontally split casing as found in turbine construction
Downflow - Conventional direction of solutions to be processed in ion-exchange column
operation, that is, in at the top, out at the bottom of the column.
DOWNSTREAM - The outlet side of an instrument, a pump, valve, etc..
DRAFT GAUGE - Instrument used to measure air movement by measuring air pressure
differences.
DRIER - Substance or device used to remove moisture from a refrigeration system.
DRIERITE - Desiccant which operates by chemical action.
DRIFT - Entrained water in the stack discharge of a cooling tower.
DRIFT - Term used to describe the difference between the set point and the actual
operating or control point. DROOP - Terms used to describe the difference between the set point and the actual
operating or control point.
DRUM WATER LEVEL LINE - The water level in the drum during the normal operating
mode.
DRY BULB - An instrument with a sensitive element to measure ambient air temperature.
DRY BULB TEMPERATURE - The temperature registered by an ordinary thermometer. The
dry bulb temperature represents the measure of sensible heat, or the intensity of heat.
DRY COMPRESSION - The compression of vapor, in a vapor-liquid vapor-compression
refrigeration cycle.
DRY ICE - Refrigerating substance made of solid carbon dioxide which changes directly
from a solid to a gas (sublimates). Its subliming temperature is -78°C.
DRY PIPE - A perforated or slotted pipe or box inside the drum and connected to the steam
outlet.
DRY STANDBY - A method of sealing al water and steam connections and placing a
desiccant in the unit and applying an airtight seal.
DRY SYSTEM - Refrigeration system which has the evaporator liquid refrigerant mainly in
the atomized or droplet condition.
DRYNESS FRACTION OR QUALITY - Weight fraction of the vapor in a vapor-liquid mixture.
DUAL SHAFT GAS TURBINE - a gas turbine which has one turbine on one shaft driving the
compressor and when the gas discharged from this turbine is directed to another turbine
on a separate shaft to drive a load.
DUAL-TEMPERATURE RE-CIRCULATING WATER SYSTEM - A closed re-circulating water
system that uses water either for cooling, by circulating it through a chiller, or for heating,
by circulating it through a boiler or heat-exchanger depending upon need.
DUCTILE GOUGING - Referring to irregular wasting of the tube metal beneath a porous
deposit The micro structure of the metal does not change with this process and the
ductility remains, but the thinning leads to rapture.
DUCTILITY - The ability of a material to deform plastically without fracturing.
DUMMY PISTON - The axial thrust in reaction turbines can be nearly eliminated by the use
of balance or dummy pistons. With the correct size of a dummy piston exposed to two
different bleed point pressures, the thrust is nearly equalized. There is a small leakage
across the labyrinth seal of the dummy piston as steam leaks from the high to the lower
bleed point
DUST - An air suspension (aerosol) or particles of any solid material, usually with particle
size less than 100 microns.
DYNAMIC DISCHARGE HEAD - Static discharge head plus friction head plus velocity head.
DYNAMIC LOAD - An imposed force that is in motion, that is, one that may vary in
magnitude, sense, and direction.DYNAMIC PUMPS - Pumps in which energy is added to the water continuously and the
water is not contained in a set volume.
DYNAMIC SUCTION HEAD - Positive static suction head minus friction head and minus
velocity head.
DYNAMIC SUCTION LIFT - The sum of suction lift and velocity head at the pump suction
when the source is below pump centerline.
DYNAMIC SYSTEM - An ion-exchange operation, wherein a flow of the solution to be
treated is involved.
ECONOMIZER - A series of tubes located in the path of flue gases. Feedwater is pumped
through these tubes on its way to the boiler in order to absorb waste heat from the flue
gas.
EDDY CURRENT TESTING - An electromagnetic nondestructive testing method in which
eddy-current flow is induced in the test object. Changes in flow caused by variations in the
object are deflected into a nearby coil or coils where they are measured.
EDDY CURRENTS (ELECTRICITY) - An electromagnetic nondestructive testing method in
which eddy-current flow is induced in the test object. Changes in flow caused by variations
in the object are deflected into a nearby coil or coils where they are measured.
EDDY CURRENTS (STEAM TURBINES) - Impulse Turbine - As the steam passes through
convergent nozzles, if the exit pressure is less than 0.577 x inlet pressure (the critical
pressure for nozzles), eddy-currents are developed and the exit velocity will be less than
calculated.
EDTA - A chelating agent used with boiler water treatment. Often referred as the
replacement for the phosphate-hydroxide treatment method.
EFFECTIVE TEMPERATURE - Overall effect on a human of air temperature, humidity and air
movement.
EFFLUENT - The solution which emerges from an ion-exchange column.
ELASTIC LIMITS -
ELECTRIC DEFROSTING - Use of electric resistance heating coils to melt ice and frost off
evaporators during defrosting.
ELECTRICAL CIRCUIT - A power supply, a load, and a path for current flow are the
minimum requirements for an electrical circuit.
ELECTROCHEMICAL REACTIONS - A metal wasting process, due to the fluid (boiler water)
being subjected to an electrical current.
ELECTRODE BOILER - A boiler which generates steam or hot water by the action of
immersed electrodes which conduct electricity through the boiler water, which, in turn,
generates heat by its resistance to electric current.
ELECTRODIALYSIS - This is a membrane process where an applied electric charge draws
impurity ions through permeable membranes to create high purity feedwater streams or
low purity waste streams.ELECTROLYSIS - Chemical decomposition caused by action of an electric current in a
solution.
ELECTROLYTE - A chemical compound which dissociates or ionizes in water to produce a
solution which will conduct an electric current; an acid, base, or salt.
ELECTROMECHANICAL - Converting electrical input into mechanical action. A relay is an
electromechanical switch.
ELECTRO REGENERATION - Hydrogen and hydroxyl ions are formed be electrical splitting
of water molecules and are swept through the unit by steady, low-voltage direct current,
continuously cleansing the resin beads and carrying away the unwanted salts
ELEMENT - A pure substance that cannot be broken down by chemical means to a simpler
substance.
ELEVATION HEAD - The energy possessed per unit weight of a fluid because of its
elevation.
ELUTION - The stripping of adsorbed ions from an ion-exchange material by the use of
solutions containing other ions in concentrations higher than those of the ions to be
stripped.
Emissions: The gases and airborne particles produced during Combustion.
EMULSION - A colloidal dispersion of one liquid in another.
ENDOTHERMIC REACTION - Pertaining to a chemical reaction which is accompanied by an
absorption of heat.
ENERGY - Expressed in kilowatt-hours (kWh) or watt hours (Wh), and is equal to the
product of power and time.
ENERGY - In the simplest terms, energy is the ability to perform work. It may exist in
several forms, such as heat energy, mechanical energy, chemical energy, or electrical
energy, and may be changed from one form to another.
ENERGY - The ability to do work. Energy can exist in one of several forms, such as heat,
light, mechanical, electrical or chemical. Energy can neither be created nor destroyed, but
can be transferred from one form to another. Energy can also exist in one of two states,
either potential or kinetic.
ENERGY (CONSUMPTION) CHARGE - That part of an electric bill based on kWh
consumption (expressed in cents per kWh). Energy charge covers cost of utility fuel,
general operating costs, and part of the amortization of the utility's equipment.
Energy = power x time
( 1 ) Expressed in kilowatt-hours (kWh) or watt hours (Wh), and is equal to the product of
power and time.
( 2 ) The ability to do work. Energy can exist in one of several forms, such as heat, light,
mechanical, electrical or chemical. Energy can neither be created nor destroyed, but can
be transferred from one form to another. Energy can also exist in one of two states, either
potential or kinetic.
ENGINE - Prime mover; device for transforming fuel or heat energy into mechanical
energy. ENGINE OIL - An oil used to lubricate an internal combustion engine.
ENTHALPY - The total quantity of heat energy contained in a substance, also called total
heat; the thermodynamic property of a substance defined as the sum of its internal energy
plus the quantity Pv/J, where P = pressure of the substance, v = its volume, and J = the
mechanical equivalent of heat.
ENTRAINMENT - The transport of water into a gas stream. In a boiler, this is carryover, in
a cooling tower, drift.
ENTRAINMENT (HVAC) - The capture of part of the surrounding air by the air stream
discharged from an outlet (some times called secondary air motion).
ENTROPY - The ratio of the heat added to a substance to the absolute temperature at
which it is added.
ENVIRONMENT - The aggregate of all conditions (such as contamination, temperature,
humidity, radiation, magnetic and electric fields, shock, vibration) that externally influence
the performance of a material or component.
EPSON SALT - Magnesium sulfate.
EQUALIZING HOLE (STEAM TURBINE) - A hole in the turbine disc designed to equalize
axial thrust with impulse bladed turbines.
EQUILIBRIUM REACTIONS - The interaction of ionizable compounds in which the products
obtained tend to revert to the substance from which they were formed until a balance is
reached in which both reactants and pacts are present in definite ratios.
EQUIVALENT WEIGHT - Refers to the amount of an element combining with a unit weight
of hydrogen. In terms of water treatment, a method used to calculate the concentration of
a given ion in terms of its calcium carbonate.
EROSION , ABRASIVE - Erosive wear caused by relative motion of solid particles which are
present in fluids and are moving parallel to a solid surface.
EROSION, CAVITATION - Progressive loss of original material from a solid surface due to
continuing exposure to cavitation.
EROSION, IMPINGEMENT - Loss of material from a solid surface due to liquid
impingement.
EROSION, LIQUID - Removal of films or metal by mechanical action and corrosion of
active metal.
EROSION-CORROSION - A conjoint action involving corrosion and erosion in the presence
of a moving corrosive fluid, leading to the accelerated loss of material.
ETHANE (R-170) - Refrigerant sometimes added to other refrigerants to improve oil
circulation.
EUTECTIC - An isothermal reversible reaction in which a liquid solution is converted into
two or more intimately mixed solids on cooling.
EUTECTIC POINT - Freezing temperature for eutectic solutions.
EVACUATION - The removal of gases from a system.EVAPORATION - The change of state from liquid to vapor, for example as water
evaporates to a vapor in a cooling tower.
EVAPORATIVE CONDENSER - A condenser which has water flowing over coils containing
the refrigerant gas which is thus cooled and condensed by evaporation of that water.
EVAPORATIVE CONDENSER - Device which uses open spray or spill water to cool a
condenser. Evaporation of some of the water cools the condenser water and reduces water
consumption.
EVAPORATIVE COOLING - The adiabatic exchange of heat between air and a water spray
or wetted surface. The water approaches the wet-bulb temperature of the air, which
remains constant during its traverse of the exchanger.
EVAPORATOR - The heat exchanger in which the medium being cooled, usually air or
water, gives up heat to the refrigerant through the exchanger transfer surface. The liquid
refrigerant boils into a gas in the process of the heat absorption.
EVAPORATOR FAN - Fan which increases airflow over the heat exchange surface of
evaporators.
EVAPORATOR PRESSURE REGULATOR - Automatic pressure regulating valve mounted in
suction line between evaporator outlet and compressor inlet. Its purpose is to maintain a
predetermined pressure and temperature in the evaporator.
EVAPORATOR, FLOODED - Evaporator containing liquid refrigerant at all times.
EXFlLTRATION - The flow of air outward from a space through walls, leaks, etc.
EXFOLIATION - Scaling off of a surface in flakes or layers as the result of corrosion.
EXHAUSTION - The state in which the adsorbent is no longer capable of useful ion
exchange; the depletion of the exchanger's supply of available ions. The exhaustion point
is determined arbitrarily in terms of (1) a value in parts per million of ions in the effluent
solution; and (2) the reduction inequality of the effluent water determined by conductivity
bridge which measures the resistance of the water to the flow of an electric current.
EXOTHERMIC - Chemical reaction in which heat is released.
EXPANSION JOINT - Device in piping designed to allow movement of the pipe caused by
the pipe's expansion and contraction.
EXPANSION TANK - A reservoir usually above a closed re-circulating water system that is
blanketed with a gas to permit expansion and contraction of water in the system during
temperature changes.
EXPANSION VALVE - Device in refrigerating system which reduces the pressure from the
high side to the low side and is operated by pressure.
EXPANSION VALVE, CAPILLARY TUBE - A tube of small internal diameter used as liquid
refrigerant flow control and pressure reducer between high and low sides. Also used to
transmit pressure from the sensitive bulb of some temperature controls to the operating
element.
EXPANSION VALVE, THERMOSTATIC - Control valve operated by temperature and
pressure within evaporator. It controls flow of refrigerant. Control bulb is attached to
outlet of evaporator.EXPENDABLE REFRIGERANT SYSTEM - System, which discards the refrigerant after it has
evaporated.
EXTERNAL DRIVE - Term used to indicate a compressor driven directly from the shaft or
by a belt using an external motor. Compressor and motor are serviceable separately.
EXTERNAL EQUALIZER - Tube connected to low-pressure side of a thermostatic expansion
valve diaphragm and to exit end of evaporator.
EXTERNAL TREATMENT - Refers to the treatment of water before it enters the boiler.
EXTRACTION PUMP -
EXTRACTION TURBINE – are turbines where steam is extracted at one or more points at
constant pressure. Extraction turbines may be single or double-extraction-condensing
turbines or single-or double-extraction back-pressure turbines. The extracted steam is
used for process. Do not call these bleed turbines where steam is used for heating feed
water.
Face Area: The total plane area of the portion of a grille, coil, or other items bounded by a
line tangent
Fahrenheit: A thermometric scale in which 32 (¡F) denotes freezing and 212 (¡F) the
boiling point of water under normal pressure at sea level (14.696 psi).
FAIL SAFE - In load management, returning all loads to conventional control during a
power failure. Accomplished by a relay whose contacts are normally closed.
FAILURE - A rupture, break, or disintegration of a metal or part of an HVAC system.
FALSE BRINELING - Damage to a solid bearing surface characterized by indentations not
caused by plastic deformation resulting from overload, but thought to be due to other
causes such as fretting corrosion.
FAN PERFORMANCE CURVE - Fan performance curve refers to the constant speed
performance curve. This is a graphical presentation of static or total pressure and power
input over a range of air volume flow rate at a stated inlet density and fan speed. It may
include static and mechanical efficiency curves. The range of air volume flow rate which is
covered generally ex tends from shutoff (zero air volume flow rate) to free delivery (zero
fan static pressure). The pressure curves are generally referred to as the pressure-volume
curves.
FAN TUBE AXIAL - A propeller or disc type wheel within a cylinder and including driving
mechanism supports for either belt drive or direct connection.
FAN, CENTRIFUGAL - A fan rotor or wheel within a scroll type housing and including
driving mechanism sup ports for either belt drive or direct connection.
FAN, PROPELLER - A propeller or disc type wheel within a mounting ring or plate and
including driving mechanism supports for either belt drive or direct connection.
FAN, VANE AXIAL - A disc type wheel within a cylinder, a set of air guide vanes located
either before or after the wheel and including driving mechanism supports for either belt
drive or direct connection.
FARAD - A unit of electric capacity, designated by F.FATIGUE - The phenomenon leading to fracture under repeated or fluctuating stresses
having maximum value less than the ultimate strength of the material.
FAULT - A short circuit either line to line, or line to ground.
FEED WATER - Water which is fed to a system such as a boiler or cooling tower.
FEED WATER LINE - The piping leading to a system through which the feed water flows.
FEED WATER HEATER - A device used to heat feed water with steam.
FERRIC COAGULANT - Ferric sulfate Fe2(SO4)3 act to precipitate ferric hydroxide,
coagulate at 4.0 - 11.0 pH range.
FERRIC HYDROXIDE - The complete reaction product of iron, water, and oxygen, which
forms a red precipitate in water [Fe(OH)3]
FERRIC ION - An iron atom that has a positive electric charge of +3. (Fe2+)
FERROUS - Metallic materials in which the principle component is iron.
FERROUS HYDROXIDE - The reaction product of iron and water in the absence of oxygen;
it remains soluble in the water [Fe(OH)2].
FERROUS ION - An iron atom that has a positive electric charge of + 2(Fe2+).
FILMING AMINES - Amines that form a impervious non-wettable film, which acts as a
barrier between the metal and the condensate and provide protection against carbon
dioxide and oxygen. These amines do not neutralize carbon dioxide.
FILTER - A device to remove solid material from a fluid.
FILTER-DRIER - A combination device used as a strainer and moisture remover.
FILTRATION - Is the process of passing a liquid containing suspended matter through a
suitable porous material in such a manner as to effectively remove the suspended matter
from the liquid.
FIN - An extended surface to increase the heat transfer area, as metal sheets attached to
tubes.
FIRE POINT - The temperature at which a material will continue to burn for at least 5
seconds without the benefit of an outside flame.
FIRE TUBE - A tube, in a boiler, through which the hot gases flow and transfer heat to the
water on the outside of the tube.
FIRE WALL - The back end of a boiler, opposite the burner, at which the hot gases change
direction of flow.
FIREBRICK - A refractory brick, often made from fire clay, that is able to withstand
temperature in the range of 1500 to 1600°C, and is used to line furnaces.
FIXED DISPLACEMENT PUMP - A pump in which the displacement per cycle cannot be
varied.FLASH - The portion of a superheated fluid converted to vapor when its pressure is
reduced.
FLASH CHAMBER - A separating tank placed between the expansion valve and the
evaporator to separate and bypass any gas formed in the expansion valve.
FLASH GAS - The gas resulting from the instantaneous evaporation of refrigerant in a
pressure-reducing device to cool the refrigerant to the evaporating temperature obtaining
at the reduced pressure.
FLASH POINT - The temperature at which a material to give off sufficient vapor to form a
flammable mixture.
FLASH TANK - A vessel used for separating the liquid phase from the gaseous phase
formed from a rise in temperature and/or a reduction of pressure on the flowing stream.
