MARINE ENGINEERING PRACTICE MEP ORAL QUESTIONS AND ANSWER

CHAPTER-1

SHAFT SEALS AND PACKING

Oil Control Rings

In most reciprocating compressors these rings prevent crankcase oil from passing into the cylinder and in

some instances to prevent condensate and cylinder and packing lubricant from entering the crankcase.

In a crosshead type engine, this control is achieved through piston rod control /wiper rings. This contains

crankcase oil in the crankcase, the amount of oil entering the cylinder and consequently the gas stream is

controlled. Also prevents the gases and the cylinder oil mixture to enter the crankcase which is detrimental

to the bearings and other parts of the running gear if mixed with the crankcase oil. Segmental wiper rings

may be either radially or tangentially cut. They are garter spring actuated. The scraper edges in contact with

the piston rod are proportioned to give a bearing load sufficient to break the surface tension of the oil film

on the rod and wipe it away.

There are two types of Control / Wiper rings One is designed to turn back a large volume of oil along the

rod. The other type has drainage passages through which oil wiped from the rod drains into an annular area

around the outside of the rings and thence back into the crankcase. Normally two or three wipers are used in

an oil seal with a pressure packing.

Shaft Seals

Pumps having glands, require shaft seals to separate the fluid handled from the drive motor. Likewise, valves

transmitting fluid in a pipeline will also need a gland sealing around their stems, below the handwheels.

These seals can be simple or more sophisticated depending on the fluid they handle, the temperature and

pressures involved, the corrosive properties etc.; in its most complicated form it will constitute a hydraulic

seal (water or oil lubricated) at the ship's stern within and outside the ship o keep the seawater away.

Seal Terms

Bearing/Wear rings: Soft metal or plastic rings placed in grooves on the piston or in the head to prevent

contact between hard metal surfaces.

Durometer: A generic term referring to the instrument and the scale used to measure the relative hardness

of various elastomers. The lower the durometer reading, the softer the material.

Dynamic Seal: A sealing device used between mating surfaces that have relative motion.

Elastomer: A rubber-like material having the capacity for large deformation and rapid, recovery from the

deforming force.

Gland: A groove or open area machined into the head or piston that houses the sealing device.

Static Seal: A sealing device used between mating surfaces that have no relative motion.

Wiper/Scraper: A device placed in the head of a cylinder for the purpose of excluding foreign matter from

the inside of the cylinder.

Mechanical Seals

The maintenance free mechanical seal has virtually become standard equipment of glanded direct coupled

pumps.

They operate without any visible water leakage and do not require any maintenance whatsoever during their

service life, which runs between 1 and 2 years, maximum 3 years. However, extremely bad water (sediments,

additives, overheating) can also severely shorten their service life. In such cases it is advisable to check their

suitability or the necessity for special designs with the seal manufacturers.

The following mechanical seal configurations have proved to be the most suitable: bi-directional operation

• Flexible shaft attachment by means of an elastomeric bellows (automatic compensation of seal seat

wear by means of the integrated spring)

• Hard / soft material combination (ceramics or hardened metal to carbon) offering optimum

lubricating qualities.

• Attachment to a bronze or stainless steel shaft sleeve

Advantages of using mechanical seals

• Lower frictional drag than traditional packing means improved pump efficiency

• A mechanical seal will not wear out a shaft, or sleeve, as fast as packing rings

• Near zero leakage is possible with mechanical seal; packing requires some leakage (usually visible)

for proper lubrication

• Properly applied mechanical seals require less periodic maintenance than packing

• Specially designed mechanical seals can be applied to higher pressures and speeds than traditional

packing.

Disadvantages of using mechanical seals

• Less tolerant to shaft deflection and misalignment

• Less tolerant to dirty or contaminated liquid; will require cyclone separator to clean the liquid

• Require expensive seal piping to flush and quench

• Mechanical seals are more expensive than packing rings

Labyrinth Seals

Labyrinth Seal – (e.g., Turbocharger, Auxiliary Steam Turbine etc.)

The leakage of gas is reduced by the use of labyrinths, these provide a torturous path for the gas to follow to

exit the turbine reducing the pressure across a series of fine clearances Within the cavity where the flow is

turbulent, the velocity of the gas is increased with an associated drop in pressure. The kinetic energy is

dissipated by the change in direction, turbulence and eddy currents.

CHAPTER-2

HEAT EXCHANGERS

Heat Exchangers

Heat exchangers are used onboard to heat or cool process fluids. Heat transfer is achieved by circulating the

fluids in adjacent spaces in the heat exchanger. In a heat exchanger transfer of heat takes place between

fluids, from higher temperature fluid to a lower temperature fluid. Performance of heat exchanger should be

optimum for efficient running of the main engine, generators and other auxiliary machinery.

Heat exchangers are broadly classified into shell and tube type and plate type based on design and

construction. It is imperative that the heat exchanger is maintained in a good condition. Before carrying out

any maintenance routine, the maker's manual should be studied and thoroughly understood.

Before moving into details of maintenance, a class four engineer should be in a position to understand how

a shell and tube heat exchanger looks like

Checks and routines

Every day

• Check the temperature differential across the tube nest.

• Check the temperature differential across the shell.

15 days

• Open the inspection covers and check the tube side. Assess the fouling and plan for cleaning.

Three months once

• Carry out back flushing.

• Carry out circulation cleaning of the tubes .

6 months once

• Inspection of sacrificial anodes and their securing to end cover or water boxes. If found wasted,

replace the same.

• Inspection of sealing rings. If damaged or brittle replace the same.

• Mechanical cleaning tubes.

• Circulation cleaning on shell side or cleaning on outside tube surfaces.

Safe Isolation of the System Check List

• Shut the cooling or heating fluid such as sea water or steam.

• Shut the process fluids such as lubricating oil or fresh water.

• Confirm by opening the vent cock or purge valve that the cooler is isolated.

• Has the fluid been drained completely.

• Display 'men at work' warning board.

Shell and Tube Heat Exchangers Cleaning

Periodical preventive maintenance ensures trouble free performance of the heat exchanger. Maintaining the

heat exchanger in a clean condition ensures that the faults are detected at an early stage.

The fluid flows through the heat exchanger, even though the associated machinery is not running. For

instance, the main engine lube oil is circulated in the system even when the main engine is not running.

Hence, the maintenance of heat exchanger is carried out as per the specified time interval, performance and

not according to the running hours.

Before commencing the maintenance routines, it should be ensured that the heat exchanger is isolated, all

the pipeline valves are secured and a notice is displayed. The recommended maintenance schedule to be

carried out on the heat exchanger at particular time periods is listed

Physical cleaning of tubes

On board in a shell and tube heat exchanger the cooling fluid is usually sea water. Deposits and scales

accumulate on tube side which has to be physically cleaned. Manual cleaning of the seawater passages after

certain time period is the only remedy to improve the performance.

During the manual cleaning of the tubes, the end covers are removed and the brush with long handle is used

to remove the deposits.

1. Isolate the system. Make register marks on the end covers. Slacken the nuts in the end cover. Open

the end covers of the shell.

2. Take a close look at the end covers, division plate and sacrificial anodes.

3. Cleaning of seawater tubes is usually by mechanical cleaning. Special tools are provided by the

manufacturer, to remove scale and obstructions in the cooler tubes.

4. Thoroughly rinse with fresh water.

5. Replace the sacrificial anode, if it is wasted extensively.

6. Replace the joint in between the end cover and the shell.

7. Open the system valves and check for leaks. Shell side cleaning

Shell side cleaning

Cleaning of shell side is done by circulating with a de-grease solution or dismantling the entire heat

exchanger and immersing the tube stack in a tank containing cleaning solution. Usually go for maker

recommended de-greasing agents.

In case of Fresh Water medium to be cooled – use de-scaling liquid mixed in proportion with water for

chemical cleaning.

Circulation cleaning of tubes is carried out apart from back flushing of tubes. Use maker's recommended

chemicals. The chemicals are added to fresh water in recommended quantities and circulation of chemical

solution is carried out through the tubes. After stipulated time the tubes are rinsed with fresh water.

The tube outer surfaces in lube oil cooler or heavy oil heater are cleaned by circulating degreasing solution

recommended by the maker. Alternatively, the heat exchanger is dismantled and the tube stack is immersed

in a tank of cleaning solution.

For Circulation cleaning, isolate the system as follows, for Shell side

1. Make register marks and remove the shell side connecting pipes.

2. Prepare the de- greasing solution. Maker recommended chemical is mixed in correct quantity with

fresh water.

3. Connect the shell side to the inlet and outlet of circulating pump.

4. The circulation pump is started. It takes suction from the chemical tank. Chemical solution after

circulating through the shell side flows back to the reservoir.

5. It is always necessary to maintain the temperature of the chemical solution as per manufacturer's

recommendations.

6. After the stipulated time, remove the set up. Carry out fresh water rinsing and dry the same.

Back Flushing of Shell and Tube Heat Exchangers

Back flushing is a process used to remove the deposits in the inlet region by reversing the fluid flow for a

short period of time. This does not require dismantling of the coolers and can be carried out with less effort

than manual cleaning.

Cathodic Protection and Corrosion

Cathodic Protection

Corrosion should be avoided in a multi-tubular heat exchanger. Since the tubular heat exchanger is made up

of different materials, which are connected to each other in the presence of sea water, can lead to formation

of galvanic cells. Corrosion can be countered by providing cathodic protection.

Sacrificial anodes are fitted to the water boxes or end covers. As they are more prone to corrosion, they

inhibit corrosion of the tubes and baffles. Care should be taken such that electrical continuity is maintained

after fitting.

By fitting pure zinc or soft iron, inside water boxes, using a bolt or stud through the same material of the

water box, corrosion attack is prevented.

Since, zinc or soft iron is on the lower side of the galvanic series, than the parts of heat exchanger, the zinc

or soft iron takes up the corrosion, performing a sacrificial part. The sacrificial anode forms a passive oxide

film preventing corrosion.

Corrosion

In a heat exchanger, corrosion due to deposit attack is caused by a layer of non-adherent deposits settling

down in the lower half of the tubes. Due to deposits on lower half of the tubes, local difference in velocity

and temperature takes place.

The protective passive oxide film locally breaks down due to these deposits, leading to severe pitting

corrosion.

Chloride ion in sea water accelerates the pitting corrosion. Aluminium alloys can suffer severe pitting, due

to local cell formation between the anodic aluminium matrix and cathodic alloying elements such as copper

and nickel.

Electrical continuity is of paramount importance and continuity is established by “jump wire” or jump plate,

fitted between the tube plate and the water box flange or by using collar studs.

Areas prone to corrosion are water boxes, tube plates etc., and the inside of the water boxes are usually

coated with epoxy paints.

Dismantling, Tube replacement and assembling of cooler

1. Obtain a new set of jointing’s and O-rings before commencing to dismantle the cooler.

2. Isolate the unit by closing the appropriate valves, then drain off both fluids.

3. If it is oil cooler, then oil should be removed whilst it is warm.

4. File register marks across the edges of the cylinder, tube plate and water box flanges, to ensure correct

alignment when reassembling.

5. Remove metallic connector strip.

6. Unscrew the nuts and remove the fixed end water box.

7. Remove the joint ring.

8. Remove the expansion end box together with the machined leakage ring and two joint rings.

9. Remove the tube stack.

Tube stack removal procedure

1. Owing to the close manufacturing tolerances, it may be difficult to remove the tube stack from a unit.

2. On no account use levers under fixed end tube plate. This may damage the plate and cause leakage

when the unit is reassembled.

3. Release the stack from housing using jack bolts by evenly tightening the bolts diagonally. This has

to be done before making any arrangements for hoisting the stack.

4. Support the stack, if horizontal, with a leather sling of suitable strength for hoisting.

5. If the stack is vertical, support the stack with an eye-bolt for vertical hoisting.

6. A tapped hole is provided at the centre of each tube plate for the insertion of an eye-bolt.

7. Great care must be exercised to avoid damage to the stack during handing.

Tube Removal and Replacement

Adverse operating conditions or careless maintenance may be the cause of tube failure. Before carrying out

tube replacement. Go through the maker's instructions. Re-tubing tools are usually provided by the

manufacturer. So use the correct tools for the job.

• Fit the drill in the wrench. Fill the flutes of the drill with grease. Drill out the expanded section of the

tube, in the tube plate expansion end, until the tube is freed. Clear the burrs from the tube end.

• Remove drills and insert centralizing pin in the tube

• Drill out the tube end at the fixed end tube plate. Clear the burrs from the tube end. Put the drill back

in to the tube.

• Drive the centralizing pin as far as possible in to the tube plate at the expansion end.

• Lock the wrench over the drill at the fixed plate end.

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AJ NOTES 11

• Work out the tube carefully out of the stack from the fixed plate end

1. Clean the tube plate holes and insert the new tube. Secure the position of the tube at each end by

using taper drift

2. Insert the roller expander into thro tube. Rotate the expander in clockwise direction. Apply hand

pressure. Do not force the expander. Use expander at the other end.

Tube replacement using extension tools

1. Drill out each end of the defective tube using a special drill extension.

2. To remove the tube, screw the sections of the brush rod together and pass them through the tubes.

On one projecting end of the rod, screw the brush rod plug and, on the other, the brush rod handle

3. Pull steadily on the handle, rotating the tubes to ease through tight places. When the tube is clear of

the box, the wrench may be used.

4. Taper drift the new tube in position and roller expand at both ends.

Assembling the Cooler

• Ensure that all internal surfaces are clean.

• Pass the flat joint ring over the stack,

• Insert the stack into the shell. Be careful not to damage the tube stack.

• Align the register marks on the shell flange and the fixed end tube plate.

• Place a flat joint ring in position and mount the fixed end water box.

• The register marks should be in alignment.

• Secure by tightening the nuts.

• Clean the contacting surfaces to ensure a metal-to-metal contact.

• Fix the contactor strip.

• Place the expansion end inner joint ring, safety leakage ring and outer joint ring over the expansion

end tube plate.

• Mount the expansion end water box in position on the studs and secure by tightening all the nuts

progressively and evenly, to avoid local overstressing.

• Replace water box covers, inspection doors and drain plugs.

Testing

• Blank the shell side fluid entry and exit.

• Fill the shell side with fresh water.

• Apply the correct water pressure to the cooler and examine the tubes, plates, and joints for leakage.

• Should a newly fitted tube show signs of leakage at the tube to tube-plate joint, it is a general

procedure to re-expand lightly with the roller expander.

Leakage Detection and Tube plugging

Tubes are replaced in a heat exchanger provided that there is a complete tube failure. If a tube is found

leaking, the tube is plugged. However the procedure for leakage detection is shown below.

Leakage Detection in Shell and Tube Type Cooler

The working pressures in case of jacket water system or lubricating oil system are usually of higher pressure

than sea water system. If the leakage takes place in the jacket cooling water side or lubricating oil side, the

flow from any point of leakage is in to the sea water side of the cooler. If the leakage is heavy then, usual

indication is loss of jacket cooling water or lubricating oil.

Procedure:

Ensure the end covers are removed from the sea water box side and secure the tube stack by dog clamp

arrangement-tube stack should not be disturbed when shell is under pressure.

• Clean the sea water side of the cooler.

• Start the fresh water cooling pump or lubricating oil pump.

• Let the fluid circulate through the cooler spaces on the outside of the tubes.

• Leakage within the tubes or at the junction of the tube plate will show up as liquid trickling.

• Identify the tube which is leaking. It is a time consuming procedure so be patient.

Fluorescent Halo Test

Small leaks are extremely difficult to detect, especially if the time available is very less. Owing to paucity

of time it, will be difficult to get sea water cooling spaces dried out. The damp tube plates deter the small

amounts of leakage. If the leakage is very small and time availability is less then follow the below procedure:

• A small amount of fluorescent sodium crystals is dissolved in water within the space surrounding the

tubes.

• The tube plates are then viewed under a source of ultra violet light.

• Even very small leakage is sharply visible as a fluorescent halo.

Soap Bubble Test

If the time availability is high and if the heat exchanger can be isolated, then carry out then following

procedure:

• Ensure the end covers are removed from the sea water box side.

• Isolate the entire cooler and pressurize the shell side with air.

• Use soap solution and apply the same at the tube ends.

• Bubble formation will indicate the leaking tube.

Plugging the Tube

• Once the leaky tube is detected, measure the inside diameter of the tube and find suitable plugs for

plugging.

• For plugging the leaky tube or tubes, plugs made of brass [same material as the tubes] or plastic are

being used on either end of the leaky tube.

• Plug should be driven securely so as to isolate it completely.

• Carry out a leak test again to confirm that the leakage is arrested.

Maintenance Chart

Before commencing the maintenance routines, ensure that the heat exchanger is isolated, all the pipeline

valves are secured and a notice is displayed.

The checks and maintenance to be carried out on the heat exchanger at particular time intervals are listed

below:

Every day

• Check the temperature differential across the plate

• stack cold fluid side and hot fluid side.

Three months once or as per demand

• Carry out back flushing Assess the improvement after back flushing

• Carry out circulation cleaning of the cold fluid side and hot fluid side.

• Assess the improvement after cleaning.

6 months once or as per demand

• Inspection of sealing packing material If damaged or brittle replace the same.

• Mechanical cleaning of plates. Assess the improvement after cleaning.

Time Interval – Once a Year as a minimum

• Check temperature and flow against the commissioning data provided by the manufacturer.

• Check general condition and look for any signs of leakage.

• Wipe clean all painted parts and check surfaces for signs of damage – “touch up” if necessary.

• Check bolts and bars for rust and clean. Lightly coat threaded parts with molybdenum grease or with

a corrosion inhibitor (ensure that no grease, etc. falls onto the plate gaskets.

• If rollers are fitted to the follower frame plate, lubricate the bearings with light machine oil.

Back Flushing of Plate Type Heat Exchangers

Fouling and clogging of heat exchangers usually on the sea water side cause huge problems and down time.

The economic penalty for fouling are reduced thermal efficiency, increased pressure drop, additional

maintenance and loss of production due to down time.

Back-flushing is an easy and efficient method to prevent clogging and fouling of heat exchangers. The

cleaning effect is achieved by changing the flow of direction in the heat exchanger so that the dirt

accumulated in the inlet region and the heat exchanging channels is flushed out the same way as it entered.

Back flushing: The reversal of one or both fluid flows for short periods.

Plate type heat exchangers cleaning

Before cleaning isolate the heat exchanger by closing the appropriate valves. Measure the distance between

the two end plates (frame plate and pressure plate). Use the special spanner provided for slackening and

tightening. Slacken the nuts equally. because unequal slackening might cause permanent damage to the

plates. Ensure all the nuts are slackened and slide the pressure plate in the guide bar and start cleaning the

plates in the plate stack by hosing with fresh water and scrubbing them gently using soft brush provided.

Take special care such that rubber gaskets are not damaged. After through cleaning; slide the plates in the

guide bar. Use torque spanner and tighten the nuts on the tie-bolt equally. Measure the distance and confirm

the same from the values noted. Open the valves for cold fluid and let the fluid circulate for twenty minutes

and then open the valves for hot fluid. Check for leakages.

Suitable adhesive is used to bond nitrile seals. Removal is done by using liquid nitrogen which freezes and

makes the nitrile rubber seal brittle. Thus it results in contraction of rubber seal, which is then broken away.

Manual methods of seal removal will result in plate damage.

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AJ NOTES 15

If working temperatures are maintained higher than normal then the rubber hardens and loses its elasticity.

The joints are squeezed when the plates are assembled and clamping bolts are tightened after cleaning. Over

tightening can cause damage to plates and therefore, makers procedure has to be followed.

Before commencing the cooler stack, dimensions are checked and a torque spanner is used for tightening.

The attached photograph gives us an idea of assembled plate stack.

Tightening the Plate Pack

The plate pack length is stated on the drawing and on the type plate. Two lengths are given on some heat

exchangers. The larger one is the plate pack length for a heat exchanger with new gaskets. As the gaskets

age it may be necessary to tighten the plate pack further but never to the smaller of the two measurements.

The plates may be become damaged if it is tightened further.

The tightening bolts should be tightened in a proper sequence as stated in the manual. Simultaneously keep

measuring the distance between pressure plate and back plate, on all four sides for even tightening. Keep

carrying bar and tightening bolts clean and lubricated (not painted). The rollers in the pressure plate and the

connecting plate should be lubricated with lubricating oil. The ball bearings in the roller holders and

tightening nuts should be greased with ball bearing grease.

Gasket Replacement

1. Pull out the old gasket from the groove.

2. If necessary, heat the back of the gasket groove with a hot-air blower.

3. Do not use acetylene gas for heating.

4. Charred or loose cement and rubber remains should be removed by means of a rotating stainless steel

brush.

5. Clean the gasket groove with a clean cloth, dipped in a solvent (acetone, methyl ketone,

trichloretnyleite, etc).

6. The gaskets should be dried with a clean cloth, slightly moistened with a solvent.

7. Gaskets may sometimes be slightly short or long. Short gaskets should be stretched before being

placed in the groove. Long gaskets should first be fitted in the grooves at the plate ends and the gasket

is then pushed into the groove towards the middle

Two basic types of adhesives used for repairs are:

1. Two-components, cold-curing epoxy cement, which gives a strong joint for high temperatures.

Removal of gaskets usually requires heating of the joint.

2. One-component, rubber-based cement with limited temperature resistance. Removal of the gasket

can usually be carried out without heating of the cement joint.

In each case the detailed instructions provided should be strictly followed.

Exchange of Plates

A faulty plate can easily be removed and replaced by a spare plate. Check that the spare plate has holes and

gaskets arranged in the same way as on the removed plate.

If a 4-port plate leaks and no spare plate is available, the leaking plate and the adjoining 4-port plate can be

removed from the plate pack. The capacity of the plate heat exchanger is then reduced, but usually only

slightly. The heat exchanger must be tightened to a correspondingly shorter plate pack length.

FINDING A FAULTY PLATE

In general, it is not possible to locate exactly the faulty plate without dismantling the heat exchanger.

Therefore, to identify a faulty plate, heat exchanger needs to be dismantled, each plate to be inspected for

deformation, cracks or holes and for conditions of gasket.

Advantages and Disadvantages of Shell type HE

Advantages

• Less expensive than Plate type HE

• Can be used in systems with higher temperatures and pressures

• Pressure drop across a tube sheet is less

• Tube leaks are easily to locate and plug by pressure testing

• Tubular coolers in refrigeration system can act as receiver also.

• Sacrificial anodes can protect the whole cooling system against corrosion

• Tubular HE is preferred for lubricating oil cooling because of the pressure differential

• Can be made to any size, large or small

• Less complicated in design, thereby makes the maintenance easier by ship's crew

Disadvantages

• Heat transfer efficiency is lower compared to plate type cooler

• Cleaning and maintenance are sometimes difficult since a tube HE requires enough space at one

end to remove the tube nest

• Capacity of tube HE cannot be increased, once made.

• Requires more space in comparison to plate HE for the same capacity

Maintenance Shell type HE

Periodical preventive maintenance ensures trouble free performance of the heat exchanger. Maintaining the

heat exchanger in a clean condition ensures that faults are detected at an early stage.

The fluid flows through the heat exchanger, even though the associated machinery is not running. For

instance, the main engine lube oil is circulated in the system even when the main engine is not running.

Hence, the maintenance of heat exchanger is carried out as per the specified time interval, performance and

not according to the running hours.

Before commencing the maintenance routines, it should be ensured that the heat exchanger is isolated, all

the pipeline valves are secured and a notice is displayed. The recommended maintenance schedule to be

carried out on the heat exchanger at particular time periods is listed below.

Cleaning Techniques Shell type HE

The efficiency of a heat exchanger reduces when dirt, scales, and deposits accumulate inside and outside the

tubes.

Back flushing is a process used to remove the deposits in the inlet region by reversing the fluid flow for a

short period of time. This does not require dismantling of the coolers and can be carried out with less effort

than manual cleaning.

During the manual cleaning of the tubes, the end covers are removed and the brush with long handle is used

to remove the deposits. In chemical cleaning, chemicals recommended by maker are added to the freshwater

and circulated through the shell or tubes. After a stipulated time, the shell side or tube side is rinsed with

freshwater.

The tube outer surfaces in lube oil cooler or heavy oil heater are cleaned by circulating degreasing solution

recommended by maker. Alternatively, the heat exchanger is dismantled and the tube stack is immersed in

a tank of cleaning solution.

Advantages and Disadvantages of Plate HE

The plate coolers are advantageous except for its cost. Nowadays, the expensive titanium plates in plate

coolers are replaced by stainless steel and aluminium brass.

Advantages

• They are smaller and lighter.

• No extra space is needed for overhaul.

• Plates can be added in pairs to increase capacity.

• Cleaning and maintenance is relatively simple.

• Turbulent flow reduces fouling.

• There is no limit to flow velocity.

• Each plate and the design of the gasket prevent the mixing of two liquids.

• The plates are available in different versions of trough geometry.

Disadvantages

• Any leaks in the plates due to cracks are difficult to locate.

• Joints can deteriorate and may fail due to brittleness.

• Plates, made of titanium are expensive.

• Over tightening can cause permanent damage to the plates.

• Gasketed plate heat exchangers cannot be used for high pressure applications

• Have pressure and temperature limitation of 20 bars and 200 Deg C.

Maintenance Plate HE

The efficiency of plate heat exchanger drops due to fouling of plates. Even though, the corrugations in plates

help to keep the surface of plates clean, some fine debris will deposit.

Periodical preventive maintenance ensures trouble free performance of the heat exchanger. Maintaining the

heat exchanger in a clean condition ensures that faults are detected at an early stage.

Before commencing the maintenance routines, isolate the heat exchanger and ensure all pipeline valves are

secured and a notice displayed.

The following table shows the recommended maintenance schedule for a plate heat exchanger at particular

time periods.

Cleaning Techniques Plate HE

The deposits on the seawater side of the plates are slightly more. In this method, the flow direction of the

seawater is changed. The dirt accumulated in the inlet region and the heat exchanging channels is flushed

out the same way as it entered.

In mechanical cleaning, the plate heat exchanger is dismantled and plate surfaces are cleaned using brushes.

Care should be taken so that packing between the plates are not damaged.

Cleaning of plates can be done in place by sliding the end cover and the plates on their guide bars. While

assembling, the clamping bolts should be tightened to the prescribed torque. The distance between the end

cover plate should be the same as it was before dismantling. Chemical cleaning of the plate surfaces can also

be carried out by circulating the chemical solution recommended by the maker. The cooler plates are made

of titanium, which are highly corrosion resistant.

CHAPTER-3

AIR COMPRESSORS

Introduction

On board the ships compressed air is used for a variety of uses as given below

➢ For automation and control of main and Auxiliary machinery and equipment.

➢ For starting of the main engines, auxiliary engines, emergency generator engine etc.

➢ For pressurizing the hydrophores for domestic fresh water and sanitary water used in

accommodation.

➢ For use in the sewage plant for conducting aerobic sewage breakdowns.

➢ For soot blowing of the boilers.

➢ For use in fog horns and ships whistles.

➢ For heaving the life boat up by the use of an air motor.

➢ Used in pneumatic pumps for oil transfer and pneumatically driven hand tools such as grinder /

chisels / drills/ spanners /jacks etc

➢ For use as general service air for use in general cleaning & painting operations.

Generally, two pressures of air are used: High Pressure --30 bar used for starting the Main/Aux. engines and

Low Pressure -- 7 bar used for control and general service air. For high pressure, reciprocating air

compressors are used. Even in reciprocating Compressors, a compression ratio of 1:7 is common (more than

this the air getting compressed becomes very hot and will reduce the overall efficiency). Hence compression

is done in a two stage with inter / after cooling arrangements.