FLASHING - Evaporation of a liquid into a vapor.
FLEXIBLE GEAR COUPLING -
Floating Action Controllers: Essentially two position type controllers which vary the
position of the controlled devices but which are arranged to stop before reaching a
maximum or minimum position.
FLOCCULANTS - An electrolyte added to a colloidal suspension to cause the particles to
aggregate and settle out as the result of reduction in repulsion between particles.
FLOCCULATION - The process of agglomerating coagulated particles into settable flocs,
usually of a gelatinous nature.
FLOOD BACK - The condition of liquid refrigerant returning, usually from an overfed
evaporator, to the compressor through the suction line.
FLOTATION - A process of separating solids from water by developing a froth.
FLOW RATE - The volume of solution which passes through a given quantity of resin within
a given time. Flow rate is usually expressed in terms of feet per minute per cubic foot of
resin or as milliliters per minute per milliliter of resin.
FLOW, LAMINAR OR STREAMLINE - Fluid flow in which each fluid particle moves in a
smooth path substantially parallel to the paths followed by all other particles.
FLOW, TURBULENT - Fluid flow in which the fluid moves transversely as well as in the
direction of the tube or pipe axis, as opposed to streamline or viscous flow.
FLUID - The general term that includes gas, vapor or liquid
FLUID HEAD - The static pressure of fluid expressed in terms of the height of a column of
the fluid, or of some manometric fluid, which it would support.
FLUIDIZED BED - A contained mass of finely divided solid that behaves like a fluid when
brought into suspension in a moving gas.
FLY ASH - A finely divided siliceous material formed during the combustion of coal, coke,
or other solid fuels.FOAM CARRYOVER - Is the development of excessive moisture in the steam from
carryover of foam from the drum. Usually common in low pressure boilers due to high
concentration of dissolved solids.
FOAMING - Formation of steam bubbles on the surface of the boiler water due to high
surface tension of the water.
FORCE - The action on a body which tends to change its relative condition as to rest or
motion.
FORCE PUMP - A device used to inject a solution into a closed system through an opening
such as a drain valve.
FORCED CONVECTION - Movement of fluid by mechanical force such as fans or pumps.
FORCED DRAFT COOLING TOWER - Cools water by mechanically forcing air through the
tower.
FORCE-FEED OILING - Lubrication system which uses a pump to force oil to surfaces of
moving parts.
FOULING - Deposits of impurities, dirt or foreign matter that clog systems or restrict flow
and interfere with heat transfer.
FOULING FACTOR - The degree of interference with heat transfer.
FREEBOARD - The space provided above the resin bed in an ion-exchange column to allow
for expansion of the bed during backwashing.
FREEZER - A refrigerating device designed to lower the temperature below 0°C.
FREEZER BURN - Condition applied to food which has not been properly wrapped and that
has become hard, dry and discolored.
FREEZE-UP - (1) Formation of ice in the refrigerant control device which may stop the flow
of refrigerant into the evaporator. (2) Frost formation on an evaporator which may stop
the airflow through the evaporator.
FREEZING - Change of state from liquid to solid.
FREEZING POINT - The temperature at which a liquid becomes solid.
FREON - Trade name for a family of synthetic chemical refrigerants.
FRESH WATER - Water that has little or no salt dissolved in it.
FRICTION - Friction is the resistance found at the duct and piping walls. Resistance creates
a static pressure loss in systems. The primary purpose of a fan or pump is to produce a
design volume of fluid at a pressure equal to the frictional resistance of the system and
the other dynamic pressure losses of the components.
FRICTION HEAD - The pressure in psi or feet of the liquid pumped which represents
system resistance that must be overcome.
FRIGORIFIC MIXTURE - Are substances used in laboratory methods of producing a drop in
temperature. A common example is a mixture of snow and salt.FROST - Frozen condensation.
FROST BACK - Condition in which liquid refrigerant flows from evaporator into suction line;
usually indicated by sweating or frosting of the suction line.
FROST CONTROL - Semiautomatic - Control which starts defrost part of a cycle manually
and then returns system to normal operation automatically.
FROST FREE REFRIGERATOR - Refrigerated cabinet which operates with an automatic
defrost during each cycle.
FROSTING TYPE EVAPORATOR - Refrigerating system which maintains the evaporator at
frosting temperatures during all phases of cycle.
FREQUENCY - The number of vibrations, waves, or cycles of any periodic phenomenon per
second. In architectural acoustics, the interest lies in the audible frequency range of 20 to
20000 cps Hertz (cycles per second).
FUEL KNOCK - A hammer like noise produced when fuel is not burned properly in a
cylinder.
FULL LOAD CURRENT - See Running Current.
FUMES - Solid particles commonly formed by the condensation of vapors from normally
solid materials such as molten metals. Fumes may also be formed by sublimation,
distillation, calcinations, or chemical reaction wherever such processes create airborne
particles predominantly below one micron in size. Such solid particles sometimes serve as
condensation nuclei for water vapor to form smog.
FUNGUS - A lower form of plant life which does not contain chlorophyll, for example, a
mold.
FUSIBLE PLUG - Plug or fitting made with a metal of a known low melting temperature.
Used as safety device to release pressures in case of fire.
GAGE PRESSURE - Absolute pressure minus atmospheric pressure.
GALVANIC ACTION - Wasting away of two unlike metals due to electrical current passing
between them. The action is increased in the presence of moisture.
GALVANIC CELL - Electrolytic brought about by the difference in electric potential between
two dissimilar metals.
GALVANIC COUPLE - The connection of two dissimilar metals in an electrolyte that results
in current flow through the circuit.
GALVANIZING - The coating of metal with another by an electrolytic process; for example,
electrolytically zinc-coat steel is called galvanized steel.
GAS - Usually a highly superheated vapor which, within acceptable limits of accuracy,
satisfies the perfect gas laws.
GAS - Vapor phase or strata of a substance.
GAS CONSTANT - The coefficient "R" in the perfect gas equation: PV = MRT. GAS LUBRICATION - A system of lubrication in which the shape and relative motion of the
sliding surfaces cause the formation of a gas film having sufficient pressure to separate
the surfaces.
GAS REFRIGERATION CYCLE - Where the refrigerant remains in the gaseous phase
throughout.
GAS TURBINE - An engine in which gas , under pressure is formed by combustion, is
directed against a series of turbine blades. The energy in the expanding gas is converted
into rotary motion.
GAS TURBINE COMPRESSOR - a compressor designed foe the use with gas turbine
installations. This could be centrifugal or an axial compressor.
GAS VALVE - Device in a pipeline for starting, stopping or regulating flow of gas.
GAS, INERT - A gas that neither experiences nor causes chemical reaction nor undergoes a
change of state in a system or process; e.g., nitrogen or helium mixed with a volatile
refrigerant.
GASIFICATION - When a substance is converted to become a gas.
GASKET - A device, usually made of a deformable material, that is used between two
relatively static surfaces to prevent leakage.
GAUGE MANIFOLD - Chamber device constructed to hold both compound and high
pressure gauges. Valves control flow of fluids through.
GAUGE VACUUM - Instrument used to measure pressures below atmospheric pressure.
GENERAL CORROSION - Uniform overall corrosion of metal surfaces.
GENERATING TUBE - A boiler tube used for evaporation.
GENERATOR - A machine that changes that changes mechanical energy into electrical
energy.
GFI, GFCI - Ground fault (circuit) interrupter - a device that senses ground faults and
reacts by opening the circuit.
GOVERNOR SPEED DROOP -
GRAIN - A unit of weight; 0.0648 grams; 0.000143 pounds.
GRAIN BOUNDARIES - Referring to the junction of crystallites.
GRAINS OF MOISTURE - The unit of measurement of actual moisture contained in a
sample of air. (7000 grains - one pound of water).
GRAINS PER GALLON - A unit of concentration. 1 gr/gal = 17.1 mg/L.
GRAM - A unit of weight; 15.432 grains; 0.0022 pounds.
GRAM-MILLIQUIVALENTS - The equivalent weight in grams, divided by 1000.
GRAVITY - The attraction exerted by the earth’s mass on objects at its surface.GRAVITY, SPECIFIC - Density compared to density of standard material; reference usually
to water or to air.
GREASE - A lubricant composed of an oil thickened with a soap or other thickener to a
solid or semisolid consistency.
GREASE, BLOCK - A grease that is sufficiently hard to retain its shape in block or stick
form.
GREASE, SODA BASED - A grease prepared from lubricating oil and sodium soap.
GREEN LIQUOR - The liquor resulting from dissolved molten smelt from Kraft recovery
furnace in water.
GREENSAND - Naturally occurring materials, composed primarily of complex silicates,
which possess ion-exchange properties.
GROOVING - A form of deterioration of boiler plate by a combination of localized corrosion
and stress concentration.
GROUND - Zero voltage, or any point connected to the earth or "ground".
GROUND BED - Cathodic protection, an interconnected group of impressed-current anodes
that absorbs the damage caused by generated electric current
GROUND BUS - A busbar in a panel or elsewhere, deliberately connected to ground.
GROUND COIL - Heat exchanger buried in the ground. May be used either as an
evaporator or as a condenser.
GROUND CONDUCTOR - Conductor run in an electrical system, which is deliberately
connected to the ground electrode. Purpose is to provide a ground point throughout the
system. Insulation color green. Also called "green ground".
GROUND FAULT - An unintentional connection to ground.
GROUT - To force sealing material into a soil, sand or confined small space; or the sealing
material used in grouting.
HAC - Hydrogen- assist cracking.
HALIDE LEAK DETECTOR - A device used to detect vapor leaks of halogen refrigerants. It
uses acetylene as its base.
HALIDE REFRIGERANTS - Family of refrigerants containing halogen chemicals.
HALIDE TORCH - Type of torch used to safely detect halogen refrigerant leaks in system.
HALOGENS - Substance containing fluorine, chlorine, bromine and iodine.
HARD WATER - Water that contains dissolved compounds of calcium, magnesium or both.
HARDNESS - Are generally referred to the presence of calcium and magnesium content of
the water.
HARDNESS - The scale-forming and lather-inhibiting qualities which water, high in calcium
and magnesium ions, possesses.HARDNESS CONTROL - An action designed to remove hardness and at the same time to
produce an equivalent amount of suspended solids.
HARDNESS OF CALCIUM CARBONATE - The expression ascribed to the value obtained
when the hardness-forming salts are calculated in terms of equivalent quantities of
calcium carbonate; a convenient method of reducing all salts to a common basic for
comparison.
HEAD - Pressure, usually expressed in feet of water, inches of mercury or millimeters of
mercury.
Head - The measure of the pressure of water expressed in feet of height of water: 1 psi =
2.31 feet of water.
HEAD DYNAMIC OR TOTAL - In flowing fluid, the sum of the static and velocity heads at
the point of measurement.
HEAD PRESSURE - Pressure which exists in condensing side of refrigerating system.
HEAD PRESSURE CONTROL - Pressure-operated control which opens electrical circuit if
high-side pressure becomes too high.
HEAD STATIC - The static pressure of fluid expressed in terms of the height of a column of
the fluid, or of some manometric fluid, which it would support.
HEAD VELOCITY - Height of fluid equivalent to its velocity pressure in flowing fluid.
HEADER - Length of pipe or vessel to which two or more pipe lines are joined carries fluid
from a common source to various points of use.
HEADLOSS - The loss of energy as a result of friction; commonly expressed in feet.
HEAT - Form of energy which acts on substances to raise their temperature; energy
associated with random motion of molecules.
HEAT CAPACITY - The amount of heat necessary to raise the temperature of a given mass
one degree. Numerically, the mass multiplied by the specific heat.
HEAT CONDUCTOR - A material capable of readily conducting heat. The opposite of an
insulator or insulation.
HEAT ENGINE - Mechanical devices which convert heat to work, such as the steam boiler,
gas turbine, solar energy, refrigerators, steam engines, steam turbines.
HEAT EXCHANGER - Device used to transfer heat from a warm or hot surface to a cold or
cooler surface. (Evaporators and condensers are heat exchangers.)
HEAT LAG - The time it takes for heat to travel through a substance heated on one side.
HEAT LEAKAGE - Flow of heat through a substance.
HEAT OF COMPRESSION - Mechanical energy of pressure changed into energy of heat.
HEAT OF CONDENSATION - The latent heat given up by a substance as it changes from a
gas to a liquid.HEAT OF FUSION - The latent heat absorbed when a substance changes from a solid state
to a liquid state.
HEAT OF RESPIRATION - Process by which oxygen and carbohydrates are assimilated by a
substance; also when carbon dioxide and water are given off by a substance.
HEAT OF VAPORIZATION - The latent heat absorbed by a substance as it changes from a
liquid to a vapor.
HEAT PIPE - A refrigeration device with no moving parts, but containing a refrigerants.
HEAT PUMP - A device used to transfer heat from a low temperature to a high temperature
medium also a reversed cycle in which work is the input and heat is rejected to a sink at a
higher temperature than the source.
HEAT PUMP - A refrigerating system employed to transfer heat into a space or substance.
The condenser provides the heat while the evaporator is arranged to pick up heat from air,
water, etc. By shifting the flow of air or other fluid, a heat pump system may also be used
to cool the space.
HEAT SINK - Relatively cold surface capable of absorbing heat.
HEAT TRANSFER - Flow of heat by conduction, convection and radiation.
HEAT TRANSFER - Movement of heat from one body or substance to another. Heat may be
transferred by radiation, conduction, convection or a combination of these three methods.
HEAT, SENSIBLE - Heat which is associated with a change in temperature; specific heat
exchange of temperature; in contrast to a heat interchange in which a change of state
(latent heat) occurs.
Heat, Specific- The ratio of the quantity of heat required to raise the temperature of a
given mass of any substance one degree to the quantity required to raise the temperature
of an equal mass of a standard substance (usually water at 59 F) one degree.
Heat, Total (Enthalpy) - The sum of sensible heat and latent heat between an arbitrary
datum point and the temperature and state under consideration.
HEAT-EXCHANGER MATERIALS - The metals or materials of construction of a heat
exchanger.
HEAT-TRANSFER MEDIUM - The fluid, often water, which acts as the agent or medium in a
heat exchanger through which heat is exchanged from one side to the other.
HEATING COIL - Heat transfer device consisting of a coil of piping, which releases heat.
HEATING CONTROL - Device which controls temperature of a heat transfer unit which
releases heat.
HEATING SURFACE - That surface which is exposed to the heating medium for absorption
and transfer of heat to the medium.
HENRY’S LAW - An expression for calculating the solubility of a gas in a fluid based on
temperature and partial pressure.
HENRY - The unit of self-inductance or mutual inductance in the metric system. Its symbol
is H.HERMETIC - Sealed so that the object is gas tight.
HERMETIC COMPRESSOR - Compressor which has the driving motor sealed inside the
compressor housing. The motor operates in an atmosphere of the refrigerant.
HERMETIC MOTOR - Compressor drive motor sealed within same casing which contains
compressor.
HERMETIC SYSTEM - Refrigeration system which has a compressor driven by a motor
contained in compressor dome or housing.
HERTZ - A unit in the metric system used to measure frequency in cycles per second. Its
symbol is
Hz.HIC - Hydrogen-induced cracking. (Same as hydrogen embrittlement)
HIDDEN DEMAND CHARGE - Electric bill charges that are based on cents per kWh per kW
demand contain a hidden demand charge. A low load factor for a building then penalizes
the energy user through this "hidden" charge.
HIDEOUT - Is the accumulation of chemicals on surfaces, in crevices or in deposits within
the system during normal operation.
HIGH LIMIT CONTROL - A device which normally monitors the condition of the controlled
medium and interrupts system operation if the monitored condition be comes excessive,
for example a high level of fluid in a storage tank.
HIGH SIDE - Parts of the refrigerating system subjected to condenser pressure or higher;
the system from the compression side of the compressor through the condenser to the
expansion point of the evaporator. HIGH-PRESSURE CUT-OUT - Electrical control switch
operated by the high-side pressure which automatically opens electrical circuit if too high
pressure is reached.
HIGH-SIDE FLOAT - Refrigerant control mechanism which controls the level of the liquid
refrigerant in the high-pressure side of mechanism.
HIGH-VACUUM PUMP - Mechanism which can create a vacuum in the 1000 to 1 micron
range.
HOT DECK - The heating section of a multizone system. HOT GAS BYPASS - Piping system
in refrigerating unit which moves hot refrigerant gas from condenser into low-pressure
side.
HOT GAS DEFROST - Defrosting system in which hot refrigerant gas from the high side is
directed through evaporator for short period of time and at predetermined intervals in
order to remove frost from evaporator.
HOT JUNCTION - That part of thermoelectric circuit which releases heat.
HOT PROCESS - A water treatment process, when the water is heated above the room
temperature.
HOT PROCESS PHOSPHATE SOFTENING - A process whereby the calcium and magnesium
salts containing, constituting the hardness of water, are chemically precipitated and
removed with phosphate in conjunction with caustic soda.HOT WELL - A tank used to receive condensate from various sources on its passage back
to the boiler through a feedwater system.
HOT-WATER HEATING BOILER - A boiler in which no steam is generated and from which
hot water is circulated for heating purposes and then returned to the boiler.
HOT-WATER RE-CIRCULATING SYSTEM - A heating system using water as a heat-transfer
medium through a heat exchanger or boiler to terminal heating unit.
HSC - Hydrogen stress cracking.
HSCC - Hydrogen- assisted stress-corrosion cracking.
HUMIDIFIER - A device to add moisture to air.
HUMIDIFYING - Adding of moisture to the air.