Onboard the ship, mostly the reciprocating compressors are used, which supplies compressed air. The

compressed air is stored in air receiver. Since compressed air is used for starting main propulsion engine,

auxiliary engine and control systems, it is imperative that the compressor is maintained in a good condition.

Before carrying out any maintenance routine, the makers instruction manual should be studied and

thoroughly understood.

Operating Procedure of a Reciprocating Compressor

The operating manual of the particular machine and the SMS manual would give the specific items to be

checked. However, as a guideline the following to be done.

1. A compressor may be started with the unloaders open after the following checks have been done

2. Check the oil level in the sump and in the lubricator tank.

3. Check that the air intake filter is clean.

4. Check that the cooling water pressure is correct and all the valves in the line must be open.

5. If relief valves can be manually checked using the hand testing levers

6. Pressure gauge cocks: the cocks must be slightly open to avoid excessive pressure fluctuations which

can damage the pressure gauges.

7. Then the compressor can be turned a few revolutions with a turning bar to check for the free

movement.

The compressor can be operated in manual or automatic mode. In manual mode, the delivery valves, cooling

water valves, and drain valves are operated as required before starting. In automatic mode, the valves are

normally kept open. The compressors will cut-in and cut-off automatically depending on the consumption

of the compressed air.

The compressor is started in unloaded condition and loaded during operation. The compressor is unloaded

before stopping. If automatic unloader is not provided, open the drains to unload the compressor and close

the drain valves to load the compressor.

When air is compressed and cooled, the water vapour present in air condenses. The condensed water should

be drained periodically during operation to avoid carry over of the water into the compressor cylinders.

The procedures for starting and stopping the compressor should be followed sincerely. After starting the

compressor, the parameters should be monitored in order to ensure the compressor runs trouble free

Relief valves are provided in between the stages. It releases the excess pressure when the pressure increases

above the set limit. Bursting disc is fitted in the water space of the intercooler. If the cooler tubes fail, it will

burst at a predetermined safe pressure and release the excess pressure.

Fusible plug is fitted on the air receiver. In the event of a fire in the vicinity of air receivers, the increase in

the temperature will cause the core to melt and release the air.

Safe Isolation of the System

➢ Stopped the compressor

➢ Control room circuit breaker put off

➢ Electrical isolation permit should be obtained and Local electrical panel

➢ circuit breaker put off

➢ Shut off the cooling water as appropriate

➢ Shut off the high-pressure discharge line

➢ Remove the compressor from auto start and from priority

➢ Display 'man at work' warning board.

Filter Cleaning and Oil Replacement

The various filters should be opened and cleaned periodically to clear collected sediments and debris. This

ensures smooth flow of the fluids past all stationary and running surfaces including bearings, valves, bores

and cooling passages. Clogged or choked filters will result in drop in pressure or carry over of dirt particles

which eventually could damage the bearings or the machinery.

The lubricating oil system in a compressor has two filters. They are suction strainer and discharge fine filter.

Suction strainer is a screen type filter. If the lubricating oil pressure falls, the filter should be cleaned.

Remove the strainer. Clean the same with super kerosene oil. Blow off with compressed air. Assemble the

same.

The discharge fine filter is available as a “use and throw” cartridge. Replace the same.

Oil Replacement

Oil replacement is carried out every 1000 hours. The crankcase oil is replenished with fresh charge.

Crankcase inspection must be carried out. During crankcase examination in-situ, it is difficult to assess

condition of liner with respect to wear by visual examination. Only, part of the liner, can be felt for any

scouring marks or ridge. Connecting rod play also checked during oil change.

Procedure

➢ Carry out the isolation of the compressor as mentioned above.

➢ Remove the drain plug and collect the oil.

➢ Do not throw the oil, but check the oil for cleanliness, debris and metal particles if any. If so,

investigate the cause and rectify the defect.

➢ Use super kerosene oil to rinse and flush the system. Mop them dry with a clean cotton cloth. Do not

use rags or do not use cloth with fluff.

➢ Flush the system again with the oil prescribed by the manufacturer.

➢ Fit the drain plug. Do not over tighten the plug.

➢ Fill the oil up to the mark.

Air Filter

➢ Air filter is cleaned once in two hundred and fifty hours.

➢ Isolate the compressor as said before.

➢ Use a screw driver to remove the clips.

➢ Remove the suction filter element.

➢ Filters are either of the dry type or wet viscous impingement type. Dry type – is mostly disposable

& wet type: can be chemically cleaned and rinsed with fresh water, etc.

➢ Blow off air, if required replace the filter element.

Overhaul of Compressor Parts

Routine Maintenance of Reciprocating Compressors: A compressor requires a proper planned routine

maintenance for safe and efficient operation and to avoid breakdown maintenance. Routine for maintenance

depends on the manufacturer’s advice given in the SMS manual. The following may be are the maintenance

checks that should be carried out after the mentioned running hours. the following may be taken as guideline.

Precautions Before Overhauling: Air compressor may be overhauled for planned maintenance or stripping

down for survey purposes. First of all, make sure the spare parts are available on board. This will include

joints, gaskets, major spare parts such as piston, piston rings, bearings, etc.

Unless the compressor has suffered a major failure, it would be better to leave overhauling air compressor

until the vessel has berthed, especially on a reversible engine with fixed pitch propeller requiring large

amount of air for manoeuvring.

For survey purpose, ensure the following papers are readily accessible: copies of previous survey reports,

running hours since last survey, copies of planned maintenance reports, recorded clearances and

manufacturer’s recommended tolerances.

Overhauling Air Compressor: The compressor to be isolated both electrically and mechanically and locked

out. ‘WORK IN PROGRESS’ notices are posted. The oil is drained,

Removal of Compressor from Motor coupling

➢ Disconnect the lead connections from the junction box & earth lead connection.

➢ Before dismantling the unit from the carriage, make sure that the pipe lines are free from compressed

air.

➢ Open the safety valves manually and open the drain cocks on the inter cooler and after cooler to

release compressed air if any.

➢ The pipe fittings and then the air filter without spilling the oil.

➢ Remove the compressor unit by opening the foundation bolts. Use hydraulic trolley to remove

compressor unit.

➢ Clean the unit externally.

250hrs: Dismantle and swap all rubber seals and gaskets.

➢ Clean air filter at 250 running hours. It is very important to filter the contaminants in the engine room

atmosphere to reduce abrasions on the liner surface. Also a dirty air inlet filter can raise the delivery

temperature of the air to a dangerous level may be above the lubricating oil flash point and near the

auto ignition point, can cause an explosion.

➢ Clean and inspect valves at 250 running hours. The valves can be damaged due to the ingress of

foreign particles. Excessive lubrication also has been known to damage the valves. The valves should

be removed, inspected, and overhauled at regular intervals. A broken valve part can fall onto the

compression space and cause extensive damages.

➢ Check drive belts at 250 running hours. A v-belt is generally used to drive the cooling water pump.

The tightness of the belt should be checked and adjusted to the correct value at proper intervals. In

addition, a belt dressing spray would protect the belts as well as increase the transmission of the

power and reduce the slippage.

➢ Check unloader operation at 250 running hours. At a regular interval the operation of the unloaders

should be checked and if not satisfactory should be investigated and corrected.

500hrs: Change crankcase oil at 500 running hours. Lubricating oil can lose its property over a period of

time due to the onerous operating conditions. However, the synthetic lubricating oils can be used for a longer

period.

➢ Change lube oil and clean sump.

➢ Clean lube oil filter.

➢ Check and renew suction and discharge valves with overhauled one.

1000 hrs:

➢ Crankcase inspection, main and big end bearing inspection.

➢ Relief valve overhauling

4000 hrs:

➢ Piston and big end bearing overhauling, piston ring renewal .

➢ Intercooler cleaning.

➢ Motor overhauling.

Compressor is stripped down removing cylinder head and valves, piston and connecting rod. The circlips,

gudgeon pin and top end bearing are removed from the piston using proper tools. The piston rings are

removed. The parts are gauged (ring grooves, piston pin diameter, bearing clearances) bumping clearances

checked and the readings are recorded. Safety devices are checked. Hydraulic tester can be used to test the

opening pressure of relief valves.

The parts to be cleaned for survey. Please Note: no evidence of wear or damage is removed.

Dismantling Cylinder Heads

➢ Remove the nuts fixing the cylinder head to the cylinder.

➢ Use a mallet and tap the sides of the cylinder head and take it out.

➢ Decarbonizes and clean it thoroughly.

➢ Examine cylinder head for any damage.

➢ Use new gasket and spring washers below the nuts.

Suction and Delivery Valves

➢ Inspect all the parts for pitting, wear and distortion.

➢ Ensure that the locating pin is not worn out or bent or loose in vent seat.

➢ Renew the valve plates and spring plates in order to avoid fracture due to fatigue.

➢ Never use reconditioned valve plates.

➢ Valve seats should be reconditioned only by skilled personnel since air tightness.

➢ If valve seat, seating face is damaged it should be replaced.

➢ Fit the spring plates properly on the locating pin.

➢ Tighten castle nuts with correct torque and provide split pins

Cylinders

➢ Remove the nuts fixing the cylinder to the crankcase.

➢ Check clearance between the piston and liner bore at right angles at three places, viz. at the top of

the liner, middle of the liner and at the bottom of the liner.

➢ Measure the dimension of the piston at the skirt at to the gudgeon pin bore.

➢ Check the dimensions of the HP cylinder. Replace it with a new one if damaged or worn out beyond

limits.

Connecting Rods

➢ Remove the nuts fixing the side cover to the crankcase and remove the split pins from the connecting

rod bolts and unscrew the nuts.

➢ Take out the connecting rod bolts. Use a mallet and lightly knock out the connecting rod cap.

➢ Take out the connecting rods through the crankcase opening for the cylinder.

➢ Provide new big end bearings and small end bush.

➢ When changing the bearings, ensure that oil holes are properly located and fully opened.

➢ Check for correct fit on the crankshaft.

Motor Mounting Bracket

➢ Unscrew the nuts fixing the motor mounting bracket to crankcase.

➢ Tilt & seat the oil pump fixing face of the crankcase on the floor.

➢ Unscrew the oil seal housing Allen screws and remove the oil seal housing and oil seal.

➢ Take out the motor mounting bracket and then the

➢ Crankshaft from the crankcase.

Piston & Piston Rings

➢ Assemble the rings in their respective grooves and measure the side clearance using a feeler gauge.

If it exceeds the specified limit, replace with a new set for each piston.

➢ Before assembling the piston into cylinder, ensure that the gaps of adjacent rings are in opposite

direction. It controls oil leak and prevents compressed air leak to increase the efficiency of the

compressor

➢ Clean the piston and the ring grooves thoroughly, after de-carbonizing it.

➢ Examine the gudgeon pin for damages.

➢ Insert the ring into the respective cylinder in such a way that it is in level with the top surface and

then measure the butt clearance using a feeler gauge. If it exceeds the specified limits, provide new

rings using proper tools.

➢ Knock out the gudgeon pin from the piston.

➢ Never forget to lubricate the rings before assembling.

➢ Replace small end bearing bush if piston is shaking on connecting rod.

➢ Take out the rings using a piston ring expander.

➢ The gudgeon pin should be push fit in the connecting rod bore.

➢ The piston should be assembled to the connecting rod and check for correct fit.

➢ The side marked TOP on the rings should face the top side of the piston.

Main Journal Bearings

➢ Check the bore size of the bearings and provide new bearing if it is worn out or exceeds the

condemning limit.

Crankshaft

➢ Blow compressed air through the oil holes of the crankshaft and ensure that they are free from any

dirt and blockage.

➢ The balance weights should not be removed from the shaft since reassembling may cause unbalance.

Oil Pump

➢ Dismantle the oil pump, clean it thoroughly and inspect all the parts.

➢ Replace all worn out or damaged parts.

➢ There should not be any end play for the rotors.

➢ There should be sufficient clearance between the rotors and the cover plate so that the rotors do not

stick to the end cover.

➢ If there is excess of end play it can be corrected by lapping the outer face of the pump body.

➢ Ensure free movement of the inner rotor in the outer rotor.

Main Journal Bearings

➢ Check the bore size of the bearings and provide new bearing if it is worn out or exceeds the

condemning limit.

Crankshaft

➢ Blow compressed air through the oil holes of the crankshaft and ensure that they are free from any

dirt and blockage.

➢ The balance weights should not be removed from the shaft since reassembling may cause unbalance.

Oil Pump

➢ Dismantle the oil pump, clean it thoroughly and inspect all the parts.

➢ Replace all worn out or damaged parts.

➢ There should not be any end play for the rotors.

➢ There should be sufficient clearance between the rotors and the cover plate so that the rotors do not

stick to the end cover.

➢ If there is excess of end play it can be corrected by lapping the outer face of the pump body.

➢ Ensure free movement of the inner rotor in the outer rotor.

Air Compressor Assembly

Major parts such as piston, bearings, etc. to be inspected and renewed if necessary. Piston rings would also

be renewed as would the gudgeon pin and top end bearing. Before fitting new piston rings, butt and axial

clearances to be checked. Ensure correct tool is used to guide the rings to the cylinder bore. Checking

bumping clearance is necessary after a major overhaul. Normal value of bumping clearance for a two stage

main air compressor is about 0.5 mm. Use modern ‘squeezable plastic’ or ‘lead wire ball’ for measuring

bumping clearance. After fitting cylinder cover, turn flywheel by hand to make sure it is free to turn.

All nuts to be torque tightened to correct settings and with new locking devices such as split pins. Suction

and discharge valves must be renewed or overhauled.

Clean or renew crankcase oil suction filter and refill crankcase with new oil. Renew lube oil filters and air

filter. Open cooling water valves and check for leakages. Turn the flywheel continuously by hand to prime

the lube oil pump. Conduct an initial running of compressor in unloaded condition and check motor amperes,

noise, etc. Then load the compressor and then check for bearing overheating. Once everything found

satisfactory, test run the compressor and measure time taken to fill the air bottle from empty to full.