HUMIDIFYING EFFECT - The latent heat of vaporization of water at the average
evaporating temperature times the weight of water evaporated per unit of time.
HUMIDISTAT - A regulatory device, actuated by changes in humidity, used for the
automatic control of relative humidity.
HUMIDITY - Dampness of air.
HUMIDITY RATIO - The ratio of the mass of the water vapor to the mass of dry air
contained in the sample.
HUMIDITY, ABSOLUTE - The weight of water vapor per unit volume.
HUMIDITY, PERCENTAGE - The ratio of the specific humidity.
HUMIDITY, RELATIVE - The ratio of the mol fraction of water vapor present in the air, to
the mol fraction of water vapor present in saturated air at the same temperature and
barometric pressure; approximately, it equals the ratio of the partial pressure or density of
the water vapor in the air, to the saturation pressure or density, respectively, of water
vapor at the same temperature.
HUNTING - A surge of engine speed to higher number of revolutions per minute, followed
by a drop to normal engines speed without manual movement of the throttle. Is often
caused by a faulty or improperly adjusted governor.
HVAC - Heating, Ventilating, and Air Conditioning.
HVAC BOILER - Boiler for heating or air conditioning (Absorption Refrigeration)
HVAC EQUIPMENT - Apparatus or equipment used in heating, ventilating, and air
conditioning.
HYDRATION - Absorption of water by a mineral that results in a change in the nature of
the mineral.
HYDRAULIC CLASSIFICATION - The rearrangement of resin particles in an ion-exchange
unit. As the backwash water flows up through the resin bed, the particles are placed in a
mobile condition wherein the larger particles settle and the smaller particles rise to the top
of the bed.HYDRAULIC COUPLING - A fluid connection between a prime mover and the machine it
drives. It uses the action of liquid moving against blades to drive the machine.
HYDRAULIC HEAD - The force exerted by a column of liquid expressed by the height of the
liquid above the point at which the pressure is measured. Although head refers to a
distance or height, it is used to express pressure, since the force of the liquid column is
directly proportional to its height. Also called head or hydrostatic head.
HYDROCARBONS - Organic compounds containing only hydrogen and carbon atoms in
various combinations.
HYDROGEN COOLED GENERATOR - High performance is provided by effective cooling and
loss reduction.
HYDROGEN CYCLE - A complete course of cation-exchange operation in which the
adsorbent is employed in the hydrogen or free acid form.
HYDROGEN DAMAGE - A type of corrosion occurring beneath a relative dense deposit. This
type of damage can only occur if hydrogen was present in the metal. Failure takes place at
thick edges in the form of fracture, rather then thinning. Hydrogen produces the corrosion
reaction, moving into underlying metal, causing decarburization and intergranular fissuring
of the structure. Damages usually result in larger pieces of metal being blown away, rather
then just bursting.
HYDROGEN INDUCED CRACKING - Caused by the introduction of hydrogen during the
welding process.
HYDROGEN ION - A portion of the molecule of water containing one atom of hydrogen
which has a positive electric charge.
HYDROGEN-ION CONCENTRATION - The degree or quantity of hydrogen ions in a water
solution.
HYDROLOGIC CYCLE - The cycle of water from evaporation through condensation to
precipitation.
HYDROLYSIS - A chemical reaction between a mineral and water that results in dissolution
of the mineral.
HYDROMETER - Floating instrument used to measure specific gravity of a liquid.
HYDRONIC SYSTEM - A re-circulating water system used for heating and/or comfort
cooling.
HYDROPHILIC - Having an affinity for water.
HYDROSTATIC PRESSURE - The pressure at any point in a liquid at rest; equal to the
depth of the liquid multiplied by its density.
Hydroxyl - The term used to describe the anionic radical (OH-) which is responsible for the
alkalinity of a solution.
HYGROMETER - Instrument used to measure degree of moisture in the atmosphere.
HYGROSCOPIC - Ability of a substance to absorb and release moisture and change
physical dimensions as its moisture content changes.ICE CREAM CABINET - Commercial refrigerator which operates at approximately -18°C;
used for storage of ice cream.
IGNITION QUALITY - The ability of a fuel to ignite when it is injected into the compressed
air charge in a diesel cylinder. It is measured by an index called the cetane number.
IMMISCIBLE - Not capable of mixing (as oil and water).
IMPEDANCE (Z) - The quantity in an AC circuit that is equivalent to resistance in a DC
circuit, inasmuch as it relates current and voltage. It is composed of resistance plus a
purely AC concept called reactance and is expressed, like resistance, in ohms.
IMPELLER - A rotating set of vanes designed to impart rotation to a mass of fluid.
IMPINGEMENT - High-velocity flow of water or gas over a metal surface, causing
premature failure by abrasion.
IMPULSE PRINCIPLE -
INDUCTANCE - The process when a second conductor is placed next to a conductor
carrying AC current (but not touching it), the ever-changing magnetic field will induce a
current in the second conductor.
INDUCTION - The capture of part of the ambient air by the jet action of the primary air
stream discharging from a controlled device.
INDUCTION HEATING - Heating by combined electrical resistance and hysteresis losses
induced by subjecting a metal to varying magnetic field surrounding a coil carrying
alternating current.
INDUCTIVE LOADS - Loads whose voltage and current are out-of-phase. True power
consumption for inductive loads is calculated by multiplying its voltage, current, and the
power factor of the load.
INDUCTOR - A fundamental element of electrical systems constructed of numerous turns
of wire around a ferromagnetic or air core.
INERT GAS - A gas that does not readily enter into or cause chemical reactions.
INFILTRATION - Air flowing inward as through a wall, crack, etc.
INFLUENT - The solution which enters an ion-exchange unit.
INHIBITOR - An additive used to retard undesirable chemical action in a product. It is
added in small quantities to gasoline’s to prevent oxidation and gum formation, to
lubricating oils to stop color change, and to corrosive environments to decrease corrosive
action.
INORGANIC MATERIAL - Are substances not derived from living things.
INRUSH CURRENT - The current that flows the instant after the switch controlling current
flow to a load is closed. Also called "locked rotor current".
INSTANTANEOUS RATE - Method for determining when load shedding should occur. Actual
energy usage is measured and compared to a present kilowatt level. If the actual kilowatt
level exceeds a designated set point, loads will be shed until the actual rate drops below
the set point. INSULATION, THERMAL - Material which is a poor conductor of heat; used to retard or
slow down flow of heat through wall or partition.
INSULATOR - A material of such low electrical conductivity that a flow of current through it
can usually be neglected. Similarly, a material of low thermal conductivity, such as that
used to insulate structures.
INTERCOOLED CYCLE - Refers to a gas turbine employing two compressors. The
compressed air from the first compressor is cooled before being discharged to second
compressor.
INTERCOOLING - Removal of heat from compressed gas between the compression stages.
INTERGRANULAR CRACKING - Cracking or fracturing that occurs between the grains or
crystal in a polycrystalline aggregate. Also called intercrystalline cracking. Contrast with
Tran granular cracking.
INTERMITTENT BLOWDOWN - The blowdown is taken from the mud drum, waterwall
headers or the lowest point of circulation.
INTER-STAGE DIFFERENTIAL - In a multistage HVAC system, the change in temperature
at the thermostat needed to turn additional heating or cooling equipment on.
ION - An atom or radical in solution carrying an integral electric charge, either positive
(cat ion) or negative (anion).
ION EXCHANGE - A reversible process by which ions are interchanged between solids and
a liquid.
ION EXCHANGE RESIN - Cross linked polymers that form salts within ions from aqueous
solutions.
IONIC STRENGTH - A measure of strength of a solution based on both the concentrations
and valences of the ions present.
IONIZATION - The process of separation of a molecule into its electrically charged atoms
or parts.
IRON - A metallic element found as an impurity in water in very small amounts. Also a
metal which is widely used in the construction of HVAC and plumbing equipment; the
major component of steel.
IRON BACTERIA - Are filamentous organisms encountered in iron-bearing water.
ISENTROPIC PROCESS - A process carried out reversibly without energy interchange as
heat. Also a processes carried out with no entropy change.
ISOBARIC PROCESS - A process carried out at constant pressure.
ISOCHORIC PROCESS OR ISOMETRIC- A process during which the specific volume remains
constant.
ISOMETRIC PROCESS - A process carried out at constant volume.
ISOTHERMAL - Changes of volume or pressure under conditions of constant temperature.ISOTHERMAL EXPANSION AND CONTRACTION - Action which takes place without a
temperature change.
ISOTHERMAL PROCESS - For a constant temperature process involving an ideal gas,
JACKING OIL PUMP - provides oil supply when the turbine is placed on barring (slow
rotation to stop the turbine from sagging or hogging)
JET COMPRESSOR - A device employing a venture tube so that a high pressure stream
flowing through the nozzle creates a lower pressure or a vacuum into which the gas to be
compressed flows. The gas is discharged from the nozzle with the expanded high-pressure
medium.
JOULE - English Scientist James Prescott Joule (1818 - 1889)
JOULE - The unit used to measure heat, work, and energy in the metric system. Its
symbol is J. It is the amount of energy required to move an object of 1 kg mass to a
height of 1 m. Also called a newton-metre.
JOULE-THOMSON EFFECT - The change in gas temperature which occurs when the gas is
expanded adiabatically from a higher pressure to a lower pressure. The effect for most
gases, except hydrogen and helium, is a cooling of the gas.
JOURNAL - That part of a shaft or axle that rotates relative to a radial bearing.
KATA THERMOMETER - Large-bulb alcohol thermometer used to measure air speed or
atmospheric conditions by means of cooling effect.
KELVIN SCALE (K) - Thermometer scale on which unit of measurement equals the Celsius
degree and according to which absolute zero is 0 degree, the equivalent of -273.16°C.
Water freezes at 273.16 K. and boils at 373.16 K. The relationship - TK = TC + 273.16
KEROSENE - a light, hydrocarbon fuel or solvent.
KILO CALORIE - This is the amount of heat (energy) necessary to raise the temperature of
1 kg of water 1°C. (Kilo calorie = kcal)
KILO CALORIE - This is the amount of heat (energy) necessary to raise the temperature of
1 kg of water 1°C. (Kilo calorie = kcal)
KILO GRAIN - A unit of weight; 1000 grains.
KILOVOLT AMPERE - Product of the voltage times the current. Different from kilowatts
because of inductive loads in an electrical system. Abbreviated: KVA kilo watts is equal to
KVA times power factor. Kilowatt: 1000 watts. Abbreviated: kW.
KILOWATT - A measure of electrical horsepower. A metric unit of power equal to
approximately 1.34 horsepower.
KILOWATT-HOUR - A measure of electrical energy consumption. 1000 watts being
consumed per hour. Abbreviated: kWh.
KINETIC ENERGY - The ability of an object to do work by virtue of its motion. (Water
moving in a pipe has kinetic energy.) The energy terms that are usually used to describe
the operation of a pump are "pressure" and "head". In classical mechanics, equal to one
half of the body’s mass times the square of its speed.KING VALVE - Liquid receiver (refrigeration only) service valve.
KIRCHOFF’S SECOND LAW - The law stating that, at each instant of time the increase of
voltage around a close loop in a network is equal to the algebraic sum of the voltage drop.
KNOCK - In a spark ignition engine, uneven burning of the fuel/air charge that causes
violent, explosive combustion and an audible metallic hammering noise. Knock results
from premature ignition of the last part of the charge to burn.
KRAFT PROCESS - A wood-pulping process in which sodium sulfate is used in the caustic
soda pulp-digestion liquor. Also called Kraft pulping or sulfate pulping.
kW DEMAND - The maximum rate of electric power usage required to operate a facility
during a period of time, usually a month or billing period. Often called "demand".
kWh CONSUMPTION - The amount of electric energy used over a period of time; the
number of kWh used per month. Often called "consumption".
KVA - Kilo Volt Amp
LABYRINTH SEAL - A labyrinth seal consists of a number of rings 1 - 2 millimeters thick
fixed to the shaft, tapered at the outer periphery to nearly knife-sharp with a clearance to
the casing of a few hundreds of a millimeter. The rings are of brass or stainless steel, the
sharp edge gives better sealing and rubs off easily without excessive heating in case of a
slightly eccentric shaft. Some labyrinth seals are very simple, others are complicated.
LAG - A delay in the effect of a changed condition at one point in the system, on some
other condition to which it is related. Also, the delay in action of the sensing element of a
control, due to the time required for the sensing element to reach equilibrium with the
property being controlled; i.e., temperature lag, flow lag, etc.
LAMINAR FLOW - A non-turbulent flow regime in which the stream filaments glide along
the pipe axially with essentially no transverse mixing.
LANGELIER SATURATION INDEX - An index (SI) based upon the pH of saturation of
calcium carbonate; used to determine the tendencies of a water supply toward corrosion
or scaling. A positive index indicates scaling tendencies; a negative one means corrosion
tendencies. (Langlier Index = pH - pHs, where pH = actual pH of water and pHs = pH at
which water having the same alkalinity and calcium content is just saturated with calcium
carbonate.
LATENT HEAT - Change of enthalpy during a change of state, usually expressed in Btu per
lb. With pure substances, latent heat is absorbed or rejected at constant pressure.
LATENT HEAT - Heat energy absorbed in process of changing form of substance (melting,
vaporization, fusion) without change in temperature or pressure.
LATENT HEAT OF CONDENSATION - Amount of heat released (lost) by a pound of a
substance to change its state from a vapor (gas) to a liquid.
LATENT HEAT OF FUSION - The heat required to change 1.0 kg of a substance from the
solid to the liquid state.
LATENT HEAT OF VAPORIZATION - The energy required to produce saturated vapor from
saturated liquid at constant pressure per unit mass of fluid.LAW OF PARTIAL PRESSURE, DALTON’S - Each constituent of a mixture of gases behaves
thermodynamically as if it alone occupied the space. The sum of the individual pressures
of the constituents equals the total pressure of the mixture.
LEADING EDGE - Refers to the point where the steam enters the blade of an impulse
turbine.
LEAK DETECTOR - Device or instrument such as a halide torch, an electronic sniffer; or
soap solution used to detect leaks.
LEAKAGE - In water treatment, it refers to the passing of impure steam or boiler water
through the drum internals.
LEAKAGE - In water treatment, the phenomenon in which some of the influent ions are not
adsorbed and appear in the effluent when a solution is passed through an under
regenerated exchange resin bed.
LIGHT CRUDE OIL - A crude oil of relatively high API gravity (usually 40°C degrees or
higher).
LIGHT EMITTING DIODE - A low current and voltage light used as an indicator on load
management equipment. Abbreviated: LED.
LIME - A common water treatment chemical.
LIME-SODA SOFTENING - A process by which the calcium and magnesium salts,
constituting the harness content of a water, are chemically precipitated and removed.
LINE VOLTAGE - In the control industry, the normal electric supply voltages, which are
usually 120 or 240 volts.
LIQUEFACTION - The change of state from a gas to a liquid. (The term liquefaction is
usually used instead of condensation when referring to substances which are in a gaseous
state at ordinary pressures and temperatures.)
LIQUID - Substance whose molecules move freely among themselves, but do not tend to
separate like those of gases.
LIQUID ABSORBENT - Chemical in liquid form which has the property to "take on" or
absorb other fluids. Glycol is such a liquid and widely use in the petroleum chemical
industry
LIQUID IMPINGEMENT - Material removal due to action of an impingement stream of a
fluid.
LIQUID INDICATOR - Device located in liquid line which provides a glass window through
which liquid flow may be watched.
LIQUID LINE - Tube which carries liquid refrigerant from the condenser or liquid receiver
to the refrigerant control mechanism.
LIQUID LINE CHARGING VALVE - The line used for charging from the high side of the
refrigeration system.
LIQUID NITROGEN - Nitrogen in liquid form which is used as a low temperature refrigerant
in expendable or chemical refrigerating systems.LIQUID PENETRANT INSPECTION - A type of nondestructive inspection that locates
discontinuities that are open to the surface of a metal by first allowing a penetrating dye
or fluorescent liquid to infiltrate the discontinuity, removing the excess penetrant, and
then applying a developing agent that causes the penetrant to seep back out of the
discontinuity and register as an indication.
LIQUID RECEIVER - Cylinder (container) connected to condenser outlet for storage of
liquid refrigerant in a system.
LIQUID RECEIVER SERVICE VALVE - Two or three-way manual valve located at the outlet
of the receiver and used for installation and service purposes. It is sometimes called the
king valve.
LIQUID-VAPOR VALVE REFRIGERANT CYLINDER - Dual hand valve on refrigerant cylinders,
which is used to release either gas or liquid refrigerant from the cylinder.
LIQUOR - Solution used in absorption refrigeration.
LITHIUM BROMIDE - A chemical used in combination with water in absorption cooling
systems.
LOAD - The amount of heat per unit time imposed on a refrigeration system or the
required rate of heat removal.
LOAD (AIR CONDITIONING) - The amount of heat per unit time imposed on a refrigeration
system or the required rate of heat removal.
LOAD TURBINE (GAS) - Is the turbine which is directly coupled to the load, which can only
be the case with a multishaft gas turbine arrangement.
LOCKED ROTOR CURRENT - See "Inrush Current".
LONGITUDINAL SEAM - A riveted or welded seam along the longitudinal axis of a boiler
shell or drum.
LOW SIDE - The refrigerating system from the expansion point to the point where the
refrigerant vapor is compressed; where the system is at or below evaporated pressure.
LOW TEMPERATURE CUTOUT, REFRIGERATON - A pressure or temperature actuated
device with sensing element in the evaporator, which will shut the system down at its
control setting to prevent freezing chilled water or to prevent coil frosting. Direct
expansion equipment may not use this device.
LOW VOLTAGE - In the control industry, a power supply of 25 volts or less.
LOW-SIDE FLOAT VALVE - Refrigerant control valve operated by level of liquid refrigerant
in low-pressure side of system.
LOW-SIDE PRESSURE - Pressure in cooling side of refrigerating cycle.
LOW-SIDE PRESSURE CONTROL - Device used to keep low side evaporating pressure from
dropping below certain pressure.
LUBRICANT - A substance - usually petroleum based, that is used to reduce friction
between two moving parts.
LUBRICANT, BONDED FILM - (see lubricant, bonded solid).LUBRICANT, BONDED SOLID - A solid lubricant dispersed in a continuous matrix of a
binder or attached to a surface by an adhesive material.
LUBRICANT, CHLORINATED - A lubricant containing a chlorine compound that reacts with
a rubbing surface at elevated temperatures to protect it from sliding damage, (see
extreme pressure lubricant).
LUBRICANT, SYNTHETIC - A lubricant produced by synthesis rather than by extraction or
refinement.
LUBRICATION, AERODYNAMIC - (see gas lubrication).
LUBRICATION, AEROSTATICS - (see pressurized gas lubrication).
LUBRICATION, BATH - (see lubrication, flood).
LUBRICATION, BOUNDARY - A condition of lubrication in which the friction and wear
between two surfaces in relative motion are determined by the properties of the surfaces
and by the properties of the lubricant other than bulk viscosity.
LUBRICATION, DRIP FEED - A system of lubrication in which the lubricant is supplied to
the bearing surface in the form of drops at regular intervals.
LUBRICATION, DRY FILM - Lubrication that involves the application of a thin film of solid
lubricant to the surface or surfaces to be lubricated.
LUBRICATION, FLOOD - A system of lubrication in which the lubricant is supplied in a
continuos stream at low pressure and subsequently drains away.
LUBRICATION, FULL FILM - A type of lubrication wherein the solid surfaces are separated
completely by an elstohydrodynamic fluid film.
LUBRICATION, MAGNETO HYDRODYNAMIC Hydrodynamic lubrication in which a significant
force contribution arises from electromagnetic interaction.
LUBRICATION, MELT - Lubrication provided by steady melting of lubricating species. Also
phase-change lubrication.
LUBRICATION, MIST - Lubrication by an oil mist produced by injecting oil into a gas
stream.
LUBRICATION, OIL FOG - (see mist lubrication).
LUBRICATION, OIL RING - A system of lubrication for horizontal shafts. A ring of larger
diameter rotates with the shaft and collects oils from a container beneath.
LUBRICATION, PAD - A system of lubrication in which the lubricant is delivered to a
bearing surface by a pad of felt or similar material.
LUBRICATION, PRESSURIZED GAS - A system of lubrication in which a gaseous lubricant is
supplied under sufficient external pressure to separate the opposing surfaces by a gas
film.
LUBRICATION, SOLID-FILM - Lubrication by application of a solid lubricant.
LUBRICATION, SPLASH - A system of lubrication in which the lubricant is splashed onto
the moving parts.LUBRICATION, THICK FILM - (also known as flood lubrication).
LUBRICATION, THIN FILM - (also known as boundary lubrication).
LUBRICATION, VAPOR-PHASE - A type of lubrication in which one or more gaseous
reactants are supplied to the vicinity of the surface to be lubricated and which
subsequently react to form a lubricious deposit on that surface.
LUBRICATION, WASTE - A system of lubrication in which the lubricant is delivered to a
bearing surface by cloth waste or yarn.
LUBRICATION, WICK - A system of lubrication in which the lubricant is delivered to a
bearing surface by means of a wick.
LUBRICITY - The ability of a lubricant to reduce wear and friction, other than by its pure
viscous properties.
MAGNESIUM - A scale forming element found in some boiler feed water.
MAGNETIC FIELD - The region within which a body or current experiences magnetic force.
MAGNETIC FLUX - The rate of flow of magnetic energy across or through a surface.
MAGNETIC IRON OXIDE (Fe3O2) - Partially oxidized iron.
MAGNETIC PARTICLE INSPECTION - A nondestructive method of inspection for
determining the extent of surface cracks and similar imperfection in ferromagnetic
materials.
MAGNETIC POLE -The area on a magnetized part at which the magnetic field leaves or
enters the part. It is the point of maximum attraction in a magnet.
MAGNETIC REFRIGERATION - Where very low temperatures are obtained by using
paramagnetic salts with magnets.
MAKEUP WATER - Water fed to a system to replace that which is lost - for example, water
fed to a boiler to replace that lost as steam or condensate; water fed to a cooling tower to
replace that lost by evaporation, drift, or other causes.
MALLEABILITY - The characteristic of metals that permits plastic deformation in
compression without fracture.
MANGANESE - A metallic element occasionally found in very small amounts as an impurity
in well-water supplies.
MANIFOLD, SERVICE - Chamber equipped with gauges and manual valves, used by service
technicians to service refrigerating systems.
MANIFOLDING - A method of circulating the refrigerant through separate rows of tubes
and mostly used with direct-expansion or dry evaporators.
MANOMETER - A device to measure small to moderate pressure differentials. Device is
general constructed from glass or plastic tubes filled with water, oil, alcohol or other
suitable fluids.MANOMETER - An instrument for measuring pressures: especially a U-tube partially filled
with a liquid, usually water, mercury, or a light oil, so constructed that the amount of
displacement of the liquid indicates the pressure being exerted on the instrument.
MANUAL FROST CONTROL - Manual control used to change operation of refrigerating
system to produce defrosting conditions.
MASS - The quantity of matter in a body as measured by the ratio of the force required to
produce a given acceleration, to the acceleration.
MASTER (CENTRAL) CONTROL - Control of all outlets from one point.
MCM - Thousand circular mill used to describe large wire sizes.
MECHANICAL CYCLE -
MECHANICAL SEALS - A mechanical device used to control leakage from the stuffing box
of a pump. Mechanical seals are usually made of two flat surfaces, one of which rotates on
a shaft. The two flat surfaces are of such tolerances as to prevent the passage of water
between them.
MECHANICAL WEAR - Removal of material due to mechanical process under conditions of
sliding, rolling, or repeated impact. Included are abrasive wear, fatigue wear and adhesive
wear, but not the corrosive and thermal wear.
MELTING POINT - For a given pressure, the temperature at which the solid and liquid
phases of the substance are in equilibrium.
MELTING POINT - Temperature at atmospheric pressure at which a substance will melt.
MEMBRANE - A barrier, usually thin, that permits the passage only of particles up to a
certain size or of special nature.
MEMBRANE - A thin sheet or layer.
MERCAPTAN - A compound chemically similar to alcohol, with sulfur replacing the oxygen
in the chemical structure. Many mercaptans have an offensive odor and are used as
deodorants in natural gas.
METALLURGICAL FACTOR - The condition of the metal, such as inclusions, chemical
segregation’s, cold work and others, which have an impact upon the rate of
electrochemical corrosion rates.
MICA - A silicate material used with high pressure gauge glasses on boilers.
MICHEL THRUST BEARING -
MICROBAR - A unit of pressure equal to 1 dyne/cm2 (one millionth of the pressure of the
atmosphere).
MICRO FILTRATION - A membrane filtration process, which forces water through a porous
barrier. Pores are usually between 0.1 to 20 m , w h e n u s e d fo r w a te r p u rifica t io n . Fo r
filtering purposes, pore sizes are .045
m.
Micron - A unit of length, the thousandth part of 1 mm of the millionth of a meter. Microprocessor - A small computer used in load management to analyze energy demand
and consumption such that loads are turned on and off according to a predetermined
program.
MILD STEEL - A low-carbon steel of ordinary production.
MILL SCALE - A natural black iron oxide coating loosely adhering to the interior of new
piping or tubes.
MINERAL - A naturally occurring inorganic substance having specified chemical
composition and crystalline structure.
MISCIBILITY - The ability of two liquids, not mutually soluble, to mix.
MIX BED DEMINERALIZER - Having a mixture of cation and anion exchange resin in the
same housing.
MIXED PRESSURE TURBINE -
MIXTURE - A physical blend of two or more substances.
MODULATING - Type of device or control which tends to adjust by increments (minute
changes) rather than by either "full on" or "full off" operation.
MODULATING CONTROL - A mode of automatic control in which the action of the final
control element is proportional to the deviation, from set point, of the controlled medium.
MODULATING REFRIGERATION CYCLE - Refrigerating system of variable capacity.
MODULUS OF ELASTICITY (E) - The measure of rigidity or stiffness of a material.
MOISTURE INDICATOR - Instrument used to measure moisture content of a refrigerant.
MOLLIER DIAGRAM - An enthalpy-entropy or enthalpy-pressure chart showing the
thermodynamic properties of a fluid.
MONOMER - A molecule, usually an organic compound, having the ability to join with a
number of identical molecules to form a polymer.
MOTOER CONTROL CENTER - A single metal enclosed assembly containing a number of
motor controllers and possibly other devices such as switches and control devices.
MUD DRUM - A pressure chamber of a drum or header type located at the lower extremity
of a water tube boiler and fitted with blowoff valve.
MULLION HEATER - Electrical heating element mounted in the mullion. Used to keep
mullion from sweating or frosting.
MULTIPLE STAGE COMPRESSOR - Compressor having two or more compressive steps.
Discharge from each step is the intake pressure of the next in series.
MULTIPLE SYSTEM - Refrigerating mechanism in which several evaporators are connected
to one condensing unit.
MULTI-SHAT GAS TURBINE - A gas turbine having more than one shaft, like the dual shaft
arrangement.MULTISTAGE COMPRESSION REFRIGERATION SYSTEM - Where the refrigerant is
vaporized and condensed alternately and is compressed in the vapor phase.
MULTISTAGE THERMOSTAT - A thermostat which controls auxiliary equipment for heating
or cooling in response to a greater demand for heating or cooling.
NAPHTA - A volatile, flammable liquid hydrocarbon distilled from petroleum and used as a
solvent or fuel.
NATURAL CIRCULATION - The circulation of a boiler caused by differences in density. Also
referred as thermal or thermally induced circulation.
NATURAL CONVECTION - Movement of a fluid caused only by temperature differences
(density changes).
NATURAL DRAFT COOLING TOWER - Cools water by moving air at low velocities.
NATURAL GAS - A highly compressible, highly expandable mixture of hydrocarbons having
a low specific gravity and occurring naturally in gaseous form. Besides hydrocarbon gases,
natural gas may contain quantities of nitrogen, helium, carbon dioxide, hydrogen sulfide
and water vapor.
NATURALLY ASPIRATED - A term used to describe a diesel engine in which air flows into
the engine by means of atmospheric pressure only.
NC - Normally closed contacts of a relay.
NEGATIVE CHARGE - The electrical potential which an atom acquires when it gains one or
more electrons; a characteristic of an anion.
NET POSITIVE SUCTION - The difference between total pressure and vapor pressure in a
fluid flow, expressed in terms of equivalent height or "head".
NEUTRAL - The circuit conductor that is normally grounded or at zero voltage difference to
the ground.
NEUTRALIZATION NUMBER - An ASTM number given to quenching oils that reflect the oil’s
tendency toward oxidation and sludging.
NEUTRALIZER - A substance that will combine with an acid or alkali chemically, thus
removing the acidity or alkalinity.
NEUTRALIZING AMINES - Are amines used to neutralize the acid generated by the
dissolution of carbon dioxide.
NEWTON - The unit of force in the metric system. A Newton is the force required to
accelerate an object of 1 kilogram mass to a velocity of 1 meter per second in 1 second.
NIPPLE - A short, threaded tubular coupling, used for making connections between pipe
joints.
NITROGEN BLANKETING - Used with wet standby, where the space above the water level
is filled with nitrogen at about 5 to 10 psig in order to keep the oxygen out.
NITROGEN DIOXIDE - Mildly poisonous gas (NO2) often found in smog or automobile
exhaustNO - Normally open contacts of a relay.
NOBEL METAL - A chemically inactive metal, such as gold.
NO-FROST FREEZER - Low-temperature refrigerator cabinet in which no frost or ice
collects on freezer surfaces or materials stored in cabinet.
NOISE - Any undesired sounds, usually of different frequencies, resulting in an
objectionable or irritating sensation.
NOMINAL SIZE - A designated size that may be different from the actual size.
NOMINAL SIZE TUBING - Tubing measurement which has an inside diameter the same as
iron pipe of the same stated size.
NON-CARBONATED HARDNESS - Hardness in water caused by chlorides, sulfates, and
nitrates of calcium and magnesium.
NON-CODE INSTALLATION - Functional refrigerating system installed where there are no
local, state, or national refrigeration codes in force.
NON-CONDENSABLES - Gaseous material not liquefied when associated water vapor is
condensed in the same environment.
NON-DESTRUCTIVE INSPECTION (NDI) - A procedure such as ultrasonic or radiographic
inspection, for determining the quality of a material without permanently altering
anything.
NON-FERROUS ALLOY - Alloy containing less then 50 % iron.
NON-FROSTING EVAPORATOR - Evaporator which never collects frost or ice on its surface.
Uses only thermostatic expansion valves.
NON-MECHANICAL REFRIGERATION - Those that obtain the required high and low
pressure by some method other than a mechanical compressor.
NON-REACTIVE SILICA - Is a polymeric form of silica; thermally unstable which reverts to
normal silica when heated. Difficult to detect, but may be present when boiler feedwater
shows none, but boiler water reads silica.
NORMAL CARRYOVER - Refers to the carryover which occurs in any boiler operating under
the best conditions.
NORMAL CHARGE - Thermal element charge which is part liquid and part gas under all
operating conditions.
NORMALLY OPEN - (OR NORMAL CLOSED) The position of a valve, damper, relay contacts,
or switch when external power or pressure is not being applied to the device. Valves and
dampers usually are returned to a "normal" position by a spring.
NOZZLE GOVERNING -
NTU - Nephelometric turbidity unit. A light -interference analytical method to measure the
turbidity of water.NUCLEATE BOILING - The even boiling of water in which steam bubbles are formed within
the boiler water gradually and are evenly distributed rather than being suddenly formed
and erratically distributed
OCCLUSION - An absorption process by which one solid material adheres strongly to
another, sometimes occurring by co precipitation.
OCTANE RATING - A classification of gasoline according to its antiknock qualities. The
higher the octane number or rating, the greater are the antiknock qualities of the gasoline.
OCTYL ALCOHOL - ETHYL HEXANOL - Additive in absorption machines to reduce surface
tension in the absorber.
OFFSET - Term used to describe the difference between the set point and the actual
operating or control point.
OHM - The unit of electrical resistance equal to the resistance through which a current of 1
ampere will flow when there is potential difference of one volt across it.
OHM’S LAW - The relationship between current and voltage in a circuit. It states that
current is proportional to voltage and inversely proportional to resistance. Expressed
algebraically, in DC circuits I=E/R; in AC circuits I=E/R.
OIL - A liquid of vegetable, animal, mineral, or synthetic origin that feels slippery to the
touch.
OIL BINDING - Condition in which an oil layer on top of refrigerant liquid may prevent if
from evaporating at its normal pressure temperature.
OIL GROOVE - A channel or channels in a bearing to improve oil flow through the bearing.
OIL RING LUBRICATION - A system of lubrication for horizontal shafts. A ring of larger
diameter rotates with the shaft and collects oils from a container below.
OIL SEPARATOR - Device used to remove oil from gaseous refrigerant or steam.
OIL, MINERAL - A refined hydrocarbon oil without animal or vegetable additives.
OIL, MULTI-GRADE - An oil having relative little change in viscosity over a specified
temperature range.
OIL, NEUTRAL - A lubricating oil obtained by distillation, not treated with acid or with
alkali.
OIL, TURBINE - An oil used to lubricate bearings in a steam or gas turbine.
ONCE-THROUGH BOILER - A steam generating unit usually operated above the critical
pressure in which there is no re-circulation of the working fluid in any part of the unit.
ON-OFF CONTROL - A two position action which allows operation at either maximum or
minimum condition, or on or off, depending on the position of the controller.
OPEN CIRCUIT - The absence of a direct connection between two points in an electrical
network.
OPEN CYCLE - A gas turbine arrangement, in were the exhaust gases from the turbine are
exhausted to the atmosphere without any further treatment.OPEN RE-CIRCULATING WATER SYSTEM - A system, using continuously circulated water
as a heat-transfer medium, in which the water is exposed at one point to the atmosphere
for either discharge or absorption of heat.
OPERATING POINT - The value of the controlled condition at which the controller actually
operates. Also called control point.
OPERATING PRESSURE - Actual pressure at which the system works under normal
conditions. This pressure may be positive or negative (vacuum).
ORGANIC GROWTH - A substance resulting from the growth of biological organisms such
as fungi, algae, and slime bacteria.
ORGANIC MATERIAL - Contain carbon and usually hydrogen and are derived from living
things.
ORGANIC OXYGEN SCAVENGERS - These are organic compounds such as hydroquinone
and ascorbate to remove dissolved oxygen from the boiler feedwater and condensate.
ORIFICE - Accurate size opening for controlling fluid flow.
ORSAT ANALYZER - A furnace atmosphere analysis device in which gases are absorbed
selectively (volumetric basis) by passing them through a series of pre-selected solvents.
OSHA - Occupational Safety and Health Administration.
OSMOSIS - The passage of water through permeable membrane separating two solutions
of different concentration; the water passes into the more concentrated solution.
OUTSIDE AIR OPENING (HVAC) - Any opening used as an entry for air from outdoors.
OVER CURRENT DEVICE - A device such as a fuse or a circuit breaker designed to protect
a circuit against excessive current by opening the circuit.
OVERFLOW PIPE - A pipe installed at a top of a tank to enable the liquid within to be
discharged to another vessel when the tank is filled to capacity.