Keep all the records of clearances, spare parts consumed, etc. and sent to the company. Raise requisitions

for necessary spares immediately. Update the work done and running hour in computer based planned

maintenance system (PMS).

Overhaul of Cylinder head

The isolation of cylinder head should be carried out. Cylinder head accommodates mountings such as LP,

HP suction and delivery valves, air suction filter.

The cylinder head is connected to cooling water connection, high pressure air delivery pipe and suction filter.

All the paraphernalia connections should be removed.

Cylinder head is held to the top surface of the cylinder, by nuts which are torque tight.

Use the tool provided by the manufacturer to slacken the same. Remove the nuts. Use correct lifting tool to

lift the cylinder head clear form the top face of the liner.

Bumping Clearance

The bumping clearance is the clearance between the piston and the cylinder cover when the piston is at the

top of its stroke. It is normally between 0.5 and 1% of the cylinder bore. The effect on the volumetric

efficiency due to different bumping clearances is shown below.

➢ The clearance is measured by removing the valves, inserting lead wire under the cylinder cover.

➢ The lead wire must be at the centre of the piston and the flywheel is turned by hand.

➢ Remove the lead wire and measure the thickness of lead wire.

➢ This will give the bumping clearance. Compare this with the maker's manual.

➢ Adjustment of the clearance varies between different types of machines.

➢ Adjustment is usually by addition or removal of shims or joints. The thickness between the head and

the block can be adjusted or shims between the connecting rod big end halves can be added or

removed.

➢ With tandem type pistons it is necessary to be able to adjust each stage independently

➢ Causes of higher bumping clearance: Bearing wear down causes the bumping clearance to

increase. This means that less air is drawn into the cylinder and so the efficiency of the compressor

will decrease.

➢ Causes of lesser bumping clearance: If bumping clearance is less, piston is likely to touch the

underside of the cylinder.

➢ The reason where piston is likely to touch the underside of the cylinder , is :- (a). Excessive clearance

at crankpin bearing/ main journal bearing. (b). when unit is unloaded – with these two faults , during

the upward stroke of the piston , there is a vertical uplift of the piston and with no air cushion, all

likelihood of the piston banging on the cylinder.

➢ Precautions - It is better to make one or two attempts to get a reading. Excess lead wire will strain

the cylinder cover studs and the piston.

Overhaul of LP and HP valves are carried out according to the maintenance prescribed by manufacturer.

Accordingly, every mounting is removed from the cylinder with respective special tool and overhauled. The

above said components are assembled back to the cylinder head. The cylinder head is pressure tested.

The cylinder head gasket is replaced and the head is tightened using torque spanner in correct sequence. The

tightening torque values are mentioned in the manual.

Overhaul of valves

LP stage valves are separate valves such as suction and discharge. While some manufacturers adopt

combination valve i.e. combined suction and delivery valve for LP stage HP suction and delivery stage

separate valves

Valves Overhaul Procedure

The compressor must first be electrically isolated with the fuses removed and an electrical isolation and work

permit granted by the chief engineer.

Thereafter the first stage and the second stage suction and discharge valves should be removed and brought

to the workshop for overhauling.

Marine compressors use the Plate type automatic valves. The suction and the discharge valves look similar;

however, the direction of the operation and the spring stiffness differs. The suction valve springs are of lower

spring stiffness than the discharge ones and they must never be mixed up. Also when using new spare parts

the part number must be carefully checked from the operation and maintenance manual to avoid mixing them

up.

When opened up the suction valves are found to be in clean condition while the discharge valves would have

some degree of carbonization. In case a valve is opened up and some parts are found to be broken, all the

broken parts must be located to avoid any further damage to the machine. An exploded view of the

compressor valve has been shown and the overhaul procedure is as follows:

➢ Remove the split pin and open the castle nut.

➢ Dismantle all the parts and soak in kerosene or clean diesel oil.

➢ Clean all the parts with a soft brush. In case of a hard deposit a copper plate of washer can be used

for the scraping action.

➢ Check the valve plates and the valve seats for any damage and cracks. If any signs of fatigue cracks

on the valve plates are present, then the

➢ valve plate must be replaced with new ones. The valve plate must never be turned over and used as

it can lead to fatigue failure.

➢ The valve plate and the valve seat must be separately lapped on a surface plate using fine and extra

fine grinding paste.

➢ Thereafter all the parts must be washed with diesel and cleaned with compressed air.

➢ The valve should then be assembled, with the lapped surface of the valve plate and the valve seat

facing each other.

➢ After the assembly of the valve the operation of the valve should be checked by a soft wooden stick.

After the overhaul the valves have to be checked for leakage. The space above the valve plate should be

filled up with water or light oil like kerosene. If after a few minutes no drop in level or leakage is there then

the valve is satisfactory for the use. While installing care should be taken to avoid the interchange of the

suction and the discharge valves, as it could lead to an explosion due to over pressurization of the

compression chamber.

Safety Devices

Safety Features of Marine Compressors

Marine compressors have various safety features and cut-outs installed so that they will trip when running

in an unsafe mode.

Relief valve: Normally fitted between 1st stage and inter cooler and 2nd stage – after cooler to release excess

pressure developed inside it. The setting of the lifting pressure increases after every ascending stage.

Bursting disc: is a copper disc provided at the air cooler—both inter / after cooler of the compressor. It is a

safety disc which bursts when the pressure exceeds over the pre-determined value due to leaky air tubes of

the cooler.

Fusible plug: Generally located on the discharge side of the compressor, it fuses if the air temperature is

higher than the operational temperature.

Lube Oil low pressure alarm and trip: If the lube oil pressure goes lower than the normal, the alarm is

sounded followed by a cut-out trip signal to avoid damage to bearings and crank shaft.

Water high temperature trip: If the intercoolers are choked or the flow of water is less, then the air

compressor will get over heated. To avoid this high water temperature trip is activated which cut offs the

compressor.

Water no-flow trip: If the attached water pump is not working due to some mechanical failure, or the

intercooler is chocked restricting the cooling water flow, not enough to cool the compressor, then moving

parts inside the compressor will get seized due to overheating. A no flow trip switch is provided to trip the

compressor.

Motor Overload trip: If unloader is not in open position, when the compressor is started, then starting

current becomes too high which can damage the Motor or while running due to some mechanical issue, like

main bearing seizure, broken piston rings etc, the current can be high. Hence an overload trip is provided

The safety devices usually fitted to an air compressor are:

➢ Relief valve fitted to every stage

➢ Fusible plug (melts at 120 c)

➢ Bursting disc for cooling jacket

➢ Alarms and cut outs for air compressor are:

➢ High air temperature

➢ High cooling temperature

➢ Low lubricating oil pressure

Compressor intercooler

Bursting disc

The bursting disc is an important safety device provided for cooling jacket and inter cooler so that in the

event of failure of the air cooler or air leaking in to cooling water jacket, bursting disc will blow out and

excess pressure is relieved. If this excess pressure is not relieved, the cast iron casing of the compressor will

be damaged. In common bursting disc is made from copper sheet and designed to burst at a predetermined

safe pressure, therefore preventing any damage to compressor casing and personnel. If at any time bursting

disc to be renewed, it must only be replaced with same material and thickness as per maker's specifications.

Maintenance:

➢ Slacken the spindle fully.

➢ Inspect the disc.

➢ Clean the dirt accumulation in the space.

➢ Remove and replace the o-ring after cleaning the o-ring seating area.

➢ Reset to lift at 10% in excess of max. working pressure.

Troubleshooting of Air Compressor

Though the problems encountered onboard differ from ship to ship, a brief guideline is given regarding the

causes of the different symptoms.

1. Lube oil pressure low: causes can be leakage in pipes, suction strainer choked, oil grade wrong, gear

pump faulty, faulty pressure gauge, increased clearances of the bearings, and oil level low.

2. Cooling water high temperature: causes can be cooling water valves closed, cooling water piping

blocked, cooling water pump belt lose or broken, cooling water pump faulty, no flow of cooling water,

and low level of cooling water in the expansion tank.

3. Compressor noisy: causes can be bearings worn, crankshaft end play high, discharge pressure high,

poor foundation, small bumping clearance, piston rings worn, liner worn out causing piston slap,

valves not properly seated, and valves broken or faulty.

4. First stage discharge pressure low: causes can be that the first stage suction valve is not closing fully

and allowing the air to leak during the compression or it is not opening fully allowing less air to come

in the chamber or the discharge valve is faulty and opening prematurely or incorrect springs have been

fitted which are compressing on little pressure, intake filter fouled, leakage from piston rings.

5. First stage discharge pressure high: causes can be that the second stage suction valve is not holding

and while compression high pressure air is coming to the inter-cooler and showing an increase in the

pressure, inter-cooler tubes choked.

6. Second stage discharge pressure low: causes can be leakage from the piston rings, second stage

suction valve faulty and allowing the air to escape, second stage discharge valve leaking or opening

prematurely due to wrong springs fitted.

7. Second stage discharge pressure high: causes can be obstruction in the after cooler, obstruction in the

discharge valve, air bottle pressure high, second stage discharge valve springs very stiff.

8. Unloader in Compressors

All compressors need to be unloaded during starting/ stopping and at regular intervals due to

➢ Restriction of Starting Current in the motor, start with unloader open and then close unloader

➢ Compressor draws air from the engine room atmosphere, where air is not dry and is mixed with

moisture and oil. This air when compressed, the volume of air comes down and the oily moisture

mixture can damage the compressor parts like, piston, valves etc. Hence should be drained at

regular intervals—Use of unloader drains this mixture of oil /Moisture.

➢ At stopping the same is done so as to drain all the moisture inside and in preparation for the next

starting.

➢ Intermittently the compressor is unloaded to remove the condensed water inside which could go

outside with the air.

➢ Pneumatic and solenoid operated unloaders are quite common. A built in timer circuit energises

the solenoid valve during starting /stopping and opening the unloader intermittently is also done by

the timer circuit.

Air Receiver

Air receiver stores the compressed air supplied by the compressor. Classification societies state that there

must be sufficient capacity for a minimum number of 12 consecutive starts for main engine, in both ahead

and astern direction.

At least two receivers of approximately the same size are to be provided. Main air receivers are classified

as unfired pressure vessels and are constructed accordingly.

Construction is from mild steel boiler plate with UTS of between 420 and . With an elongation of not less

than 20%, cylindrical section may be rolled from one or two plates and joined by longitudinal welded seams.

The ends are dished and welded to the cylindrical shell with one end having a manhole opening to take an

elliptical door.

After construction, the receiver has to be stress relieved by heating, slowly to a temperature of 580 to , and

held at the temperature for one hour per 25mm thickness. The minimum time for heating one hour. Then it

is allowed to cool slowly and uniformly down to, and then to cool in still air to ambient temperature.

Manhole door - This opening is provided for man entry.

Name Plate - Details of the bottle maximum pressure and working pressure together with the manufacture's

name written on this.

M/E start valve - This is the main stop valve on the air reservoir which supplies air to the main engine for

purpose of starting.

A/E start valve - This is the main stop valve on the air reservoir which supplies air to the Auxiliary engine

for purpose of starting.

Safety valve - Being a pressure vessel, a safety valve is mandatory. This is provided to relieve the air bottle

of air pressure in excess of the safe working limits.

Control air valve to reducing station - This is the main stop valve on the air reservoir which supplies air

to the control air and automation equipment.

Service air valve to reducing station - This is the main stop valve on the air reservoir which supplies air

to all the services within and outside the engine room. On some ships this valve may lead the air to a seperate

air bottle of 7 bars capacity storage from where it is used further.

Soot blow valve - Certain boilers may have soot blowing arrangements within high pressure air. This is the

main stop valve on the air reservoir which supplies air to the soot blowers.

Whistle air valve to reducing station - This valve opens air to operate the ships horn.

Filling valve - This is a non-return valve. Air from the discharge of the air compressors is led through this

valve into the air bottles.

Note: Usually main air bottle pressure is 30bar; therefore, air supplied from main bottle to different

distributions like control air, service air and whistle air are passed through a reducing valve so as to bring

down the distribution pressure to 7-bar.

Internal Inspection

Before carrying out any inspection the air bottle must be drained and isolated from any possible source of

compressed air, i.e. interconnections to other receivers.

The receiver must be treated as an enclosed space and the check list concerning this must be adhered to.

Inspections are carried out on air receivers to determine if there is any corrosion or cracking. The internal

surface is inspected, particularly in the regions where water collects, for corrosion and coating damage.

Inspections should also be carried out on areas where the coating is damaged due to local pitting. All welds

are inspected for stress cracking including welds around mountings. The normal rules for the fit of the

manhole door apply.

Receiver Inspection

➢ Obtain Permit to work

➢ Treat as enclosed space – personnel outside when internal work is in progress

➢ Drain

➢ Blank all possible means of compressed air entry. There is a manhole door at the end of the air

receiver. It is hinged from the inside with 2 studs.

➢ When the door is in position, the air pressure in the receiver will keep the door shut tight, while the

2 studs are for securing the door in place.

➢ Inspect shell

➢ Inspect fittings and re-coat internally. The internal surfaces are coated with a protective coating such

as clear varnish (copal).

➢ Fit of manhole

➢ Test for leaks.

CHAPTER-4

PUMPS

A pump is a device which imparts energy to a fluid. Onboard the pumps are used for various services, such

as main engine propulsion plant, auxiliary engine power generating plant, auxiliary boiler plant, and cargo

plant, etc. Pump failure can render in shut down of the entire plant. Therefore, correct functioning and

maintenance of pumps and pumping systems is of paramount importance.

Before carrying out any maintenance routine, the maker's manual should be studied and thoroughly

understood. Before moving in to details of maintenance, a class four engineer should be in a position to

understand how a pump looks like.