OVERLOAD - A condition of excess current; more cur rent flowing than the circuit was
designed to carry.
OVERRIDE - A manual or automatic action taken to by pass the normal operation of a
device or system
OVERSPEED TRIP - On steam turbines, a mechanism that provides absolute reliable
overspeed protection by shutting off the steam supply.
OXIDATION - The reaction of an element or substance with oxygen, e.g., iron is oxidized
by reaction with oxygen to form rust (iron oxide).
OXIDIZING AGENT - Any substance such as oxygen, or chlorine, that will readily add (take
on) electrons.
OXIDIZING ATMOSPHERE - A furnace atmosphere with an oversupply of oxygen that tends
to oxidize materials placed in it.
OXIDIZING BIOCIDE - An agent, such as chlorine, which will kill bacteria by the chemical
process of oxidation.OXYACETYLENE WELDING - An oxyfuel gas welding process in which the fuel gas is
acetylene.
OXYGEN CONCENTRATION CELL - (see differential aeration cell).
OXYGEN CONCENTRATION CELL - The surface area in contact with the media of higher
oxygen concentration becomes the cathodic area, and the area with the lower oxygen
concentration becomes the anode.
OXYGEN PITTING - Damage caused due to the presence of oxygen in the feedwater.
Damage results are small pit-like holes in the metal.
OXYGEN SCAVENGER - A substance that will absorb oxygen by chemical reaction.
OZONE - Triatomic oxygen (03). Sometimes used in cold storage or air conditioning
installations as an odor eliminator. Can be toxic in certain concentrations.
PACKAGE UNITS, (REFRIGERATION) - Complete refrigerating system including
compressor, condenser and evaporator located in the refrigerated space.
PACKED COLUMN - A tower filled with small objects, designed to obtain large surfaces per
volume between rising vapors and a descending liquid.
PACKING - Material made usually of woven animal, plant, mineral or metal fiber and some
type of lubricant, placed in rings around the shaft of a pump and used to control leakage
from the stuffing box.
PACKING - The fill in a confined space in a stripping vessel, ranging from simple shaped
units such as rocks or slats to complex shapes that provide large surface area per unit
volume.
PACKING GLAND - The metal part that compresses and holds packing in place in a stuffing
box.
PARALLEL CIRCUIT - One where all the elements are connected across the voltage source.
Therefore, the voltage on each element is the same but the current through each may be
different.
PARSON TURBINE -
PARTIAL PRESSURES - Condition where two or more gases occupy a space and each one
creates part of the total pressure.
PASCAL - The accepted metric unit of measurement or pressure and stress component in
the measurement of viscosity. A Pascal is equal to a force of 1 Newton acting an area of 1
square meter. The symbol is Pa.
PASCAL'S LAW - Pressure imposed upon a fluid is transmitted equally in all directions.
PASSIVATING (ANODIC) INHIBITORS - A material capable of forming a protective oxide
film on metal surfaces.
PASSIVATION - The process of rendering a metal surface chemically inactive, either by
electrochemical polarization or by contact with a passivating agent.
PASSIVATOR - A type of corrosion inhibitor that appreciably changes the potential of a
metal to a more noble (positive) value.PASSIVATOR - A type of corrosion inhibitor that appreciably changes the potential of a
metal to a more positive value.
PASSIVE-ACTIVE CELL - A corrosion cell in which the anode is a metal in that active state
and the cathode is the same metal in the passive state.
PASSIVITY - A condition on metal surfaces that inhibits electrochemical action between the
metal and its environment, such as with boiler water.
PATHOGENIC BACTERIA - Disease-causing bacteria.
PEAK DEMAND - The greatest amount of kilowatts needed during a demand interval.
PEAK LOAD PRICING - A pricing principle that charges more for purchases that contribute
to the peak demand and, thereby, cause the expansion of productive capacity when the
peak demand exceeds the peak capacity (less minimum excess capacity). In the electric
power industry, this means charging more hr electricity bought on or near the seasonal
peak of the utility or on or near the daily peak of the utility. The latter requires special
meters; the former does not.
PEAKING LOAD - Is the electrical load drawn on the system during high power usage.
Usually on very hot or cold days or during the supper hour.
PELTIER EFFECT - When direct current is passed through two adjacent metals one junction
will become cooler and the other will become warmer. This principle is the basis of
thermoelectric refrigeration.
PERFECT GAS - A hypothetical gas obeying the relation pv = RT.
PERMANENT GASES - Cryogenic refrigerants.
PERMEABILITY - The ability of a body to pass fluid under pressure.
PETROGRAPHIC STUDY OF BOILER SCALES The systematic and descriptive study of rocks.
This method also allows the identification of boiler scales, since scale can consist of a large
variety of minerals
PETROLEUM OIL - (see mineral oils).
pH - The negative logarithm of the hydrogen-ion concentration of a solution; simply a
measure of the relative acidity or alkalinity of a water solution. (pH 1 very acidic; pH 14,
very basic; pH 7, neutral).
pH OF SATURATION (pHs) - The pH at which a sample of water is saturated with a specific
salt; for example, the pH of saturation of calcium carbonate is the pH of a saturated
solution of calcium carbonate.
PHASE - Part of an AC voltage cycle. Residential electrical service is 2-phase; commercial
facilities are usually 3-phase AC voltage.
PHIAL -Term sometimes used to denote the sensing element on a thermostatic expansion
valve.
PHOSPHATE - An ion, compound, or
salt containing phosphorus and oxygen, such as
sodium phosphate (Na3P04).PHOSPHATE TREATMENT - An internal boiler water treatment method to reduce calcium in
the boiler with low hardness feedwater.
PHYSICAL STABILITY - The quality which an ion-exchange resin must possess to resist
changes that might be caused by attrition, high temperatures, and other physical
conditions.
PHYSICAL WATER TREATMENT - Refers to the treatment of removing dissolved gases from
the boiler feedwater, using steam.
PIG IRON - High-carbon iron made by reduction of iron ore in the blast furnace.
PILOT DUTY RELAY - A relay used for switching loads such as another relay or solenoid
valve coils. The pilot duty relay contacts are located in a second control circuit. Pilot duty
relays are rated in volt-amperes (VA).
PILOT OIL PRESSURE -
PIPE SCALE - Rust or mill scale found on the interior of water pipe.
PIT - Corrosion localized in a small spot.
PITOTE TUBE - An open ended tube arrangement to face against the current of a stream of
fluid; used in measuring the velocity head of a flowing medium.
PITS - Petroleum Industry Training Service. (Canada)
PITTING - Localized corrosion of a metal characterized by small blisters under which holes
have perforated the metal.
PLASTIC DEFORMATION -
PLASTICITY - The ability of a substance to be deformed without rupturing.
PLENUM CHAMBeR - An air compartment connected to one or more distributing ducts.
PLENUM CHAMBER - Chamber or container for moving air or other gas under a slight
positive pressure.
PNEUMATIC - Operated by air pressure.
PNEUMATIC-ELECTRIC (PE) SWITCHES - Device that operates an electric switch from a
change of air pressure.
pOH - An expression of the alkalinity of a solution; the negative logarithm of the hydroxyl
ion concentration.
POINT, CRITICAL - Of a substance, state point at which liquid and vapor have identical
properties; critical temperature, critical pressure, and critical volume are the terms given
to the temperature, pressure, and volume at the critical point. Above the critical
temperature or
POLARITY - The direction of current flow in a DC circuit. By convention, current flows from
plus to minus. Electron flow is actually in the opposite direction.
POLARIZE - In corrosion, to develop a barrier on the anodic or cathodic surface, disrupting
the corrosion process.POLE - An electrical connection point. In a panel, the point of connection. On a device, the
terminal that connects to the power.
POLYELECTROLYTE - A water-soluble polymer that is highly charged with cationic or
anionic sites. Used as an aid with coagulants.
POLYMER - A chemical compound formed by the adjoining of many molecules of the same
characteristics; for example, polyvinyl chloride is a polymer of the molecule vinyl chloride.
POLYMERIC DISPERSANT - A water-soluble polymer that acts as a suspending agent; that
is, it promotes suspension of particles in water so that they resist settling.
POLYPHOSPHATE - A chemical compound formed by the adjoining of phosphate ions,
hence a polymer of phosphate.
POLYTROPHIC PROCESS - A non-adiabatic reversible process characterized by the
equation of path, pv = constant.
POROUS VASE - A vase having a porous construction, which was used to cool its content.
POSITIVE CHARGE - The electrical potential acquired by an atom which has lost one or
more electrons; a characteristic of a cation.
POTENTIAL ENERGY - The energy, that a body has by virtue of its position or state,
enabling it to do work. (Water in a reservoir has potential energy by virtue of its elevation
above some other point.)
POTENTIAL TRANSFORMER - A voltage transformer. The voltage supplied to a primary coil
induces a voltage in a secondary coil according, to the ratio of the wire windings in each of
the coils.
POTENTIOMETER - An electromechanical device having a terminal connected to each and
to the resistive element, and a third terminal connected to the wiper contact. The electrical
input is divided as the contact moves over the element, thus making it possible to
mechanically change the resistance.
POUR POINT - The lowest temperature at which a lubricant can be observed to flow under
specified conditions. For oil, the pour point is a temperature -15°C above the temperature
at which the oil is solid.
POUR-POINT DEPRESSANT - An additive that lowers the pour point of a lubricant.
POWER (P) - Expressed in watts (W) or kilowatts (kW), and is equal to:
POWER ELEMENT - Sensitive element of a temperature-operated control.
POWER FACTOR (pf) - A quantity that relates the volt amperes of an AC circuit to the
wattage (power = volt-amperes x power factor). Power factor also is the ratio of the circuit
resistance (R) to the impedance (Z) expressed as a decimal between zero and one (pf =
R/Z). When the power factor equals one, all consumed power produces useful work.
POWER FACTOR CHARGE - A utility charge for "poor" power factor. It is more expensive to
provide power to a facility with a poor power factor (usually less than 0.8).
POWER FACTOR CORRECTION - Installing capacitors on the utility service’s supply line to
improve the power factor of the building.ppb - equals 0.001 ppm. (Parts per billion)
PRECIPITATE - An insoluble reaction product; in an aqueous chemical reaction, usually a
crystalline compound that grows in size to become settable.
PRECIPITATING (CATHODIC) INHIBITORS - The are chemicals which form insoluble
precipitates that are able to coat and protect surfaces. They are less durable then the
passivating type inhibitors.
PRECIPITATION - A process whereby salts drop or come out of a water solution.
PRECISION PHOSPHATE TREATMENT - A phosphate treatment based upon maintaining 2
to 4 ppm of phosphate and 15 to 50 ppm of hydrate alkalinity in the boiler.
PREDICTING METHOD - A method for determining when load shedding should occur. A
formula is used to arrive at a preset kilowatt limit. Then the actual amount of energy
accumulated during the utility's demand intervals is measured. A projection is made of the
actual rate of energy usage during the rest of the interval. If the predicted value exceeds
the preset limit, loads will be shed.
PREIGNITION - A condition in an internal combustion engine characterized by a knocking
sound and caused by the fuel-air mixture having been ignited to soon because of an
abnormal condition.
PRESSURE - The normal force exerted by a homogeneous liquid or gas, per unit of area,
on the wall of its container.
PRESSURE COMPOUNDING -
PRESSURE DROP - Pressure loss in fluid pressure, as from one end of a duct or pipe to the
other, due to friction, dynamic losses, and changes in velocity pressure.
PRESSURE GAUGE - Instrument for measuring the pressure exerted by the contents on its
container.
PRESSURE HEAD - The height to which liquid can be raised by a given pressure
(sometimes referred to as pump head).
PRESSURE MOTOR CONTROL - Device which opens and closes an electrical circuit as
pressures change.
PRESSURE OPERATED THERMOMETER - Temperature indicator which is controlled by
bellows, a capillary or remote sensitive bulb.
PRESSURE REGULATOR, SUCTION (REFRIGERATION COMPRESSORS) - An automatic valve
designed to limit the suction pressure to prevent motor overload.
PRESSURE SWITCH - Switch operated by a rise or drop in pressure.
PRESSURE VELOCITY - In moving fluid, the pressure capable of causing an equivalent
velocity, if applied to move the same fluid through an orifice such that all pressure energy
expended is converted into kinetic energy.
PRESSURE, ABSOLUTE - Pressure referred to that of a perfect vacuum. It is the sum of
gauge pressure and atmospheric pressure. PRESSURE, ATMOSPHERIC - It is the pressure indicated by a barometer. Standard
atmosphere is the pressure equivalent
PRESSURE, CRITICAL - Vapor pressure corresponding to the substance's critical state at
which the liquid and vapor have identical properties.
PRESSURE, GAGE - Gauge: Pressure above atmospheric.
PRESSURE, HYDROSTATIC - The normal force per unit area that would be exerted by a
moving fluid on an infinitesimally small body immersed in it if the body were carried along
with the fluid.
PRESSURE, OPERATING - Pressure at which a system is operating.
PRESSURE, PARTIAL - Portion of total gas pressure of a mixture attributable to one
component.
PRESSURE, SATURATION- The saturation pressure for a pure substance for any given
temperature is that pressure at which vapor and liquid, or vapor and solid, can coexist in
stable equilibrium.
PRESSURE, STATIC - The normal force per unit area that would be exerted by a moving
fluid on a small body immersed in it if the body were carried along with the fluid.
Practically, it is the normal force per unit are at a small hole in a wall of the duct through
which the fluid flows (piezometer) or on the surface of a stationary tube at a point where
the disturbances, created by inserting the tube, cancel. It is supposed that the
thermodynamic properties of a moving fluid depend on static pressure in exactly the same
manner as those of the same fluid at rest depend upon its uniform hydrostatic pressure
PRESSURE, TOTAL - In the theory of the flow of fluids, the sum of the static pressure and
the velocity pressure at the point of measurement. Also called dynamic pressure.
PRESSURE, VAPOR - The partial pressure exerted by the water vapor contained in air.
PRESSURE-HEAT DIAGRAM - Graph of refrigerant pressure, heat and temperature
properties. (Mollier's diagram.)
PRESSURESTAT - A control which reacts to pressure changes in the evaporator.
PRESSURE-VELOCITY COMPOUNDING -
PRETREATMENT - Also referred to as external treatment, consisting of treating the raw
make-up water, and include removing dissolved oxygen, carbon dioxide, suspended solids,
hardness, alkalinity, silica, dissolved solids, etc..
PRIMARY AIR - The initial air stream discharged by an air outlet (the air being supplied by
a fan or supply duct) prior to any entrainment of the ambient air or for he purpose of
combustion.
PRIMARY CONSTITUENTS - Refers to the category of dissolved solids present in water at a
level of more then 5 mg/L.
PRIMARY CONTROL - A device which directly or indirectly controls the control agent in
response to needs indicated by the controller. Typically a motor, valve, relay, etc. PRIMARY ELEMENT - The portion of the controller which first uses energy derived from the
controlled medium to produce a condition representing the value of the controlled
variable; for example, a thermostat bimetal.
PRIMARY SYSTEM - A closed water system in which the water is circulated directly through
a chiller for cooling or heat exchanger or boiler for heating.
PRIME MOVER - An engine or other device by which natural source of energy is converted
into mechanical energy.
PRIMING - The phenomenon in which the level of water in a boiler is changed by bouncing
rapidly. The result is, that boiler water will enter the steam flow.
PROCESS HOT WATER - Hot water needed for manufacturing processes over and above
the "domestic hot water" that is for the personal use of industrial workers.
PROPANE - A paraffin hydrocarbon (C3H8) that is a gas at ordinary atmospheric conditions
but easily liquefied under pressure.
PROPORTIONAL BAND - The range of values of a proportional positioning controller
through which the controlled variable must pass to move the final control element through
its full operating range. Commonly used equivalents are "throttling range" and
"modulating range".
PSI - Symbol or initials used to indicate pressure measured in pounds per square inch.
PSIA - Symbol or initials used to indicate pressure measured in pounds per square inch
absolute. Absolute pressure equals gauge pressure plus atmospheric pressure. The "A"
indicates that the gauge pressure is reading in absolute.
PSIG - Symbol or initials used to indicate pressure in pounds per square inch gauge. The
"G" indicates that is gauge pressure and not absolute pressure.
PSYCHROMETER - An instrument for ascertaining the humidity or hygrometric state of the
atmosphere.
PSYCHROMETER OR WET BULB HYGROMETER – An instrument for measuring the relative
humidity of atmospheric air.
PSYCHROMETRIC CHART – A chart that shows relationship between the temperature,
pressure and moisture content of the air.
PSYCHROMETRIC MEASUREMENT - Measurement of temperature pressure and humidity
using a psychometric chart.
PSYCHROMETRY - The study of air-vapor mixtures.
PULL DOWN - An expression indicating action of removing refrigerant from all or part of a
refrigeration system.
PULSATION DAMPENER - Any gas or liquid charged, chambered device that minimizes
periodic increases and decreases in pressure.
PULSE-ECHO TECHNIQUES - Corrosion detecting processes which, by recording the action
of ultrasonic waves artificially introduced into production structures, can determine metal
thickness and detect flaws.PUMP - A device that increases the pressure on a fluid or raises it to a higher level.
PUMP DOWN - The act of using a compressor or a pump to reduce the pressure in a
container or a system.
PUMP, POSITIVE DISPLACEMENT - A pump that moves a measured quantity of fluid with
each stroke of a piston or each revolution of vanes or gears.
PUMP, ROTARY - A pump that moves fluid by positive displacement, using a system of
rotating vanes, gears, or lobes.
PUMP-DISCHARGE PRESSURE - The point of highest pressure in a re-circulating water
system which is at the discharge side of the re-circulating pump.
PURGING - Releasing compressed gas to atmosphere through some part or parts for the
purpose of removing contaminants from that part or parts.
PURGING VALVES - Devices used to remove non-condensable gases from the refrigeration
system.
PYROMETER - A device for measuring temperatures above the range of liquid
thermometers.
QUALITY - Weight fraction of the vapor in a vapor-liquid mixture.
QUICKLIME - Unslaked lime (calcium oxide).
RACEWAY - Any support system, open or closed, for carrying electric wires.
RADIAL THRUST -
RADIANT HEATING - Heating system in which warm or hot surfaces are used to radiate
heat into the space to be conditioned.
RADIATION - Transfer of heat by electromagnetic waves.
RADIATION LOSSES (STEAM TURBINE) -
RAM AIR - Air forced through the condenser due to the rapid movement of steam from the
turbine exit.
RANKINE SCALE - Name given the absolute (Fahrenheit) scale. Zero (0) R on this scale is -
460°F.
RANKINE TEMPERATURE - Degrees Fahrenheit plus 491.60.
RAPTURE MEMBRANE - A metal membrane (pressure relief device) designed to rapture at
a predetermined pressure.
RAW MAKEUP WATER - Untreated water fed to a system to replace that lost.
RAW WATER - With water treatment it means untreated feedwater or water in its natural
state, prior to any treatment.
REACTION PRINCIPLE -REAGENT - A substance, chemical, or solution used in laboratory to detect, measure, or
react with other substances, chemicals or solutions.
RE-CARBONATION - A process using carbon dioxide gas to stabilize and thereby prevent
precipitation of calcium carbonate from cold process lime or lime-soda softened water.
RECEIVER - An auxiliary storage receptacle for fluids.
RECEIVER DEHYDRATOR - Small tank which serves as liquid refrigerants reservoir and
which also contains a desiccant so remove moisture. Used on most automobile air
conditioning installations.
RECEIVER HEATING ELEMENT - Electrical resistance mounted in or around liquid receiver.
It is used to maintain head pressures when ambient temperature is low.
RECEIVER-DRIER - Cylinder (container) in a refrigerating system for storing liquid
refrigerant and which also holds a quantity of desiccant.
RECIPROCAL - A format defined by 1 divided by the complex number.
RECIPROCATING COMPRESSOR - Compressor which uses a piston and cylinder mechanism
to provide pumping action.
RECORDING THERMOMETER - Temperature measuring instrument which has a pen
marking a moving chart.
RECTIFIER - A device used to convert AC current into DC current.
RECUPERATOR - Equipment for transferring heat from gaseous products of combustion to
incoming air or fuel. The incoming material passes through pipes surrounded by a
chamber through which the outgoing gases pass.
RED WATER - Water that has a red, cloudy appearance caused by suspended red iron
oxide.
REDOX POTENTIAL - A process designed to determine if a corrosion process will occur.
REDUCING ELBOW - A fitting that makes an angle between two joints of pipe and that
decreases in diameter from one end to the other.
REDUCING FLANGE - A flange fitting used to join pipes of different diameters.
REDUCING NIPPLE - A pipe fitting that is threaded on both ends and decreases in diameter
from one end to the other.
REDUCING TEE - A "T"shaped pipe fitting with openings of two different sizes. The
relationship:
REDUCTION - Reduction is the addition of hydrogen, removal of oxygen, or the addition of
electrons to an element or compound.
REED VALVE - Thin, flat, tempered steel plate fastened at one end.
REFRIGERANT - The fluid used for heat transfer in a refrigerating system, which absorbs
heat at a low temperature and a low pressure of the fluid and rejects heat at a higher
temperature and a higher pressure of the fluid, usually involving changes of state of the
fluid. REFRIGERANT - The working fluid used in refrigerators.
REFRIGERANT CHARGE - Quantity of refrigerant in a system.
REFRIGERANT CONTROL - Device which meters flow of refrigerant between two areas of a
refrigerating system. It also maintains pressure difference between high-pressure and low
pressure side of the mechanical refrigerating system while unit is running.
REFRIGERATING CAPACITY - The ability of a system to remove heat as compared with the
cooling effect produced by melting of ice.
REFRIGERATING EFFECT - The amount of heat transferred by one kg of refrigerant as it
circulates in the refrigeration system.
REFRIGERATION - Controlled transfer of heat from a lower temperature to a higher
temperature region.
REFRIGERATION OIL - Specially prepared oil used in refrigerator mechanism which
circulates, to some extent, with refrigerant.
REFRIGERATOR - A device to transfer heat from a low temperature to a high temperature
medium.
REGENERATE - The solution used to restore the activity of an ion exchanger. Acids are
employed to restore a cat ion exchanger to its hydrogen form; brine solutions may be
used to convert the cat ion exchange to the sodium form. The anion exchanger may be
rejuvenated by treatment with an alkaline solution.
REGENERATION - Restoration of the activity of an ion exchanger by replacing the ions
adsorbed from the treated solution by ions that were adsorbed initially on the resin.
REGENERATIVE CYCLE - Is a gas turbine cycle employing a heat exchanger to recover
some of the heat before discharging the gases from the gas turbine to the atmosphere, to
recover some of the from
REGENERATIVE GAS TURBINE - Referring to a gas turbine employing heat exchanger
between the compressor and the combustor for the purpose of recovering heat.
REGENERATOR -
Register: A grille equipped with an integral damper or control valve.
REJUVENATION - (see regeneration)
RELATIVE HUMIDITY - The amount of moisture the air holds relative to the maximum
moisture the air can hold at the same temperature.
Relative Humidity (RH): The ratio of water vapor in the air as compared to the maximum
amount of water vapor that may be contained.
RELATIVE HUMIDITY -The ratio, expressed as a percentage, of the amount of water vapor
present in a given volume of air at a given temperature to the amount required to saturate
the air at that temperature.
RELAY - An electromechanical switch that opens or closes contacts in response to some
controlled action. Relay contacts can be normally open (NO) and/ or normally closed (NC).
Relays may be electric, pneumatic, or a combination of both.RELAY, THERMAL - A switching relay in which a small heater warms a bimetal element
which bends to provide the switching force.
RELIEF VALVE - Safety device on a sealed system. It opens to release fluids before
dangerous pressure is reached. Also called pressure relief valve.
REMOTE SYSTEM - Refrigerating system in which condensing unit is away from space to be
cooled.
Remote Temperature Set Point: Ability to set a temperature control point for a space from
outside the space. Often used in public areas.
RESET - A process of automatically adjusting the control point of a given controller to
compensate for changes in outdoor temperature. The hot deck control point is normally
reset upward as the outdoor temperature drops. The cold deck control point is normally
reset downward as the outdoor temperature increases.
RESET RATIO - The ratio of change in outdoor temperature to the change in control point
temperature. For example, a 2:1 reset ratio means that the control point will increase 1
degree for every 2 degrees change in outdoor temperature.
RESIDUAL - Means small amount of, like oxygen, sulfite, acid., etc..
RESISTANCE - The opposition which limits the amount of current that can be produced by
an applied voltage in an electrical circuit, measured in ohms.
RESISTANCE, THERMAL - The reciprocal of thermal conductance.
RESISTIVE LOADS - Electrical loads whose power factor is one. Usually contain heating
elements.
RESONANT VIBRATION - Everything has a natural frequency. This frequency is effected by
two properties: Mass and Stiffness. This "natural frequency" is the cause of many vibration
problems in HVAC equipment. If you strike an object (say a tuning fork or a bell) it will
continue to vibrate at its natural frequency until damping extinguishes the vibration.
RESTRICTOR - A device for producing a deliberate pressure drop or resistance in a line by
reducing the cross-sectional flow area.
Return Air: Air returned from conditioned or refrigerated space.
RETURN-STEAM CONDENSATE - That steam produced by a boiler which returns to the
boiler after it has condensed.
REVERSE CYCLE DEFROST - Method of heating evaporator for defrosting. Valves move hot
gas from compressor into evaporator.
REVERSE CYCLE REFRIGERATION - A refrigeration system which uses reject heat to
produce warmth.
REVERSE DEIONIZATION - The use of an anion-exchange unit and a cation-exchange unit
in that order-to remove all ions from solution.
REVERSE OSMOSIS - A process that reverses (by the application of pressure) the flow of
water in the natural process of osmosis so that it passes from the more concentrated to
the more dilute solution.REVERSIBLE PROCESS - A process by which a fluid is made to undergo a change of state
and by traversing the path in exactly the reverse of the original path is returned to its
original state, and all associated systems are similarly returned to their original state.
REVERSING VALVE - Device used to reverse direction of the refrigerant flow depending
upon whether heating or cooling is desired.
RING LUBRICATED SLEEVE BEARING -
RINSE - The operation which follows regeneration; a flushing out of excess regenerate
solution.
ROTARY COMPRESSOR - Mechanism which pumps fluid by using rotating motion.
RUNNING CURRENT - The current that flows through a load after inrush current. Usually
called "full load current".
RUNNING TIME - Amount of time a condensing unit is run per hour or per 24 hours.
RUST - A visible corrosion product consisting of hydrated oxides of iron. Applied only to
ferrous alloys.
RYZNAR STABILITY INDEX - An index based on calcium carbonate pH of saturation vs.
actual pH to determine scaling or corrosion tendencies of a water (R.I. = 2 pHs).
SACRIFICIAL ANODES - Coupling of a more active metal to a structure resulting in a
galvanic current flow through the corroding electrolyte.
SACRIFICIAL PROTECTION - Reduction of corrosion of a metal in an electrolyte by
galvanically coupling it to a more anodic metal. A form of cathode protection.
SADDLE VALVE (TAP-A-LINE) - Valve body shaped so it may be silver brazed or clamped
onto a refrigerant tubing surface.
SADDLE VALVE (TAP-A-LINE) - Valve body shaped so it may be silver brazed or clamped
onto a refrigerant tubing surface.
SAFETY CAN - Approved container of not more than 5 gallon capacity. It has a spring
closing lid and spout cover. It is designed to relieve internal pressure safely when exposed
to fire.
SAFETY CONTROL - Device to stop refrigerating unit if unsafe pressure and/or
temperatures and/or dangerous conditions are reached.
SAFETY PLUG - Device which will release the contents of a container before rupture
pressures are reached.
SALINITY - A measure of the concentration of dissolved mineral substances in water.
SALT SPITTING - The ability of an anion exchanger to convert a salt solution to caustic;
the ability of a cation exchanger to convert a salt solution to acid.
SATURATED AIR - When the air cannot hold any more moisture.
SATURATED LIQUID - A liquid which is at saturation pressure and saturation temperature;
in other words, a liquid which is at its boiling point for any given pressure.SATURATED VAPOR - A vapor which is at saturation pressure and saturation temperature.
A saturated vapor cannot be superheated as long as it is in contact with the liquid from
which it is being generated.
SATURATION - Condition existing when substance contains all of another substance it can
hold for that temperature and pressure.
SATURATION INDEX - The relation of calcium carbonate to the pH, alkalinity, and hardness
of a water to determine its scale forming tendency.
SATURATION PRESSURE - The point, where at a given temperature a pure substance
starts to boil.
SATURATION TEMPERATURE - The point, where at a given pressure a pure substance
starts to boil.
SAYBOLT UNIVERSAL VISCOSITY - A commercial measure of viscosity expressed as a time
in seconds required for 60 mL of a fluid to flow through the orifice of the standard Saybolt
universal viscometer at a given temperature under specific conditions; used for the lighter
petroleum products and lubrication oils.
SCALE - Surface oxidation, consisting of partially adherent layers of corrosion products,
left on metals by heating or casting in air or in other oxidizing atmosphere. Also a deposit
on a heat-transfer surface resulting from precipitation of salts present in water in contact
with that surface, forming a hard, dense material.
SCALE CAUSING ELEMENTS - Calcium and magnesium elements forming scale.
SCALE REMOVAL - Waterside, removal of scale using either the mechanical, the water
treatment or the acid cleaning process.
SCC - Stress corrosion cracking.
SCREENS - Equipment designed to prevent larger objects to enter water treatment
system.
SCREW PUMP - Compressor constructed of two mated revolving screws.
SCRUBBER - An apparatus for the removal of solids from gases by entrainment in water.
SEAL, MAGNETIC - A seal that uses magnetic material, instead of springs or bellows, to
provide the closing force.
SEAL, ROTARY - A mechanical seal that rotates with a shaft and is used with a stationary
mating ring.
SECOND LAW OF THERMODYNAMICS - Heat will flow only from material at higher
temperature to material at lower temperature.
SECONDARY REFRIGERANT - Chilled liquid-like water, which is circulated to distance units
where air is to be cooled in individual rooms.
SECONDARY SYSTEM - A re-circulating water system that is a takeoff from a primary
system; it does not circulate directly through the source of heat or cooling but only
indirectly through a heat exchanger.SECONDARY TREATMENT - Treatment of boiler feedwater or internal treatment of boiler
water after primary treatment.
SEDIMENTATION - Gravitational settling of solid particles in a liquid system.
SEEBECK EFFECT - When two different adjacent metals are heated, an electric current is
generated between the metals.
SENSIBLE HEAT - Heat which causes a change in temperature of a substance.
SENSIBLE HEAT - Sensible heat is any heat transfer that causes a change in temperature.
Heating and cooling of air and water that may be measured with a thermometer is
sensible heat. Heating or cooling coils that simply increase or decrease the air temperature
without a change in moisture content are examples of sensible heat.
SENSIBLE HEAT FACTOR - The ratio of sensible heat to total heat.
SENSING DEVICE - A device that keeps track of the measured condition and its
fluctuations so that when sufficient variation occurs it will originate the signal to revise the
operation of the system and offset the change. Example: a thermostat "bulb". A sensing
de vice may be an integral part of a controller.
SENSING ELEMENT - The first system element or group of elements. The sensing element
performs the initial measurement operation.
SEPARATOR - A tank type pressure vessel installed in a steam pipe to collect condensate
to be trapped off and thus providing comparatively dry steam to the connected machinery.
SEPARATOR - Device to separate one substance from another.
SEQUENCER - A mechanical or electrical device that may be set to initiate a series of
events and to make the events follow in sequence.
SEQUESTER - To form a stable, water-soluble complex.
SEQUESTRANT - A substance that holds a mineral or metal in solution beyond its
saturation point.
SERIES CIRCUIT - One with all the elements connected end to end. The current is the
same throughout but the voltage can be different across each element.
SERVICE DROP - The overhead service wires that serve a building.
SERVICE SWITCH - Disconnect switches or circuit breakers. Purpose is to completely
disconnect the building from the electric service.
SERVICE VALVE - Manually operated valve mounted on refrigerating systems used for
service operation.
SET POINT - The value of the controlled condition at which the instrument is set to
operate.
SETTLING BASIN - A containment design with external water treatment to settle
sediments and to clarify.
SHAFT SEAL - Device used to prevent leakage between shaft and housing.SHARP FREEZING - Refrigeration at temperatures slightly below freezing, with moderate
air circulation.
SHEAR PIN COUPLING -
SHED - To de-energize a load in order to maintain a kW demand set point.
SHED MODE - A method of demand control that reduces kW demand through shedding
and restoring loads.
SHELL AND TUBE FLOODED EVAPORATOR - Device which flows water through tubes built
into cylindrical evaporator or vice versa.
SHELL TYPE CONDENSER - Cylinder or receiver which contains condensing water coils or
tubes.
SHELL-AND-TUBE - Designation of a heat exchanger having straight tubes encased inside
a shell.
SHIELDED CABLE - Special cable used with equipment that generates a low voltage
output. Used to minimize the effects of frequency "noise" on the output signal.
SHOCK DOSAGE - The feeding of treatment to a system all in one slug or dose rather than
gradually (also called a slug dosage).
SHOCK FEEDER - A device which is used to add treatment to a system in an instantaneous
manner.
SHORT CIRCUIT - A direct connection of low resistive value that can significant alter the
behavior of an element or system.
SHORT CYCLING - Unit runs and then stops at short intervals; generally this excessive
cycling rate is hard on the system equipment.
SHROUD, TURBINES - Also referred to as the sealing strip on turbine blades. Its purpose is
to supply rigidity to the blades, lessen vibration and provide sealing between stages.
SHROUD, PUMPS - The front and/or back of an impeller.
SHUNT - A device to divert part of an electric current.
SIGHT GLASS - Glass tube or glass window in refrigerating mechanism. It shows amount
of refrigerant or oil in system and indicates presence of gas bubbles in liquid line.
SILICA - Silicon dioxide (Si02), a mineral found naturally as quartz or in complex
combination with other elements such as silicates.
SILICA GEL - Absorbent chemical compound used as a drier. When heated, moisture is
released and compound may be reused.
SILICA, COLLOIDAL - Silica in colloidal form.
SILICA, VOLATILE - Silica carryover with steam.
SILT DENSITY INDEX - A measure of the tendency of a water to foul a reverse osmosis
membrane, based on time flow through a membrane filter at constant pressure.SIMPLE CYCLE - Referring to the gas turbine cycle consisting only of compression,
combustion and expansion.
SINGLE PHASING - The condition when one phase of a multiphase (poly-phase) motor
circuit is broken or opened. Motors running when this occurs may continue to run but with
lower power output and over heating.
SINGLE SHAFT GAS TURBINE - A gas turbine arrangement in which the compressor and
the gas turbine are all coupled to one shaft.
SINGLE STAGE COMPRESSOR - Compressor having only one compressive step between
inlet and outlet.
SKIN CONDENSER - Condenser using the outer surface of the cabinet as the heat radiating
medium.
SLIME - A soft, sticky, mucus-like substance, originating from a bacterial growth.