Maintenance Chart

Maintenance carried out in a pump is enormous, involving minute details. Periodical preventive maintenance

ensures trouble free running of the pump. A good watch on pump running parameters is essential so that

faults are detected at an early stage.

Before commencing any maintenance, isolate power supply, shut the suction and discharge valves. The

planned maintenance schedule is developed based on manufacturer’s recommendations and class

requirements. Every engineer should follow planned maintenance to ensure trouble free operation of the

pumping system.

However, it is the responsibility of the ship owner and staff to periodically review the schedule considering

the operational conditions.

Bearing Puller-Dismantling

Remove the bearing from its seat by using a puller. If possible, let the puller engage the inner ring, then

remove the bearing with a steady force until the bearing bore completely clears the entire length of the

cylindrical seat.

Note: Do not hit with a hammer directly on the bearing.

Safe Isolation of the system

▪ Stopped the pump

▪ Control room circuit breaker put off

▪ Electrical isolation permit should be obtained and Local electrical panel circuit breaker put off

▪ Shut off the suction line as appropriate

▪ Shut off the high-pressure discharge line as appropriate

▪ Check via purge cock that there is no pressure inside the pump

▪ Remove the pump from auto start and from priority

▪ Display 'men at work' warning board.

Overhaul of Centrifugal Pump

Dismantling of Pump:

Never place dismantled parts directly on the floor or on a dirty workbench but always on a clean surface.

Before dismantling, check that the motor cannot be started by isolating the power supply.

Prior to dismantle, make sure suction and discharge valves of the pump is shut. Confirm valves are holding

1. Remove the distant piece, fitted between the pump and motor coupling after removing both motor

and pump side coupling bolts and discs.

2. Remove cooling connections to mechanical seal.

3. Remove casing top cover bolts.

4. Once casing cover bolts are removed, pump assembly is free to remove from place along with shaft

bearing housing, bearing, mechanical seal, impeller and impeller shaft with sleeve.

5. On removing the pump assembly, slacken impeller lock nut and remove the impeller from the shaft

6. Remove shaft key. Care should be taken for not losing the shaft key.

7. Remove distance ring.

8. Slacken the holding screw and remove mechanical seal's rotating part.

9. Slacken bearing housing bolts fitted on casing cover.

10. Remove casing cover from the shaft.

11. Remove shaft sleeve from shaft.

12. Remove bearing housing cover.

13. Remove bearing retaining circlip.

14. Remove bearing housing along with bearing.

Cleaning and Inspection of parts:

1. Remove bearing from housing for inspection.

2. Clean impeller, bearing, shaft sleeve, casing and the shaft. Inspect and evaluate each part for any

damages, deformation, wear and tears.

3. Measure the clearance between impeller and wear rings for top as well as bottom wear rings. If

clearance is more than the maker's recommendation, renew it.

4. Inspect shaft sleeve for any wear down. If sleeve found worn out, renew the same.

5. Check the condition of bearing. If found not good, renew the same.

6. Check the conditions of mechanical seal's rotary and stationary parts. If found damaged, renew it.

7. Check bearing bush at the casing bottom and confirm any wear down. If worn out beyond acceptable

limits, renew it.

Assembling to be done in reverse order of dismantling.

1. Pass the bearing housing through the shaft and then fit the bearing in housing.

2. Fix retaining circlip for bearing and apply required grease for the bearing.

3. Fit the bearing housing cover.

4. Renew the top and bottom O-rings for casing cover.

5. Fix mechanical seal's stationary part with the casing cover.

6. Fit the shaft sleeve.

7. Pass the casing cover through the shaft.

8. Fix mechanical seal's rotary part on the shaft sleeve and tighten the lock screw.

9. Insert distance ring.

10. Fix shaft key and secure impeller.

11. Tighten impeller by shaft nut and lock plate.

12. Now, impeller assembly is ready for lowering in to pump casing.

13. Lower the impeller assembly and tighten the pump cover with volute casing.

14. Tighten the bearing housing with casing top cover.

15. Connect the cooling pipes for mechanical seal.

16. Open liquid to casing, purge the casing and confirm mechanical seal is intact with out any leaks.

17. On confirming pump is free to turn and mechanical seal not leaking, distant piece for connecting

pump and motor coupling, can be fitted with coupling discs.

18. Operate the pump and check the performance, by monitoring its parameters.

Reciprocating Pump

Parts of a Reciprocating Pump

Major Parts of the Reciprocating pump

▪ A piston & Piston rings

▪ Liner

▪ Inlet and outlet valve

▪ Shaft

▪ Relief valve

▪ Piston Rod

▪ Connecting Rod & Crank

▪ Shaft

▪ Prime mover

Working Principle of the reciprocating pump

This pump works in a similar manner as the reciprocating compressor; the piston has the function of

providing the suction force, so that the liquid can be lifted up or sucked in easily. After that comes the

compression part which will impart the required pressure energy to the fluids. In this phase the piston have

to do work so that the liquid can be compressed properly and its pressure can increased to the desired level.

The inlet and the outlet valve open at a certain ‘set’ pressures.

During the suction stroke the piston moves right, thus creating vacuum in the Cylinder. This vacuum causes

the suction valve to open and water enters the Cylinder. During the delivery stroke the piston moves towards

left. The increasing pressure in the cylinder causes the suction valve to close and delivery valve to open and

water is forced to the delivery pipe. The air vessel is used to get an uniform discharge. If the piston is of

single acting type which means it can suck from one side and transmit or deliver to the same side only. But

we can have a double stage pump, which has the function of the creating suction and discharge

simultaneously on either side.

The air vessels in the discharge and the suction line act as a buffers and reduce pressure fluctuations. An air

vessel usually fitted in the discharge pipe dampens the pressure variations during discharge. As the discharge

pressure rises the air is compressed in the vessel, and as the pressure falls the air expands. The peak pressure

energy is thus stored in the air and returned to the system when pressure falls.

This pump can be powered by a Motor or an auxiliary steam engine. The piston, piston rings and liner are

from corrosion resistant materials.

The reciprocating positive displacement pump above, demonstrates the operating principle. The pump is

double acting, that is liquid is admitted to either side of the piston where it is alternatively drawn in and

discharged. As the piston moves upwards, suction takes place below the piston and liquid is drawn in, the

valve arrangement ensuring that the discharge valve cannot open during suction stroke. Above the piston,

liquid is discharged and the suction valve remains closed. As the piston travels down, the operations of

suction and discharge occur now on opposite sides.

A relief valve is always fitted between the pump suction and discharge chambers to protect the pump should

it be operated with a valve closed in the discharge line.

Reciprocating pumps are usually classified as follows:

▪ Direct acting or indirect acting Simplex (single) or duplex (double)

▪ Single acting or double acting

▪ High pressure or low pressure

▪ Vertical or horizontal

Uses of reciprocating pump

There are various uses of the reciprocating pump and they are as following:

▪ The lubricating pump is a reciprocating pump and it supplies the lubrication oil to the main engine.

▪ Main bilge suction pump is also a reciprocating pump.

Advantages

▪ Gives high pressure at outlet.

▪ Gives high suction lift.

▪ Priming is not required in this pump.

Disadvantages

▪ High wear and tear, so requires a lot maintenance.

▪ The flow is not uniform, so we have to fit a bottle at both ends.

▪ The flow is very less and cannot be used for high flow operations.

▪ More heavy and bulky in shape.

▪ Initial cost is much more in this pump.

Vertical Duplex Bilge & Stripping Pumps

Dawson Downie Lamont produce a range of light and heavy-duty Vertical Duplex motor and steam driven

piston pumps for bilge and cargo stripping service. These pumps are carefully designed to give reliable,

efficient service with the minimum of attention.

Design Features

▪ Robust and compact in construction.

▪ They can handle efficiently all grades of oils from petrol to viscous liquids under difficult suction

conditions.

▪ Air vessels are fitted on the discharge side to eliminate pipe line vibration.

▪ Pockets which can collect gas have been avoided.

▪ The valve areas are large and the valve lift has been kept to a minimum to ensure quick reseating.

▪ Large covers and doors on the valve chest to give easy access to valves for inspection.

▪ Flow Rates up to 225 m3/hr. Pressures up to 18 bar.

Maintenance required on the reciprocating pump

Since there are many moving parts, the wear and tear is lot in this pump. There are more operational

maintenance checks on this pump to keep it working and also prolong its life. Reason, why these pumps are

limited in use on board; they are used in places where there is low suction and high-pressure head is required.

The pump below is direct acting because the pump rod is a DIRECT extension of the piston rod; and,

therefore, the piston in the power end is DIRECTLY connected to the plunger in the liquid end. In an indirect-

acting pump, there is some intermediate mechanism between the piston and pump plunger.

The intermediate mechanism may be a lever or a cam. This arrangement can be used to change the relative

length of strokes of piston and plunger or to vary the relative speed between piston and plunger. Or the pump

may use a rotating crankshaft.

In the pump the steam piston is larger in diameter than the plunger in the liquid cylinder. Since the area of

the steam piston is greater than the area of the plunger, the total force exerted by the steam against the steam

piston is utilized on a smaller area of the plunger. Due to this (F= p X Area), the pressure developed is greater

in the liquid cylinder. A high-pressure pump thus discharges a comparatively small volume of liquid against

high pressure or delivery head. Conversely, a low-pressure pump may have a comparatively low discharge

pressure but a larger volume of discharge. In a low-pressure pump, the steam piston could be smaller than

the plunger in the liquid cylinder.

Following are the maintenance carried out on this pump.

▪ The piston rings which are used are always in direct contact with the liner body and hence they wear

a lot. So we have to change them time to time.

▪ The valves used in this pump have to be taken care as it will lead to leakage across them, if they go

bad.

▪ The gland packing from where the shaft comes out of the pump has to be maintained in order to

control any leakage.

▪ In coupling or the cross-head of the pump (where the piston gets the linear motion) also have to

checked for any type of misalignment and wear and tear.

Problems and Possible Causes

Low Volumetric Efficiency (Failure to Deliver Rated Capacity and Pressure)

1. Air or vapor pocket in inlet line

2. Capacity of charge pump less than capacity of power pump

3. Air or vapor trapped in or above inlet manifold

4. Air leak in liquid supply piping system

5. Loose bolts in pump inlet manifold

6. Air or gases entrained in liquid

7. Foreign object holding pump inlet or discharge valve(s) open

8. Incorrect drive ratio

9. Loose belts

10. Incorrect motor or engine speed

11. Loose valve covers or cylinder head

12. Worn valves and seats

13. Safety relief valve partially open, or not holding pressure

14. Worn liners, piston rings or plungers

15. Bypass valve open, or not holding pressure

16. Blown liner gasket

17. NPSH not sufficient

18. Liquid bypassing internally

19. Foreign object blocking liquid passage

20. Vortex in supply tank

21. Insufficient power delivered by motor

NPSH Too Low

1. Inlet line partially clogged

2. Liquid vapor pressure too high

3. Liquid pumping temperature too high

4. Restricted inlet pipe fittings

5. Inlet line too long

6. Too many pipe fittings

7. Too small inlet line

8. Too low static inlet head

9. Too low atmospheric pressure

Liquid Not Delivered

1. Pump not primed

2. Air or vapor pocket in inlet line

3. Clogged inlet line

4. All inlet valves propped open

5. All discharge valves propped open

6. Loose bolts in pump inlet manifold

7. Too high valve velocities

Cavitation

1. NPSH too low

2. Liquid NOT Delivered to Pump Inlet Connection

3. Excessive Stuffing Box Leakage

4. NPSH too high

Leak at Cylinder Head or Valve Cover

1. Over Recommended Pressure

2. Loose Cylinder Head/Valve Cover

3. Damaged Gasket/O-ring

Water in Crankcase/Oil

1. Water Condensation

2. Worn seals

3. Clogged Air Breather(s)

4. Worn Crankcase Packing

5. Loose Covers

Oil Leakage from Crankcase

1. Oil Level/Temperature Too High

2. Worn seals

3. Worn Crankcase Packing

4. Loose Crankcase Cover

Excessive Heat in Power End

1. Pump Running Backward/RPM too low 2) Insufficient Oil in Power End

2. Excessive Oil in Power End

3. Incorrect Oil Viscosity

4. Operating Pump above Recommended Pressure 6) Main Bearings too Tight

5. Drive Misaligned

6. Belts too Tight

7. Pump RPM too Low

8. Inadequate Ventilation

9. Liquid End Packing Adjusted too Tight (adjustable style packing only)

Pump Overloads Driver

1. Pump RPM too High

2. Low Voltage or other Electrical Trouble

3. Trouble with Engine, Turbine, Gear Reducer or other Related Equipment

4. Excessive Discharge Line Pressure

5. Clogged Discharge Line

6. Closed/Throttled Valve in Discharge Line

7. Incorrect Plunger/Piston Size for Application

8. Improper Bypass Conditions

9. Over-tightened Stuffing Box Glands on Adjustable Packing

10. Insufficient Cooling

Stuffing Box Leakage

1. Worn Packing

2. Worn rods or plunger

3. Worn stuffing boxes

4. Wrong size packing

5. Worn O-ring seal (replaceable boxes). Discharge Valve, one or more, Stuck Open

Stud Failure

1. Excessive discharge pressure

2. Improper torqueing of nuts

3. Shock overload caused by pump cavitation

Excessive Valve Noise

1. Broken or weak valve spring

2. Pump cavitation

3. Air leak in inlet piping or loose bolts in pump inlet manifold

4. Air trapped above inlet valve

Inlet or Discharge Line Vibration

1. Piping inadequately supported

2. Inlet line too long or too small in diameter

3. Too many bends in inlet line

4. Multiple pump installations operating in phase

5. Obstruction Under Valve(s)

6. Packing Worn

7. Operating Above Recommended Pressure or RPM

8. Low NPSHA

Noisy Operation (Be sure to differentiate between liquid knock and mechanical knock)

1. Piston or plunger loose

2. Valve noise amplified through power end

3. Pump cavitation

4. Liquid knock

5. Air leak in inlet piping

6. Loose bolts in pump inlet manifold

7. Hydraulic noise in liquid end

8. Loose or worn crosshead pins and bushings

9. Loose connecting rod cap bolt

10. Worn connecting rod bearings

11. Worn crosshead

12. Main bearing end play excessive

13. Worn gears or chains

14. Gears or chains out of line

15. Pump running backward

16. Partial loss of prime

17. Shocks in piping system

18. Water in power end crankcase

19. Poorly supported piping, abrupt turns in piping, piping misaligned, pipe size too small.

GEAR PUMP

Introduction:

The gear pump is a rotary pump, positive displacement type, used for pumping liquids. The pump can be

either horizontally mounted or vertically mounted. The screw pump normally works with two gears. In a

twin gear pump, one is connected to the motor and moves the other gear shaft. The drive and the driven

shafts rotate in the opposite directions. The driven shaft is inside the casing of the pump and is mounted on

bearings / bushings on both ends. The drive shaft, mounted on bearings / bushings, is coupled to the motor

and has normally a mechanical seal to prevent the leakage of liquid. As in any other flange coupled machines,

alignment plays a greater role, in proper running of the machinery. If properly aligned, the gear pump hardly

breaks down.