SLING PSYCHROMETER - Measuring device with wet and dry bulb thermometers. Moved
rapidly through air it measures humidity.
SLUDGE - A deposit on a heat-transfer surface that does not have the hard, crystalline
structure of a scale but is softer and less dense.
SLUG - A unit of measure for mass in the English system, which equals 14.6 kg in the SI
system.
SLUGGING - Condition in which mass of liquid enters compressor causing hammering.
SLURRY - A water containing high concentration of suspended solids, usually over 5000
mg/L.
SLURRY EROSION - Material removal due to the combined action of corrosion and wear.
SODA ASH - A common water treatment chemical, sodium carbonate.
SODIUM CHLORIDE - Common table salt, used to produce a brine solution, used a
secondary refrigerant.
SODIUM SULFITE (Na2S03) - A chemical used with water treatment to remove small
amounts of oxygen.
SODIUM TRACER METHOD - A technique used to measure dissolved solids in steam to
values as low as 0.001 ppm.
SODIUM ZEOLITE SOFTENING - The process of removing scale forming ions of calcium and
magnesium and replacing them with the equivalent amount of sodium ions.
SOFT WATER - Water that is free of magnesium or calcium salts.
SOFTENING - The removal of hardness (calcium and magnesium) from water.
SOLAR HEAT - Heat created by visible and invisible energy waves from the sun.
SOLENOID VALVE - Electromagnet with a moving core. It serves as a valve or operates a
valve.SOLID ABSORBENT REFRIGERATION - Refrigeration system which uses solid substance as
absorber of the refrigerant during the cooling part of the cycle and releases refrigerant
when heated during generating part of cycle.
SOLID STATE HALOGEN LEAK DETECTOR - An electronic leak detector for all halogen.
related refrigerants.
SOLUBLE IRON - Usually present in cooling water systems and can arise from metallurgical
corrosion.
SOLU-BRIDGE - An electronic instrument used to measure conductivity of a water sample
to determine the dissolved solids content.
SOUR GAS - A gaseous environment containing hydrogen sulfide and carbon dioxide in
hydrocarbon reservoirs.
SOUR WATER - Waste water containing malodorous materials, usually sulfur compounds.
SPARGER - An extension into the bottom of a tank of a pipe which has a distribution nozzle
on the end for mixing one fluid with another.
SPECIFIC CONDUCTANCE - Measures the ability of a water to conduct electricity.
Conductivity increases with total dissolved solids and is therefore used to estimate
dissolved solids present in the water.
SPECIFIC GRAVITY - The density of a substance compared to the density of a standard
material such as water.
SPECIFIC HEAT - Ratio of quantity of heat required to raise temperature of a body 1
degree to that required to raise temperature of equal mass of water 1 degree.
SPECIFIC HEAT (Cp) - The ratio of the mount of heat required to raise a mass of material
1 degree in temperature to the amount required to raise equal mass of reference
substance, usually water, 1 degree in temperature.
SPECIFIC HUMIDITY - Ratio of weight of vapor to the weight of gas in a unit volume of an
air-water vapor mixture.
SPECIFIC VOLUME - Volume per unit mass of a substance.
SPEED GOVERNING -
SPLASH SYSTEM, OILING - Method of lubricating moving parts by agitating or splashing oil
in the crankcase.
SPLIT-STREAM DEALKALIZER - Where the flow of water is divided through a parallel
arrangement of hydrogen and sodium cat ion exchanger. The combined product being soft
and low in alkalinity.
SPRAY CARRYOVER - Are referred to a mist or fog and are a degree of atomization of the
boiler water and carried with the steam. This type of carryover is to be prevented by the
drum internals.
SPRAY COOLING - Method of refrigerating by spraying expendable refrigerant or by
spraying refrigerated water.SPRAY MANIFOLD - A pipe, or extension of a water line, that has several openings fitted
with nozzles which spray water.
SPRAY-COIL UNIT - A cooling circuit that sprays water over cooling coils through inflowing
air to humidify or dehumidify that air, as required.
SPRAY-COOLING CIRCUIT - An open cooling-water circuit which sprays water and cools by
evaporation, for example, a cooling tower, all evaporative condenser, an air washer, or a
spray-coil unit.
Spread: The divergence of the air stream in a horizontal or vertical plane after it leaves
the outlet.
STABILITY INDEX - An imperical modification of the saturation index used to predict
scaling or corrosive tendencies in water systems.
STAINLESS STEEL -
STANDARD AIR CONDITIONS - Standard air density has been set at 0.075 Ib/cu ft. This
corresponds approximately to dry air at 70°F and 29.92 in Hg. In metric units, the
standard air density is 1.2041 kg/m3 at 20°C and at 101.325 kPa.
STANDARD CONDITIONS - The standard conditions referred to in environmental system
work for air are: dry air at 70°F and at an atmospheric pressure of 29.92 inches mercury
(in Hg). For water, standard conditions are 68°F at the same barometric pressure. At
these standard conditions, the density of air is 0.075 pounds per cubic feet and the density
of water is 62.4 pounds per cubic foot.
STATE - Refers to the form of a fluid, either liquid, gas or solid. Liquids used in
environmental systems are water, thermal fluids such as ethylene glycol solutions, and
refrigerants in the liquid state. Gases are steam, evaporated refrigerants and the air-water
vapor mixture found in the atmosphere. Some substances, including commonly used
refrigerants, may exist in any of three states. A simple example is water, which may be
solid (ice), liquid (water), or gas (steam or water vapor).
STATIC HEAD - The pressure due to the weight of a fluid above the point of measurement.
STATIC SUCTION HEAD - The positive vertical height in feet from the pump centerline to
the top of the level of the liquid source.
STATIC SUCTION LIFT - The distance in feet between the pump centerline and the source
of liquid below the pump centerline.
STEAM - Water in vapor state.
STEAM DRUM - A pressure chamber located at the upper extremity of a boiler circulatory
system, in which the steam is generated in the boiler and separated from the water.
STEAM JET REFRIGERATION - Refrigerating system which uses a steam venturi to create
high vacuum (low pressure) on a water container causing water to evaporate at low
temperature.
STEAM PURITY - Refers to all matter but water in the steam.
STEAM QUALITY - The percentage by weight of vapor in a steam and water mixture.STEAM-ABSORPTION CONDENSER - That part of a steam-absorption machine in which the
water refrigerant is condensed by cooling-tower water and returned to the evaporator or
chiller.
STEAM-ABSORPTION MACHINE - A refrigeration or air-conditioning machine which uses,
as a refrigerant, water evaporated by absorption in a brine regenerated by steam and
condensed by cooling-tower water.
STICTION (STATIC FRICTION) - Resistance of start of motion.
STOICHIOMETRIC - The ratio of chemical substances reacting in the water that correspond
to their combining weights in the theoretical chemical reaction.
Stratified Air: Unmixed air in a duct that is in thermal layers that have temperature
variations of more than five degrees.
STRESS RAPTURE - A general type of damage referring to carbon steel tubing, when
heated above 450°C. Material will plastically deform (creep) and then rapture.
STUFFING BOX - That portion of the pump which houses the packing or mechanical seal,
The stuffing box is usually referred to as the dry portion of the pump, and is located in
back of the impeller and around the shaft.
SUBCOOLING - The difference between the temperature of a pure condensable fluid below
saturation and the temperature at the liquid saturated state, at the same pressure.
SUBCOOLING - The process of cooling a liquid to a temperature below its saturation
temperature for any given saturation pressure.
SUBLIMATION - A change of state directly from solid to gas without appearance of liquid.
SUBLIMATION - Condition where a substance changes from a solid to a gas without
becoming a liquid.
SUCTION HEAD - The positive pressure on the pump inlet when the source of liquid supply
is above the pump centerline.
SUCTION LIFT - The combination of static suction lift and friction head in the suction
piping when the source of liquid is below the pump centerline.
SUCTION LINE - Tube or pipe used to carry refrigerant gas from evaporator to
compressor.
SUCTION PRESSURE - Pressure in low-pressure side of a refrigerating system.
SUCTION PRESSURE CONTROL VALVE - Device located in the suction line which maintains
constant pressure in evaporator during running portion of cycle.
SUCTION PRESSURE CONTROL VALVE - Device located in the suction line which maintains
constant pressure in evaporator during running portion of cycle.
SUCTION SERVICE VALVE - Two-way manually operated valve located at the inlet to
compressor. It controls suction gas flow and is used to service unit.
SUCTION SIDE - Low-pressure side of the system extending from the refrigerant control
through the evaporator to the inlet valve of the compressor.SULFATE - A compound, ion, or salt of sulfur and oxygen, such as sodium sulfate
(Na2S04).
SULFITE DECOMPOSITION - Sodium sulfite, which is used as an oxygen scavenger, may
decomposes with higher temperatures and concentration. The decomposition results in
forming sulfur dioxide and thus leading to an acidic anhydride causing corrosion.
SULFONIC - A specific acidic group (SO3H) on which depends the exchange activity of
certain cation adsorbents.
SULFUR DIOXIDE (SO2 ) - An old refrigerant.
SUN EFFECT - Solar energy transmitted into space through windows and building
materials.
SUPERHEAT - The heat added to a fluid above its saturation point.
SUPERHEATED STEAM - Steam heated above its saturation temperature.
SUPERHEATED VAPOR - A vapor which is not about to condense.
SUPERHEATER - Heat exchanger arranged to take heat from liquid going to evaporator
and using it to superheat vapor leaving evaporator.
SUPERHEATING - The process of adding heat to a vapor in order to raise its temperature
above saturation temperature. It is impossible to superheat a saturated vapor as long as it
is in contact with the liquid from which it is being generated; hence the vapor must be led
away from the liquid before it can be superheated.
SUPERSATURATED SOLUTION - A solution of a salt or mineral with a concentration beyond
the normal saturation point.
SURFACE BLOWDOWN - Removal of water, foam, etc. from the surface at the water level
in a boiler.
SURFACE HEATING - The exterior surface of a heating unit. Extended heating surface (or
extended surface), consisting of fins, pins, or ribs which receive heat by conduction from
the prime surface. Prime surface: heating surface having the heating medium on one side
and air (or extended surface) on the other.
SURFACE-SPRAY UNIT - A spray-coil unit.
SURFACTANT - A compound that affects interfacial tension between two liquids. It usually
reduces surface tension.
SURFACTANTS - A wetting agent used to prevent fouling, mainly in water cooling systems.
SURGE - The sudden displacement or movement of water in a closed vessel or drum.
SURGE SURPRESSOR - A device that reduces harmonic distortion in line voltage circuits by
clipping off transient voltages which are fed through the power lines from operating
equipment.
SURGE TANK - Container connected to the low-pressure side of a refrigerating system
which increases gas volume and reduces rate of pressure change.
SUSPENDED SOLIDS - Un-dissolved solids in boiler water.SWAMP COOLER - Evaporative type cooler in which air is drawn through porous mats
soaked with water.
SWELLING - The expansion of an ion-exchange which occurs when the reactive groups on
the resin are converted from one form to another.
SYNERGISM - The combined action of several chemicals which produce an effect greater
than the additive effects of each.
SYSTEM - A series of ducts, conduits, elbows, branch piping, etc. designed to guide the
flow of air, gas or vapor to and from one or more locations. A fan provides the necessary
energy to overcome the resistance to flow of the system and causes air or gas flow
through the system. Some components of a typical system are louvers, grilles, diffusers,
filters, heating and cooling coils, air pollution control devices, burner assemblies, volume
flow control dampers, mixing boxes, sound attenuators, the ductwork and related fittings.
SYSTEM, CENTRAL FAN - A mechanical, indirect system of heating, ventilating, or air
conditioning, in which the air is treated or handled by equipment located outside the
rooms served, usually at a central location, and conveyed to and from the rooms by
means of a fan and a system of distributing ducts.
SYSTEM, CLOSED - A heating or refrigerating piping system in which circulating water or
brine is completely enclosed, under pressure above atmospheric, and shut off from the
atmosphere except for an expansion tank.
SYSTEM, DUCT - A series of ducts, conduits, elbows, branch piping, etc. designed to guide
the flow of air, gas or vapor to and from one or more locations. A fan provides the
necessary energy to overcome the resistance to flow of the system and causes air or gas
to flow through the system. Some components of a typical system are louvers, grilles,
diffusers, filters, heating and cooling coils energy recovery de vices, burner assemblies,
volume dampers, mixing boxes, sound attenuators, the ductwork and related fittings.
SYSTEM, FLOODED - A system in which only part of the refrigerant passing over the heat
transfer surface is evaporated, and the portion not evaporated is separated from the vapor
and recirculated.
SYSTEM, UNITARY - A complete, factory-assembled and factory-tested refrigerating
system comprising one or more assemblies which may be shipped as one unit or
separately but which are designed to be used together.
SYSTEMS CURVE - A graphic presentation of the pressure vs. volume flow rate
characteristics of a particular system.
TAlL PIPE - Outlet pipe from the evaporator.
TANDEM COMPOUND TURBINE - turbines are large turbines consisting of two or more
turbines in series coupled together as one shaft and applied to one generator
TANNINS - A chemical used as an inhibitor in relation with caustic embrittlement.
TEMPERATURE - Degree of hotness or coldness as measured by a thermometer.
TEMPERATURE CONTROL - Temperature-operated thermostatic device which automatically
opens or closes a circuit.
TEMPERATURE CRITICAL - The saturation temperature corresponding to the critical state
of the substance at which the properties of the liquid and vapor are identical. Temperature, Absolute Zero: The zero point on the absolute temperature scale, 459.69
degrees below the zero of the Fahrenheit scale, 273.16 degrees be low the zero of the
Celsius scale.
TEMPERATURE, DEWPOINT - The temperature at which the condensation of water vapor in
a space begins for a given state of humidity and pressure as the temperature of the vapor
is reduced. The temperature corresponding to saturation (100 percent relative humidity)
for a given absolute humidity at constant pressure.
TEMPERATURE, DRYBULB - The temperature of a gas or mixture of gases indicated by an
accurate thermometer after correction for radiation.
TEMPERATURE, EFFECTIVE - An arbitrary index which combines into a single value the
effect of temperature, humidity, and air movement on the sensation of warmth or cold felt
by the human body. The numerical value is that of the temperature of still, saturated air
which would induce an identical sensation.
TEMPERATURE, SATURATION - The temperature at which no further moisture can be
added to the air water vapor mixture. Equals dew point temperature.
TEMPERATURE, WET BULB - Thermodynamic wet bulb temperature is the temperature at
which liquid or solid water, by evaporating into air, can bring the air to saturation
adiabatically at the same temperature. Wet bulb temperature (without qualification) is the
temperature indicated by a wet bulb psychrometer constructed and used according to
specifications.
TEMPERATURE-HUMIDITY INDEX - Actual temperature and humidity of air sample
compared to air at standard conditions.
TENSILE STRENGTH - In tensile testing, the ratio of maximum load to original cross
sectional area. Also called ultimate strength.
TENSILE STRESS - A stress that causes two parts of an elastic body, on either side of a
typical stress plane, to pull apart.
TENSION - The force or load that produces elongation.
TERMINAL VELOCITY - The maximum air stream velocity at the end of the throw.
THE FIRST LAW - (1 ) When work is expanded in generating heat, the quantity of heat
produced is proportional to the work expended; and, conversely, when heat is employed in
the performance of work, the quantity of heat which disappears is proportional to the work
done (Joule); (2) If a system is caused to change from an initial state to a final state by
adiabatic means only, the work done is the same for all adiabatic paths connecting the two
states (Zemansky); (3) In any power cycle or refrigeration cycle, the net heat absorbed by
the working substance is exactly equal to the net work done.
The Second Law: (1) It is impossible for a self acting machine, unaided by any external
agency, to convey heat from a body of lower temperature to one of higher temperature
(Clausius); (2) It is impossible to derive mechanical work from heat taken from a body
unless there is available a body of lower temperature into which the residue not so
Therm - Measurement used by gas utilities for billin3 purposes. 1 Therm = 100 cubic feet
of gas = 100,000 Btu.
THERM - Quantity of heat equal to 100000 Btu.THERMAL CONDUCTIVITY - The rate at which heat is transferred through an object.
THERMAL CONDUCTIVITY - The rate of heat flow, under steady conditions, through unit
area, per unit temperature gradient in the direction perpendicular to the area. It is given
in the SI nits s watts per meter Kelvin (W/m • K).
THERMAL EFFICIENCY - Ratio of shaft work out of a system to the heat energy into the
system.
THERMAL EFFICIENCY OF A GAS TURBINE - Is the energy output of the gas turbine
divided by the energy input of the gas turbine.
THERMAL ELECTROMOTIVE FORCE - The electromotive force generated in a circuit
containing two dissimilar metals when one junction is at temperature different from that of
the other. (see also thermocouple).
THERMAL EQUILIBRIUM - When two bodies originally at different temperatures, have
attained the same temperature
THERMAL EXPANSION - The change in length of a material with change in temperature.
Thermal Expansion Valve: The metering device or flow control which regulates the amount
of liquid refrigerant which is allowed to enter the evaporator.
THERMAL SHOCK - The development of a steep temperature gradient and accompanying
high stress within a material or structure.
THERMAL TREATMENT - Refers to the treatment of water with heat to drive off the
dissolved gases and soften certain minerals for easy removal.
THERMISTOR - A two-terminal semiconductor device whose resistance is temperature
sensitive.
THERMOBANK - A bank for storing heat.
THERMOCOUPLE - Device for measuring temperature utilizing the fact that an
electromotive force is generated whenever two junctions of two dissimilar metals in an
electric circuit are at different temperature levels.