Preparations for overhaul

Preparations Precautions

▪ Make sure that the necessary spare parts are available - Oil Seal, Bushings/ bearings

▪ Switch of the Power supply to the Motor and remove the fuse.

▪ Shut the outlet and inlet valves from /to the pump

▪ Keep a warning sign indicating that the Motor should not be turned on as the work is in progress

▪ Remove the coupling bolts and the foundation bolts of the motor and slightly push the motor back.

▪ While moving the motor back, please take the shims if any, below the motor under the foundation

bolts – These might have been used for the alignment and keep the shims in the same order for the

reuse.

▪ Remove the flange bolts in both inlet and delivery pipe lines. Make sure to inspect the joints for any

damages after the pump is removed from its foundation.

▪ Remove the foundation bolts, and lift the pump with the inlet and delivery pipelines to the nearest

place where the pump can be dismantled.

▪ When the pump is removed, make sure to take note of the shims if any under the foundation bolts,

used for the alignment and keep them in the same order for the reuse.

▪ Get the foundation place cleaned while the cleaning of the pump parts are done.

▪ Remove the pipelines on the suction and delivery sides from the pump and have the left out oil if any

poured to the tray.

Overhauling the gear pump

Overhaul

▪ Remove the drain plug of the pump and drain the oil to the tray

▪ Remove the bolts on the back cover of the pump and carefully take out the back cover.

▪ (Most manufacturers provide thread holes in the back cover on left and right side, for using the correct

bolt and tighten the bolts equally - the bolts pushes the gear pump outer shell and loosens the grip,

assisting the back cover get released)

▪ Please remember that both the drive and driven shafts moves on two bushings each One bush for

each of the shaft sit in its place on the back cover.

▪ Similarly two more bushings (one for the drive and the other for the driven) locate in the front side

of the shell.

▪ Once the back cover is removed, the driven or idler shaft can be easily removed from both the

bushings. Similarly remove the drive shaft and the gear - if mounted on the drive shaft with the key.

▪ Please note--Some manufacturers make the gear integral with the shaft

▪ Once all the parts are removed, it should be properly cleaned

In a gear shaft, three important things to be done

Check the back-lash clearance: if this is more than the permissible limit as given in the manual, the gears

need to be changed. Please record the backlash clearances for future reference

Check the bushings / bearings (many manufacturers use ball bearings instead of bushings in high capacity

pumps there by reducing the frictional losses) If they are worn out or the ball bearings produce a crude noise,

when turned with the hands, then they need to be changed

Check the oil seal, if lips are worn or slightly damaged, it has to be renewed.

If the overhauls is for the PMS or condition based monitoring program, it is better to change the oil seal—

in our view, it is always good to change the oil seal whenever the pump is dismantled.

Clean the joint sitting places on both the main shell and back cover correctly if the joints are damaged, should

be replaced

Once completed, the gears have to be assembled and boxed up, make sure to hold the back cover correctly

and in place while the gear shafts enter the bushings/ bearings.

Make sure to turn the drive shaft with hand and should turn with out any wobbling

The back cover is tightened properly with the new joint. The drain plug is put in place

The inlet and the outlet pipe lines are fitted to the pump with the proper thread seals. With this the basic gear

pump overhaul is completed.

But the pump is to be placed in the cleaned foundation, with the correct shims in place. Then move the motor

in such a way that both the flanges are close to each other—remember to keep the shims if any under the

motor also correctly. Please check if there is any glaring misalignment.

SCREW PUMP

Introduction

The screw pump is a rotary positive displacement type, used for pumping liquids. The pump can be either

horizontally mounted or vertically mounted.

Screw pump is always provided with a relief valve, which will bypass the liquid back to the suction side.

The screw pump normally works with two or three screws. In a twin screw pump, one is connected to the

motor and moves the other screw shaft using a timing gear. The drive and the driven shafts rotate in the

opposite directions. The driven shaft is inside the casing of the pump and is mounted on bearings on both

ends. The drive shaft, mounted on bearings, is coupled to the motor and has normally a mechanical seal to

prevent the leakage of liquid. As in any other flange coupled machines, alignment plays a greater role, in

proper running of the machinery. If properly aligned, the screw pump hardly breaks down.

Preparations for o-haul

Precautions

1. Make sure that the necessary spare parts are available—Oil Seal, Bushings/ bearings

2. Switch off the Power supply to the Motor and remove the fuse.

3. Shut the outlet and inlet valves from /to the pump

4. Keep a warning sign indicating that the Motor should not be turned on as the work is in progress

5. Remove the coupling bolts and the foundation bolts of the motor and slightly push the motor back.

6. While moving the motor back, please take the shims if any, below the motor under the foundation

bolts These might have been used for the alignment and keep the shims in the same order for the

reuse

7. Remove the flange bolts in both inlet and delivery pipe lines. Make sure to inspect the joints for any

damages after the pump is removed from its foundation

8. Remove the foundation bolts, and lift the pump with the inlet and delivery pipelines to the nearest

place where the pump can be dismantled.

9. When the pump is removed, make sure to take note of the shims if any under the foundation bolts,

used for the alignment and keep them in the same order for the reuse

10. Get the foundation place cleaned while the cleaning of the pump parts are done

11. Remove the pipelines on the suction and delivery sides from the pump and have the left out oil if any

poured to the tray hardly breaks down.

Overhauling the screw pump

▪ Remove the drain plug of the pump and drain the oil to the tray

▪ Remove the bolts on the back cover of the pump and carefully take out the back cover.

▪ Most manufacturers provide thread holes in the back cover on left and right side, for using the correct

bolt and tighten the bolts equally the bolts pushes the gear pump outer shell and loosens the grip,

assisting the back cover get released

▪ Once the back cover is removed, you will see the pump as shown in the below

Please remember that both the drive and driven shafts moves on two bearings each; Two more bearings (one

for the drive and the other for the driven) located in the front side of the shell. One pair each for the drive

and the driven shaft.

Once the back cover is removed, the driven or idler shaft can be easily removed from both the bushings.

Similarly remove the drive shaft and the gear if mounted on the drive shaft with the key.

Please note-Some manufacturers make the timing gear also integral with the shaft like the screws. Once all

the parts are removed, it should be properly cleaned.

In both drive and driven shafts, Check the backlash clearance for the timing gears: if this is more than the

permissible limit as given in the manual, the gears need to be changed. Please record the backlash clearances

for future reference

BACKLASH

Using a dial indicator, to measure the backlash

Using a feeler gauge for backlash measurement (for smaller pumps)

Standard gear backlash: 0.02 to 0.15 mm (0.0008 to 0.0060 in.)

Maximum gear backlash: 0.20 mm (0.0079 in.)

If the gear backlash is greater than the maximum, replace the gears as a set, meaning change both.

Check the bearings (many manufacturers use ball bearings instead of bushings in high capacity pumps there

by reducing the frictional losses) --if the ball bearings produce a crude noise, when turned with the hands,

then they need to be changed

Check the mechanical oil seals, if lips are worn or slightly damaged, it has to be renewed.

If the overhaul is for the PMS or condition-based monitoring program, it is better to change the oil seal/

bearings, it is always good to change the mechanical oil seals whenever the pump is dismantled.

Clean the joint sitting places on both the main shell and back cover correctly if the joints are damaged, should

be replaced

Once completed, the screws have to be assembled and boxed up, make sure to hold the back cover correctly

and in place while the screw shafts kept in their position.

Make sure to turn the drive shaft with hand and should turn without any wobbling.

The back cover is tightened properly with the new joint. The drain plug is put in place

The inlet and the outlet pipe lines are fitted to the pump with the proper thread seals.

Remember that the pump is to be placed in the cleaned foundation, with the correct shims in place. Then

move the motor in such a way that both the flanges are close to each other remember to keep the shims if

any, under the motor feet, correctly. Please check if there is any glaring misalignment.

CHAPTER-5

STEERING GEAR

Onboard the ship steering gear is used to steer the ship to a desired Heading. It is imperative that

steering gear system is maintained in good condition.

Before carrying out any maintenance routine, the maker's manual should be studied and thoroughly

understood. We have two types of electro hydraulic steering gear systems which are common in

today's marine application.

They are ram type and rotary type. Before moving into maintenance details of steering gear system,

a class four engineer should be in a position to understand how a steering gear looks like.

Maintenance chart

Daily checks

o Inspect the sliding and moving parts for sufficient lubrication.

o Check for sufficient quantity of grease and for proper functioning of greasing mechanism.

Automatic

o greasing is done in present day systems when the steering gear is in operation.

o Inspect all connecting linkages.

o Inspect pump seals, pipe connections for leakages.

o Check for sufficient oil level in the reservoirs.

o Check for temperature and pressure of the hydraulic oil, any deviation from normal values.

o Check the running hydraulic pump for correct functioning. Check the ammeter reading of the

pump.

Check level of following:

o Replenishing tank

o Storage tank- One complete System replenishment.

Every week

o Check various alarms and emergency changeovers.

o Check the communication from bridge to steering room. Repeat the procedure with sound

powered telephone.

Every month

o Check and clean hydraulic oil filters or replace them as per makers recommendation.

o Every three months Try out emergency steering from local control station in steering and log

down in log book.

Every six months

o Collect hydraulic oil samples and send the same to ashore for laboratory analysis.

Every dry-dock

o As per continuous survey of machinery (CSM) complete overhaul of steering gear system

which includes replacement of ram seals, measurement of bearing wear down etc.

Operational Aspects of Steering Gears

When special cautions are required to be exercised during navigation, ships must have more than one

steering gear power unit in operation when such units are capable of simultaneous operation.

Within 12 hours before departure, the ship’s steering gear shall be checked and tested by the ship’s

crew. The test procedure (see below) must include, where applicable, the operation of the following:

1. The main steering gears

2. The auxiliary steering gears

3. The remote steering gear control systems;

4. The steering positions located on the navigation bridge;

5. The emergency power supply;

6. The rudder angle indicators in relation to the actual position of the rudder;

7. The remote steering gear control system power failure alarms;

8. The steering gear power unit failure alarms; and,

9. Automatic isolating arrangements and other automatic equipment as required for the steering

gear.

Manufacturer’s recommendations / owner’s instructions must be strictly followed

The above checks and tests must include: (⌂)

o The full movement of the rudder according to the required capacity of the steering gear;

o A visual inspection of the steering gear and its connecting linkage; and

o The operation of the means of communication between the navigating bridge and the steering

gear compartment

(⌂) – The deck department should be informed for ensuring that there are no obstructions in the way

of the rudder. In excessively cold ambient temperatures, the heating system in the steering gear

compartment or any other oil-heater if provided, should be used. At ambient temperatures below 10°

C, as the oil warms up, the gear should be moved slowly, in order to heat the complete hydraulic

system. The power units should be run for about 30 minutes prior departure to raise the oil

temperature and occasional rudder movements made, to facilitate a uniform system temperature. The

oil level in the supply tank should be checked and topped up to about 75% of its capacity. Where

arrangements are provided, the low level alarm should be tested.

The duty engineer should check that, the linkages are free for satisfactory operation, the sliding

surfaces are duly lubricated and whether there are any leakages in the hydraulic oil. Rams ought to be

lubricated with the system oil. The individual grease nipples or the central greasing system, if fitted

for the ram guides, are to be verified for their being full and whether lubrication is being provided.

The “connecting pin” should be removed from the “steering from navigating bridge position” and

inserted into position for control of the “steering (by the trick wheel) from within the steering gear

compartment”. The rudder should be moved from hard-over to hard-over, using each power unit in

turn before cutting-off the power to test the audible and visual alarms on the bridge. Simultaneously,

the position of the tiller as indicated in the steering gear compartment should be verified against the

position indicated on the bridge by the rudder angle indicator, utilizing the communication system

provided. The indicating-light provided on the bridge to demonstrate the running motor of the power

unit in service, should be verified for satisfactory operation.

The “connecting pin” is restored in position for “telemotor steering” and then the tiller should be

operated from the bridge, by using the portpower-unit, to start with as an example. Now disconnecting

the power supply to this port-unit, would test the effectiveness of the automatic startup

arrangements(if provided) by bringing into service the starboard unit, which could have been

otherwise be started manually from the bridge.

This test may be repeated by starting with the starboard motor.

With both the power units running, opening the power supply breaker and then closing it would check

the automatic restart arrangements. Each control system provided ought to be tested.

The level of the hydraulic fluid in the tank (reservoir), should be checked.

In case certain ships are provided with equipment in excess of that which are mandatory, all testing

and drill stipulations are to be made equally applicable to the non-mandatory equipment. Masters and

Chief Engineers are required to ensure that all equipment is checked and tested and also that their

respective officers concerned with the operation or maintenance of steering gears are familiar with

the operation of the steering systems as fitted on board, along with the procedures for changing from

one system to the other. Emergency steering drills must be conducted at least once every three

months. This will enable the practising of emergency steering procedures.

The drills must include direct control of the system within the steering gear compartment, the

feasibility of communications with the navigation bridge and, the operation of alternative power

supplies, as applicable.

Waivers may be given by the Administration from the checks and tests marked “(⌂)” above, to ships

which regularly engage on voyages of short duration. In such cases, the checks and tests are to be

carried out at least once a week.

Safe Isolation of the System

o Removed the auto standby pump from auto position

o Stopped the Electric motor of the hydraulic pump

o Control room circuit breaker put off

o Electrical isolation permit should be obtained and Local electrical panel circuit breaker put off

o Shut off relevant isolating valves on the piping circuit between pumps and the actuators /

storage tank / replenishing tank.

o Informed bridge

o Display 'men at work' warning board.

Filter Cleaning

Usually filter cleaning is carried out if the differential pressure drop across the filter is high or in some

cases the visual indicator located on the filter is in the “red level”.

Now, there are two different types of filters.

The inlet side of the pump is provided with a filter capable of removing chips with a filtration level of

50 microns.

Silt filters are positioned in the return line. They are also called as return line filters.

Procedure

o Filter cleaning is carried out in the following fashion.

o Isolation of the system should be carried out.

o Ensure that there is no pressure in the line. This is cross checked by opening the purge screw.

o The base of the filter is turned slowly.

o The filter bowl with the filter element is removed.

o The element is replaced for a new one.

o In some cases, if it is of fine mesh wire type, clean the same with solvent like kerosene. Then

with ultrasonic cleaning. (attach the you tube link provided).

o Blow off air in the filter element.

o Fit the element along with the filter bowl.

o Purge the filter till air free liquid is seen through purge plug, close the same.

o Start the pump and see to that no leaks are present.

o Give rudder movements and check there are no leaks.

System Oil Charging and Air Purging

System Oil Charging

o When replenishing the system after repairs, the guidance below should be followed:

o The charging system consists of a storage tank, storage tank outlet valve, hand pump and

delivery valve to oil reservoir tank fitted in line with the system.

o The storage tank capacity should be as per class requirements.

o Oil level is monitored by means of gauge glass fitted to the storage tank.

o Usually the storage tank is kept 90% full to cater to any emergency

o The storage tank capacity should able to cater a full charge for the complete hydraulic circuit.

o The position of all the valves in the system should match with name plate of the steering gear.

o The steering gear system should be changed over from remote to local control.

o Open storage tank outlet valve and valves on the hand pump.

o Open the respective oil reservoir filling valve, either #1 or #2.

o With the help of hand pump, fill up the respective oil reservoir.

o Oil level should increase in the oil reservoir and come down in storage tank.

o Do not overfill, as some ullage space has to be left for expansion and oil return.

o Shut the oil reservoir filling valve.

o Shut the storage tank outlet valve and hand pump valves.

Oil system air purging

The procedure refers to purging of air from 4 ram type steering gear system:

o Carry out the system isolation as mentioned before.

o In case of hydraulic ram type steering gear, the casing and the sump should be maintained with

75% of its capacity.

o Turning bar inserted in the holes of flexible coupling between motor and pump.

o The air release purge screws on the cylinders are then opened partially. Use correct allen key.

o The pump put on stroke by pressing the end button of the bi-directional valve.

o The gear is slowly moved from one direction to another. Ram movement should be on both

sides.

o The level in the tank should start to fall.

o Air free or bubble free liquid should escape through air release valves.

o Stop pressing the end button of the bi-directional valve and stop turning the pump.

o Switch on the breaker and Start the electric motor. Put the switch on local.

o Under local control, use bi directional valve to move the gear should be moved from one side

to another.

o The air release on the cylinders is noted and the gear is slowly moved from one direction to

another.

o The travel of the rams should be gradually increased, until air free oil is discharged.

o Pumps are changed over by change over switch.

o Ram movement is continued, first with one pump and then with other pump.

o Air release valves are checked periodically to ensure that air has been released.

o Tighten the air release purge screws.

o The system is cross checked by giving various helm movements from bridge and from steering

flat.

CHAPTER-6

REFRIGERATION AND AIR CONDITIONING SYSTEM

On-board ship refrigeration system is used to prolong the storage life of perishable goods, by lowering its

temperature such that metabolic deterioration is prevented. On the other hand, air conditioning is a process

by which condition of air is modified and maintained for human comfort.

Since a refrigeration system is used in carriage of food products and an air conditioning system for human

comfort; it is imperative that refrigeration and air conditioning systems are maintained in good condition.

Safe Isolation of the system

▪ Pump down the refrigerant in the condenser.

▪ Compressor cuts off on LP trip.

▪ cooling water run for 30 minutes

▪ Stopped the compressor

▪ Control room circuit breaker put off

▪ Electrical isolation permit should be obtained and Local electrical panel circuit breaker put off

▪ Shut off the cooling water as appropriate

▪ Shut off the refrigerant line valves

▪ Remove the compressor from auto start and from priority

▪ Display man at work warning board

Purging Out Air from the System

The symptom which indicates air in the system has a steady increase in the high-pressure gauge reading.

Accumulation of air reduces the effective area of condenser available for condensing refrigerant.

Close the condenser outlet liquid valve and compressor will trip on LP cut off. Sea water is left circulating

in the condenser for few hours to achieve equilibrium.

Note the HP gauge reading. If no air is present in the condenser, there will be no change in the reading. If

air is present, then the reading will be higher than the previous value.

The refrigerant will condense and collect in the receiver but air stratifies and collects on top of the

refrigeration liquid. Now crack open the vent cock to purge out air from the system.

Adding Oil to the System

▪ Replenish the oil when oil level is below half the sight glass.

▪ Manufacturer prescribed oil should only be used.

▪ Clean oil from sealed containers should only be used.

▪ Close the liquid valve at the receiver outlet and collect the refrigerant.

▪ The compressor will cut off on LP trip.

▪ Close the suction and discharge valves of the compressor.

▪ Note that no refrigerant is allowed to be released into atmosphere.

▪ Charging valve usually fitted on c/case. This valve is of non-return type.

▪ Remove the cap from charging valve and connect the hand pump out let with charging or filling

valve.

▪ Add oil to the crankcase using the hand pump.

▪ After charging the oil to required level, secure charge valve and fix the cap in place.

▪ Open the suction and delivery valves. Open the liquid receiver outlet valve. Start the compressor.

Cleaning of Oil Strainer

▪ Close the liquid valve at the receiver outlet and collect the refrigerant.

▪ The compressor will cut off on LP trip.

▪ Close the suction and discharge valves of the compressor.

▪ Open plug provided between compressor and suction valve, vent trapped gas in to retrieval gas bottle.

▪ Place a receptacle underneath the drain plug,

▪ Open the crankcase drain plug slowly and collect the crankcase oil.

▪ A suction strainer is attached to the drain plug. Clean the oil strainer.

Oil-Contamination in the Refrigeration System

The evaporator, compressor, condenser and expansion valve are essential components of refrigeration cycle.

The vapor-compression refrigeration system

uses a circulating liquid refrigerant as the medium that absorbs and removes heat from the space to be cooled

and subsequently rejects that heat elsewhere.

Oil in Reefer System

The oil has a key function in a refrigeration system because it contributes to ensure:

▪ Lubrication of the mobile parts of the compressor

▪ Evacuation of the heat due to frictions of the mobile parts

▪ Air tightness between the compression stages in reefer compressors.

The lubricating substances could be divided into natural mineral oils, synthetic oil and half-synthetic oil.

The mineral oils could further be divided into:

▪ With a small amount of aromatic hydrocarbons, known as paraffin oils;

▪ Oils with a majority of aromatic hydrocarbons, known as naphthalene oils;

▪ Oils with a majority of aromatic hydrocarbons supplemented by groups of simple or alkyl rings.

In the cylinder of positive displacement compressor where a lubricating substance is used as a sealing,

cooling and lubricating, during the lubricating of the cylinder’s smooth surface, an oil-film is emerging on

the cylinder’s wall. Furthermore, a partial dispersion of lubricating substance takes place in the working

space of the compressor that results in appearance of aerosol. As a consequence of the Piston’s forward-

backward movement and its friction against the cylinder’s wall, the wall’s temperature rises. If the

temperature is high enough, the wall “dries out”. The oil takes over the heat from the cylinder’s wall (cooling

function) and turns into vapour. In the compressor cylinder a structure of flux of the air and lubricating

substance mixture in the form of liquid, steam and aerosol is emerging. The type of oil, chosen so as not to

react with the refrigerant type and other components in the system.

Oil Separators

To enable the oil ejected of the compressor to return to the crankcase, it is necessary:

▪ To respect the speed in the pipes in order to ensure the circulation of oil. Especially when the

refrigerant is in gas stage as its miscibility with oil is low.

▪ To use an oil separator which function is to recover a substantial quantity of oil and to make it return

to the compressor as soon as possible.

In small refrigeration systems, the oil is allowed to circulate throughout the whole circuit, but care must be

taken to design the pipe work and components such that oil can drain back under gravity to the compressor.

As a cost-effective permanent solution, consider equipping the chiller with a

new, high-efficiency oil purges which removes oil and acid

In larger more distributed systems, especially in retail refrigeration, oil is normally captured at an oil

separator immediately after the compressor, and is in turn re-delivered, by an oil level management system,

back to the compressor(s).

The four main techniques selected in the design and the manufacture of oil separators intended to

refrigeration systems are:

▪ Coalescence: phenomenon into which two substances identical but separated, tend to concentrate.

▪ Centrifugation: this technique uses the centrifugal force in order to separate refrigerants with

different densities.

▪ Speed reduction: this technique enables the heaviest molecules to follow their trajectory, by inertia,

while the lightest molecules scattered into the internal volume of the oil separator.

▪ Change of direction: this technique, in association with the previous one, enables to improve the

efficiency of droplet separation (heavy molecules) present into the steam (light molecules). The

droplets keep their initial trajectory because of their mass and their initial speed, while steam is

directed towards the outlet connection of the oil separator.

The manufacturers of oil separators will select one or several separation techniques according to the level of

efficiency researched.

Coalescence can be obtained with metallic sieves or coalescent cores which will be then necessary to replace

regularly.

How Oil Separators Work

Oil separators are almost always made of steel. As oil-laden discharge gas enters the oil separator's very

large internal volume, it immediately slows down its velocity. This low velocity is the key to good oil

separation. The oil is mixed with the discharge gas in the form of a fog. This refrigerant/oil fog now runs

into internal baffling, which forces the fog mixture to change direction. At the same time, this fog mixture

is slowing down rapidly on the surface of these baffles. Very fine oil particles collide with one another and

form heavier particles. Finally, fine mesh screens separate the oil and refrigerant even farther, causing larger

oil droplets to form and drop to the bottom of the separator. Often, a magnet is connected to the bottom of

the oil sump to collect any metallic particles. When the level of oil gets high enough to raise a float, an oil

return needle is opened and the oil is returned to the compressor crankcase through a small return line

connected to the compressor crankcase. The pressure difference between the high and low sides of the

refrigeration or air conditioning system is the driving force for the oil to travel from the oil separator to the

crankcase. The oil separator is in the high side of the system and the compressor crankcase in the low side. This float-

operated oil return needle valve is located high enough in the oil sump to allow clean oil to be automatically

returned to the crankcase. Only a small amount of oil is needed to actuate the float mechanism. This ensures

that only a small amount of oil is ever absent from the crankcase at any one given time. When the oil level

in the sump of the oil separator drops to a certain level, the float will force the needle valve closed.

The oil return line from the oil separator to the crankcase should be just above room (ambient) temperature.

This is caused from heat conduction to the line from the hot oil separator. If the oil return line is cool or cold

to the touch, there may be liquid refrigerant vaporizing in it as it passes oil. This problem can result from the

oil separator's shell being poorly insulated and becoming too cool. If the shell is too cool, it can cool

discharge gasses too much, resulting in condensed (liquid) refrigerant in the bottom of the oil separator. This

will cause the float to rise too often because of increased levels of an oil and liquid refrigerant mixture in the

bottom of the separator. Once the float rises and the orifice opens, the mixture of liquid refrigerant and oil passes through the oil return line. The liquid refrigerant will vaporize from the sudden pressure drop and cause the cool temperatures in the return line.

Charging Refrigerant in the System

▪ Normally charging is made through the liquid charging valve at the high-pressure side.

▪ Put the drier in the system by opening the inlet and outlet of the drier valve and shut the by-pass

valve.

▪ Weigh the refrigerant gas cylinder before charging and after charging to ascertain the quantity of gas

charged in the system.

▪ Collect the gas by shutting the receiver outlet in the refrigerant system. The compressor will cut off

on LP trip. Check the liquid level in the sight glass.

▪ Connect the charging pipe to the refrigerant gas cylinder. The gas cylinder should be kept in vertical

position. Liquid valve in the cylinder should be used.

▪ Connect the charging pipe to the liquid side of the system and crack open the cylinder valve. This

will purge out any entrapped air. Tighten the charging connection.

▪ Open the charging valve and liquid valve in the cylinder. The liquid refrigerant will start flowing in

to the system.

▪ Start the compressor on "manual" and continue to charge the system. Observe the liquid level in the

sight glass.

▪ Close the charging valve and pumping down the entire charge until suction pressure just above zero.

▪ Stop the compressor and close the discharge valve.

▪ Cooling water kept running for some hours.

▪ Air is purged out through purging valve on condenser until the refrigerant gas appear at the valve.

▪ Close the gas cylinder liquid valve.

▪ Close the drier inlet and outlet valves and open the by-pass valve.

▪ Start the system by opening the receiver outlet valve and observe its efficiency for 20 minutes. Check

the liquid level in the receiver.