THERMOCOUPLE - Device which generates electricity, using the principle that if two unlike
metals are welded together and junction is heated, voltage will develop across the open
ends.
THERMOCOUPLE - Device which generates electricity, using the principle that if two unlike
metals are welded together and junction is heated, voltage will develop across the open
ends.
THERMOCOUPLE THERMOMETER - Electrical instrument using thermocouple as source of
electrical flow, connected to millimeter calibrated in temperature degrees.
THERMODISK DEFROST CONTROL - Electrical switch with bimetal disk controlled by
temperature changes.
THERMODYNAMIC CYCLE -
THERMODYNAMIC PROPERTIES - Basic qualities used in defining the condition of a
substance, such as temperature, pressure, volume, enthalpy, entropy. THERMODYNAMICS - Part of science which deals with the relationships between heat and
mechanical action.
THERMOELECTRIC REFRIGERATION - Where refrigeration is produced by the passage of
electric current through two dissimilar materials.
THERMOELECTRICITY - In physics, electricity generated by the application of heat to the
junction of two dissimilar materials. If two wires of different materials are joined at their
ends and one end is maintained at a higher temperature than the other, a voltage
difference will arise, and an electric current will exist between the hot and the cold
junctions.
THERMOMETER - Device for measuring temperatures.
THERMOMODULE - Number of thermocouples used in parallel to achieve low temperatures.
THERMOPILE - Number of thermocouples used in series to create a higher voltage.
THERMOSTAT - Device, which senses ambient temperature, conditions and, in turn, acts to
control a circuit.
THERMOSTATIC CONTROL - Device which operates system or part of system based on
temperature change.
THERMOSTATIC VALVE - Valve controlled by temperature change response elements.
THERMOSTATIC WATER VALVE - Valve used to control flow of water through system,
actuated (made to work) by temperature difference. Used in units such as water-cooled
compressor and/or condenser.
THREE-WAY VALVE - Multi-orifice (opening) flow control valve with three fluid flow
openings.
THRESHOLD TREATMENT - Chemical treatment, used to prevent scale formation, which
acts to hold hardness in solution at the threshold of precipitation.
THROTTLE GOVERNING - With throttle governing a single large control valve controls the
load from 0% to 100%When steam is throttled, the superheat increases and the turbine
exhaust steam is drier, reducing the turbine blade erosion, but with the drier steam
entering the condenser, the condenser losses increase. Throttling of steam through a valve
is an isenthalpic ( constant enthalpy ) process and no heat is lost. The so-called throttling
losses occur in the condenser.
THROTTLING - An irreversible adiabatic steady flow process in which the fluid is caused to
flow through an obstruction in a pipe with a resulting drop in pressure.
THROTTLING RANGE - The amount of change in the variable being controlled to make the
controlled device more through the full length of its stroke.
THRUST COLLAR POSITION INDICATOR - The axial position of the rotor is very important
and an axial position indicator is often applied to the thrust bearing.
It may be a large dial micrometer with alarm setting for an axial movement of 0.4
millimeter and shutdown at 0.8 millimeter, or An oil pressure gauge connected to an oil
leak-off device may also be used as an axial position indicator. The oil is supplied at say
500 kPa, flows through an orifice and leaks off through a nozzle. The pressure between
the orifice and nozzle depends on the distance between the nozzle and shaft thrust collar; the larger the distance the lower the pressure. The pressure gauge can be calibrated in
millimeter clearance and may have alarm and shutdown settings
TIMER-THERMOSTAT - Thermostat control which includes a clock mechanism. Unit
automatically controls room temperature and changes temperature range depending on
time of day.
TIP SEALED BLADES -
TITRATION - A chemical process used in analyzing feed water.
TON REFRIGERATION UNIT - Unit which removes same amount of heat in 24 hours as
melting of 1 ton of ice.
TON'S OF REFRIGERATION - The capacity of a refrigeration system that can freeze 1 ton
(1000 kg) of liquid water at 0°C into ice at 0°C in 24 hour is said to be 1 tone.
TOOL STEEL - Any steel used o make tools for cutting, forming, or otherwise shaping a
material into a final part.
TOPPING TURBINE - Have been used when old boilers are replaced with new high
pressure boilers. The turbine is a backpressure turbine exhausting to the old boiler header
still supplying steam to the old lower pressure turbines.
TOTAL DYNAMIC HEAD - Dynamic discharge head (static discharge head, plus friction
head, plus velocity head) plus dynamic suction lift, or dynamic discharge head minus
dynamic suction head.
TOTAL HARDNESS - See Hardness.
TOTAL HEAT - Sum of both the sensible and latent heat.
TOTAL HEAT (ENTHALPY) - Total heat is the sum of the sensible heat and latent heat in an
exchange process. In many cases, the addition or subtraction of latent and sensible heat
at terminal coils appears simultaneously. Total heat also is called enthalpy, both of which
can be defined as the quantity of heat energy contained in that substance.
TOTAL SOLIDS - Are the sum of the dissolved and suspended solids.
TOWER FILL - The interior structure of a cooling tower over which the water flows.
TRACE CONSTITUENTS - Materials present at a concentration less than 0.01 mg/L.
TRANSMITTANCE, THERMAL (U FACTOR) - The time rate of heat flow per unit area under
steady conditions from the fluid on the warm side of a barrier to the fluid on the cold side,
per unit temperature difference between the two fluids.
TRANSDUCER - The means by which the controller converts the signal from the sensing
device into the means necessary to have the appropriate effect on the controlled device.
For example, a change in air pressure in the pneumatic transmission piping.
TRANSFORMER - The system power supplying transformer is an inductive stationary
device which transfers electrical energy from one circuit to another. The transformer has
two windings, primary and secondary. A changing voltage applied to one of these, usually
the primary, induces a current to flow in the other winding. A coupling transformer
transfers energy at the same voltage; a step-down transformer transfers energy at a
lower voltage, and a step-up transformer transfers energy at a higher voltage. TRANSIENT CONSTITUENTS - Are those constituents which change in concentration or
activity by changes in the aquatic environment. The change my be due to oxidation
potentials, biological activities, etc..
TRANSISTOR - An active semiconductor device capable of providing power amplification
and having three or more terminals.
TREATMENT - A process whereby impurities are removed from water; also a substance
added to water to improve its physical or chemical properties.
TRIBOLOGY - The science concerned with the design, friction, lubrication and wear of
contacting surfaces that move relative to each other (as in bearings, cams, or gears).
TUBE SHEET - The portion of a heat exchanger or boiler in to which the tubes are rolled or
secured.
TUBERCLE - A protective crust of corrosion products (rust) which builds up over a pit
caused by the loss of metal due to corrosion.
TUBERCULATION - A corrosion process that produces hard knob-like mounds of corrosive
products on metal surfaces, increasing friction and reducing flow in a water distribution
system.
TUBE-WITHIN-A-TUBE - Water-cooled condensing unit in which a small tube is placed
inside large unit. Refrigerant passes through outer tube, water through the inner tube.
TURBIDITY - The measure of suspended matter in, a water sample which contributes to
the reflection of light or cloudiness.
TURBIDITY UNIT - The unit of measure of suspended matter in water. It is the measure of
light compared against light reflected by a reference standard as defined by the standard
methods of water analysis in, APHA.
TURBINE METER - A device used to measure water consumption in industrial plants.
TURBINE ROTOR - The rotating assembly enclosed within the turbine casing
TURNER GAUGE - A device used to measure the actual scale-thickness in boiler tubes.
TWO-TEMPERATURE VALVE - Pressure-opened valve used in suction line on multiple
refrigerator installations, which maintains evaporators in a system at different
temperatures.
TWO-WAY VALVE - Valve with one inlet port and one outlet port.
ULTIMATE STRENGTH - The maximum stress (tensile, compressive or shear) a material
can sustain without fracture. It is determined by dividing maximum load by the original
cross-sectional area of the specimen.
ULTRA FILTRATION - A process that forces water through a filtering membrane by means
of pressure gradients in order to obtain ultra pure water.
UNDER DEPOSIT ATTACK - Corrosion under or around a localized deposit on a metal
surface (a form of crevice corrosion).
UNITARY SYSTEM - A room unit which performs part or all of the air conditioning
functions. It may or may not be used with a central fan system. UNLOADER - A device in or on the compressor for equalizing high-side and low-side
pressures for a brief time during starting and for controlling compressor capacity by
rendering one or more cylinders ineffective.
UP FLOW - The operation of an ion-exchange unit in which solutions are passed in at the
bottom and out at the top of the container.
UP FLOW FILTER - A unit containing a single filter medium, usually with graded sand.
UP FLOW FURNACE - A furnace in which the heated air flows upward as it leaves the
furnace.
UPSTREAM - The inlet side of an instrument, a pump, valve, etc..
UTILITY TRANSFORMER - Primary and secondary coils of wire which reduce (step down)
the utility supply volt age for use within a facility.
U-TUBE MANOMETER - A U-shaped section of plastic or glass tubing that is partially filled
with water or mercury. They are used to measure the lower pressure ranges of gases.
VACUUM - Pressure lower than atmospheric pressure.
VACUUM BREAKER - A device to prevent a suction in a water pipe.
VACUUM PUMP - Special high efficiency device used for creating high vacuums for testing
or drying purposes.
VALVE, MODULATING - A valve which can be positioned anywhere between fully on and
fully off to proportion the rate of flow in response to a modulating controller (see
modulating control).
VALVE, NEEDLE - A form of globe valve that contains a sharp pointed, needle like plug that
is driven into the and out of a cone shaped seat to accurately control a relatively small
rate of flow of a fluid.
VALVE, POP - A spring loaded safety valve that opens automatically when pressure
exceeds the limits for which the valve is set. It is used a safety device on pressurized
vessels and other equipment to prevent damage from excessive pressure, also called relief
valve or a safety valve.
VALVE, POPPET - A device that controls the rate of flow of fluid in a line or opens or shuts
of the flow of fluid completely. When open, the sealing surface of the valve is moved away
from a seat. When closed, the sealing surface contacts the seat to shut of the flow. Poppet
valves are used extensively as pneumatic controls and as intake and exhaust valves in
most internal combustion engines.
VALVE, PRESSURE RELIEF - A valve designed to minimize the possibility of explosion when
air temperature surrounding a refrigeration system may rise to a point where the pressure
of the refrigerant gas to increase to a danger point.
VALVE, RELIEF - Also called pressure relief valve.
VALVE, TWO-POSITION - A valve which is either fully on or fully off with no positions
between. Also called an "on-off valve".
VANE - That portion of an impeller which throws the water toward the volute case.VAPOR - A gas, particularly one near to equilibrium with the liquid phase of the substance
and which does not follow the gas laws. Usually used instead of gas for a refrigerant, and,
in general, for any gas below the critical temperature.
VAPOR BARRIER - A moisture-impervious layer applied to the surfaces enclosing a humid
space to prevent moisture travel to a point where it may condense due to lower
temperature.
VAPOR LOCK - A condition where liquid flow is impeded by vapor trapped in a liquid line.
VAPOR PHASE -
VAPOR PHASE INHIBITORS - A system using an organic nitrite compound, a powder which
vaporizes slowly to protect ferrous metal from contact with oxygen.
VAPOR PRESSURE - Vapor pressure denotes the lowest absolute pressure that a given
liquid at a given temperature will remain liquid before evaporating into its gaseous form or
state.
VAPOR, SATURATED - Vapor in equilibrium with its liquid; i.e., when the numbers per unit
time of molecules passing in two directions through the surface dividing the two phases
are equal.
VAPOR, SUPERHEATED - Vapor at a temperature which is higher than the saturation
temperature (i.e., boiling point) at the existing pressure.
VAPOR, WATER - Water used commonly in air conditioning parlance to refer to steam in
the atmosphere.
VAPOROUS CARRYOVER - Referring to impurities carried over with the steam and then
forming a deposit on turbine bladings. This type of carryover is difficult to prevent.
VELOCITY - A vector quantity which denotes, at once, the time rate and the direction of a
linear motion.
VELOCITY COMPOUNDING -
VELOCITY HEAD - The vertical distance a liquid must fall to acquire the velocity with which
it flows through the piping system. For a given quantity of flow, the velocity head will vary
indirectly as the pipe diameter varies.
VELOCITY, TERMINAL - The highest sustained air stream velocity existing in the mixed air
path at the end of the throw.
VENT - An opening in a vessel or other enclosed space for the removal of gas or vapor.
VENTILATION - The process of supplying or removing air by natural or mechanical means,
to or from a space; such air may or may not have been conditioned.
VENTURI TUBE METER - A flow meter used to determine the rate of flow and employing a
venturi tube as the primary element for creating differential pressure in flowing gases or
liquids.
VISCOSITY - That property of semi-fluids, fluids, and gases by virtue of which they resist
an instantaneous change of shape or arrangement of parts. It is the cause of fluid friction
whenever adjacent layers of fluid move with relation to each other. VISCOSITY INDEX - A commonly used measure of the change in viscosity of a fluid with
temperature. The higher the viscosity index, the smaller the relative change in viscosity
with temperature.
VITAL HEAT - The heat generated by fruits and vegetables in storage; caused by ripening.
VOLATILE SOLIDS - Those solids in water or other liquids that are lost on ignition of dry
solids at 550°F.
VOLATILE TREATMENT - Based on the use of hydrazine and neutralizing amines or
ammonia. Leaves no solids in the boiler.
VOLATILITY - Volatility, surface tension and capillary action of a fluid are incidental to
environmental systems. Volatility is the rapidity with which liquids evaporates extremely
rapidly and therefore is highly volatile.
VOLT - The unit of potential difference or electromotive force in the meter-kilogram
second system, equal to the potential difference between two points for which 1 coulomb
of electricity will do 1 joule of work in going from one point to another.
VOLTAGE (E) - The electromotive force in an electrical circuit. The difference in potential
between two unlike charges in an electrical circuit is its voltage measured in "volts" (V).
VOLTAGE DROP - The voltage drop around a circuit including wiring and loads must equal
the supply volt age.
VOLTAIC CELL - A storage device that converts chemical to electrical energy.
VOLUME, SPECIFIC - The volume of a substance per unit mass; the reciprocal of density.
VOLUTE - The spiral-shaped casing surrounding a pump impeller that collects the liquid
discharged by the impeller.
WALK-IN-COOLER - A large commercial refrigerated space often found in supermarkets or
places for whole sale distribution.
WASTE WATER - The used water and solids from industrial processes that flow to a
treatment plant.
WATER - A tasteless, odorless, colorless liquid in its pure state.
WATER ABSORPTION - The amount of weight gain (%) experienced in a polymer after
immersion in water for a specific length of time under controlled environment.
WATER HAMMER - Banging of pipes caused by the shock of closing valves (faucets).
WATER LUBRICANT - Water used as a lubricant; for example, in a mechanical seal on a
centrifugal water pump.
WATER SEALED GLAND -
WATER SOFTENER - A device or system used to remove calcium and magnesium hardness
minerals from a water supply.
WATER TUBE - A boiler tube through which the fluid under pressure flows. The products of
combustion surround the tube.WATER VAPOR - In air conditioning, the water in the atmosphere.
WATER, BRAKISH - (1) Water having less salt than sea water, but undrinkable. (2) Water
having salinity values ranging from about 0.5 to 17 parts per thousand.
WATER, POTABLE - Water that is safe to drink.
WATER, SOUR - Waste waters containing fetid materials, usually sulfur compounds.
WATER-ICE REFRIGERATION SYSTEM - Heat is absorbed as ice melts and thus producing a
cooling effect.
WATER LEG - That space that is full of boiler water between two parallel plates. It usually
forms one or more sides of internally fired boilers.
WATER WALL - A row of water tubes lining a furnace or combustion chamber, exposed to
the radiant heat of the fire.
WATT (W) - A measure of electric power equal to a current flow of one ampere under one
volt of pressure; or one joule per second in SI units.
WEIGHT TO POWER RATIO - It is the weight of the machine producing work. For example
- the gas turbine is capable of producing more horse power per given mass of its
machinery, then the same amount of horse power produced by a machine having many
times that mass.
WET BULB - Device used in measurement of relative humidity. Evaporation of moisture
lowers temperature of wet bulb compared to dry bulb temperature in same area.
WET BULB TEMPERATURE (WB) - The temperature registered by a thermometer whose
bulb is covered by a saturated wick and exposed to a current of rapidly moving air. The
wet bulb temperature also represents the dew point temperature of the air, where the
moisture of the air condenses on a cold surface.
WET STANDBY - Boiler is filled completely with water or maintained at normal operating
level with a positive nitrogen pressure of 35 to 70 kPa.
WET-BULB DEPRESSION - The difference between the dry-bulb temperature and the wet
bulb temperature.
WIND AGE DRIFT - That water lost from an open re-circulating-water system by means of
wind blown through the spray area that carries water out of the system. This is not the
same as loss by evaporation, since such a loss can occur even without evaporation.
WOBBLE PLATE-SWASH PLATE - Type of compressor designed to compress gas, with
piston motion parallel to crankshaft.
WORKING FLUID - is the substance which does the work in a heat engine. The air is one of
the working fluids used with gas turbines. Freon's are the working fluids used with some
refrigeration systems. Water is the working fluid used with steam boilers.
ZEOLITE - A natural mineral (hydrous silicates) that has the capacity to absorb hardness,
calcium, and magnesium ions from water.
ZEOLITE SOFTENING - Refers to the process, where zeolite chemicals are capable to
exchange ions with the hardness causing impurities of the water.ZETA POTENTIAL - The difference in voltage between the surface of the diffuse layer
surrounding a colloidal particle and the bulk liquid beyond.
ZONING - The practice of dividing a building into small sections for heating and cooling
control. Each section is selected so that one thermostat can be used to determine its
requirements.