▪ If additional charging is required, repeat the procedure.

▪ Calculate the amount of refrigerant (charging) and enter the engine log book.

Leakage Rectification in the System

▪ In case of refrigeration system, the refrigerant is led by means of copper pipe.

▪ In many instances, the copper pipe will get holed.

▪ Permanent solution would be to renew the whole section.

▪ However owing to paucity of time, you should carry out some temporary arrangement to arrest the

leakage.

▪ Pump down the refrigerant in the condenser.

▪ Use ferrule connection to seal the leak. Cut the copper pipe using pipe cutter.

▪ Insert Ferrule female and female pieces.

▪ Use thread seal tape on top of the threads. Tighten the same.

▪ Open the refrigerant valves and confirm if the leakage has stopped.

▪ Note : Cold repairs possible using superfast drying plastic steel putty solutions or certain acrylic

solutions. But, cold repair is prefered to arrest the refrigerant leakagage temporarily and for short

period only.

Testing Compressor Discharge Valves

▪ Close the liquid valve in the receiver outlet and collect the refrigerant.

▪ The compressor will stop on LP trip.

▪ Shut the suction and discharge valves quickly.

▪ Observe the suction and discharge pressure gauges. If the discharge pressure falls roughly by 1 bar

and above in five minutes and simultaneously if suction pressure rises, then the discharge valve is

leaking.

Testing of Compressor Suction Valve

▪ Run the compressor under manual control.

▪ Close the suction valve slowly to prevent foaming of lubricating oil in the crankcase.

▪ With the suction valves shut, the compressor should develop a vacuum of 0.4 bar or more.

▪ This indicates the suction valves are ‘holding’ and functioning correctly.

Defrosting

A method of removal of frost, built-up on Evaporator coils. Defrosting should be done before snow thickness

exceeds ¼”.

Reasons for defrosting:

▪ Affecting heat transfer properties.

▪ Affecting air flow and circulation.

▪ Liquid back to Compressor.

Defrosting Systems:

▪ Water wash defrosting

▪ Hot gas defrosting

▪ Electric defrosting

▪ Manual shut down defrosting

▪ Warm brine defrosting

Various methods to defrost Brine System:

1. Hot brine thawing: Best and fastest method, used powerful brine heater with separate thawing

system. Watertight trays under the pipes, collected the dripping water.

2. Hot air from atmosphere: It is important that isolating doors in air trunks are perfectly tight, so as

to prevent hot air going into cargo spaces.

3. By shutting off brine : Allow the snows to be melted by the heat of the air in circulation. Very slow

operation and tends to throw back great deal of moisture into cargo space

▪ Direct expansion grid system: Hot gas defrosting.

▪ Battery cooling system: Water spray, electrical or steam heater.

▪ Brine cooling: Hot brine thawing.

Cargo Fridge Defrosting:

▪ In Battery System, hot brine passing brine heater is used.

▪ Steam is released to brine heater and brine flow is restricted by brine inlet valve, until brine

temperature has risen above 0°

▪ Brine temperature of 43°C is suitable for defrosting.

Cold Room defrosting and methods of defrosting

Coil Room is required to defrost to gain more Heat Transfer Efficiency.

Methods of Defrosting are:

▪ ( i) Plant stopped and manual watering

▪ (ii) Hot gas circulating

▪ (iii) Electric Heater.

Troubleshooting of Refrigeration System

Faults in Shipboard Refrigeration Systems

1. Undercharging of Refrigeration System

Indication:

▪ Compressor is running hot and performance of the compressor falls off due to high superheat

temperature at the suction side of compressor.

▪ Suction and discharge pressure of the compressor is low.

▪ Large vapor bubbles in the liquid sight glass.

▪ Low gauge readings in the condenser.

▪ Ammeter reading for the compressor motor is lower than normal.

▪ Rise in room temperature which is to be cooled.

▪ Compressor is running for extended period of time.

Causes:

▪ Leakage of refrigerant at the shaft seal, flange couplings, valve gland etc.

▪ Expansion valve may be blocked at the strainer.

▪ Partial blockage of refrigerant at the filter or drier or evaporator may cause undercharging.

Action:

▪ Identify and rectify the leakage of refrigerant from the system.

▪ Clean the filter and drier.

▪ Charge the system with fresh refrigerant as required.

2. Overcharge of Refrigeration System

Indication:

▪ The liquid level in the condenser is too high (high condenser gauge reading). This will reduce the

available condensing surface, with corresponding increase in the saturation temperature and pressure.

▪ High pressure switch of the refrigerant compressor activates and stops the compressor.

▪ The suction and the discharge pressures are high.

Causes:

▪ It may be due to the reason that excessive refrigerant has been charged in the system.

▪ Air in the system may also cause over charging indication.

▪ It may also be due to the formation office on the regulator.

Action:

▪ Remove the refrigerant from the system. This is done by connecting a cylinder to the liquid line

charging valve, starting the compressor, and then operating the charging valve.

▪ Purge the air from the system and maintain effective cooling.

▪ Remove ice from the regulator by using any of the defrosting methods.

3. Moisture in the System

This normally comes with the ingress of air in the system. Moisture may freeze at the expansion valve, giving

some of the indication of under charging. It will contribute to the corrosion in the system. It may cause

lubrication problems and breakdown of the lubricating oil in the refrigerant compressor.

Action:

▪ Renew silica gel in case of minor moisture.

▪ collect refrigerant and remove all air and moisture by vacuum pump if the amount is huge.

4. Air in the System

Indication:

▪ This may cause the refrigeration compressor to overheat, with a high discharge pressure and normal

condensing temperature.

▪ There are possibilities of small air bubbles in the liquid sight glass of the condenser.

▪ Condensing pressure of the refrigerant in the condenser may be high.

▪ If there is excessive air, it may reduce the cooling capacity of the system, making the compressor to

run for the extended period of time.

▪ It may cause the gauge pointer of the condenser to jump indefinitely.

Causes:

▪ During charging, air may enter in to the system.

▪ If Freon-12 is used air may leaks in to the suction line because the working pressure of the Freon-12

refrigerant is less than the atmospheric pressure.

Action:

▪ Air in the system can be removed by collecting the system gas in the condenser, leaving the condenser

cooling water on and venting out the air from the top of the condenser because air will not be

condensed in the condenser but remains on top of the condenser above the liquid refrigerant.

▪ Connect the collecting cylinder to the purging line of the condenser, open the valve, and collect air

in the cylinder.

▪ After purging the air from the system don’t forget to shut the purging valve.

▪ Check the level of the refrigerant in the system. If required, charge the system with fresh refrigerant.

▪ Restart the compressor with all safety precautions

5. Oil in the Refrigeration System

Indication:

▪ Temperature is not dropping in the cold rooms as normal, due to fact that oil act as insulation in the

evaporator.

▪ It may cause excessive frost on the suction line.

▪ Refrigerant compressor runs for the extended period of time.

▪ Lubricating oil level in the compressor will drop.

▪ Refrigerant level will fall if oil has caused blockage.

Causes:

▪ This may happen if the oil separator is not working properly.

▪ Oil may carry over from the compressor and may not come back to the compressor due to blockage

in the system.

▪ Defective piston rings or worn out liner of the compressor may cause the oil to carry over along with

the refrigerant.

▪ Compressor may take high capacity current during starting.

Action:

▪ Check the oil separator for proper functioning.

▪ Check the drier for proper cleaning and if its require cleaning clean it

▪ Evaporator coil should be drained to remove any trace of oil.

▪ If there is oil in the cooling coils, increase the condenser and evaporator temperature differentials

and remove excess frost on the suction pipe.

▪ Heat pipes with blow torch.

6. Flooding of Refrigerant in the System

This is seen as liquid getting back to the suction of the refrigerant compressor. It may be due to a faulty or

incorrectly adjusted expansion valve and also due to solenoid valve leakage. It may also result from

overcharging of the refrigeration system. Flooding may lead to an iced-up evaporator.

7. Evaporator Coil Icing:

Icing of the evaporation coils which may happen due to:

1. Cause: Too low temperature setting

Action: Increase the coil temperature by adjusting TEV or it’s sensor.

2. Cause: The coil capacity is less

Action: Install large capacity evaporator coils

3. Cause: Defrost is not operational

Action: Check if the defrost system is functioning at regular intervals.

8. Compressor Starts but Stops immediately

When the compressor in the reefer circuit starts and suddenly stops, it can be because of the following

reasons:

1. Cause: Low pressure cut out gets activated

Action: Ensure that all the suction line valves are in open condition, the refrigeration is properly charged

and the low pressure cut out is not defective.

2. Cause: Defective oil pressure cut out

Action: Check for proper functioning of oil pressure cutout and replace the defective cutout.

3. Cause: Defrosting timer is getting activated frequently

Action: If the defrost timer is getting activated frequently, leading to cutout of compressor, check and repair

defrost timer.

4. Cause: The lube oil level is below required level

Action: This can be because of leakage of lube oil from seal or carry over of oil. Rectify the leakage and

refill the oil level.

5. Cause: Foaming of oil leading to reduced oil pressure

Action: Ensure no foaming takes place, renew the oil if required.

6. Cause: Motor overload cutouts are activating

Action: Ensure that electrical motor trips are working properly.

9. Excessive icing up at Compressor suction:

Causes:

▪ Abnormal operation of TEV.

▪ Overcharge of the system.

▪ Moisture in the system owing to dirty Dryer.

▪ Defective Suction valve

Indication:

▪ Continuous running of Compressor.

▪ Insufficient cooling effects.

▪ Noisy operation.

▪ High suction pressure.

10. Defective Discharge valve

Indication:

▪ Continuous running of Compressor.

▪ Insufficient cooling effects.

▪ Noisy operation.

▪ High suction pressure during running.

▪ Low discharge pressure during running.

▪ Suction pressure rises faster after Compressor is shut-down.

▪ Warm cylinder head

11. Choked Expansion valve

Causes:

▪ Due to dirt and freeze-up of water present in system.

Effects:

▪ Starved Evaporator

▪ High superheat temperature.

▪ Rapid Condenser pressure rise can cause stopping of Compressor

Remedy:

▪ Clean Expansion valve and filter

▪ Renew Dehydrator.

Operation of DE Ref Plant

The refrigeration plant runs continuously to maintain the cold room temperatures. The compressor cuts in

and cuts out automatically, depending on the room temperatures. Two plants of the same refrigerating

capacity are provided so that one plant will be available during the maintenance of the other plant.

Temperatures of cold rooms are to be monitored periodically. A timer defrosts the evaporator coils located

in the cold rooms automatically, at the preset intervals. The refrigeration plant parameters monitored and

recorded, indicate the performance of the plant. The thermostats located in the rooms control the opening

and closing of the solenoid valve according to the required temperatures.

As the temperature of each room reaches the set value, its solenoid stops the flow of the liquid refrigerant to

that room. The temperatures of the vegetable and dairy room are maintained at 4°C to 5°C by a back pressure

valve fitted after the evaporator. The temperature at which the refrigerant evaporates depends on the

evaporator pressure. The back pressure valve maintains the evaporator at the required pressure.

Safety Devices

Safety devices protect the compressors from damage due to high refrigerant pressure or low luboil pressure.

The lube oil differential pressure cut out compares the lube oil pressure and the suction pressure of the

compressor. If the differential pressure falls below 1.2 bar, then the compressor trips and requires a manual

reset to restart. A time delay is built into the circuit to allow sufficient time for the lube oil pressure to build

up while starting.

The high pressure [HP] cut out is fitted at the delivery of the compressor. If the compressor delivery pressure

increases above the set value, then the compressor trips. It requires a manual reset to start the compressor.

The low pressure [LP] cut out trips the compressor in case the suction pressure drops below the set value. In

most of the plants, it is used for starting and stopping the compressor to maintain the temperatures.

The compressors are lubricated to:

▪ Reduce the frictional wear on bearings and moving parts

▪ Cool the refrigerant gas during compression

▪ Seal against refrigerant gas leakage

The refrigeration compressor lube oil should have the following properties:

▪ Outstanding low temperature fluidity

▪ Outstanding oxidation resistance and thermal stability at high temperatures

▪ Excellent deposit control

▪ Low volatility for lower oil consumption and less makeup oil

▪ Protection against rust and corrosion

The specifications preferred for the lubricants are given in the table below.

▪ ISO Viscosity Grade 68

▪ Viscosity Index 143

▪ Density @ 15 °C, g / cm3 830

▪ Flash Point, °C 230

▪ Viscosity at 40 °C, cSt 70

▪ Pour Point, °C -42

During running:

▪ Make vacuum pressure in crankcase and suck oil itself.

▪ Ensure oil pipe immersed in oil to prevent air ingress.

Stop condition:

▪ Tight shut both inlet and outlet valves of compressor.

▪ Open filling plug and fill to required level.

▪ Air purge to be done when plant resume.

Thermostatic Expansion Valve (TEV)

Functions:

▪ Reduce the pressure of the refrigerant: The first and the foremost function of the thermostatic

expansion valve is to reduce the pressure of the refrigerant from the condenser pressure to the

evaporator pressure. In the condenser the refrigerant is at very high pressure. The thermostatic

expansion valve has an orifice due to which the pressure of the refrigerant passing through it drops

down suddenly to the level of the evaporator pressure. Due this the temperature of the refrigerant

also drops down suddenly and it produces cooling effect inside the evaporator.

▪ Keep the evaporator active: The thermostatic expansion valve allows the flow of the refrigerant as

per the cooling load inside it. At higher load the flow of the refrigerant is increased and at the lower

loads the flow is reduced. It won’t happen that the load on the evaporator is high and the flow of the

refrigerant is low thereby reducing the capacity of the evaporator. The thermostatic expansion valve

allows the evaporator to run as per the requirements and there won’t be any wastage of the capacity

of the evaporator. The TEV constantly modulates the flow to maintain the superheat for which it has

been adjusted.

▪ Allow the flow of the refrigerant as per the requirements: This is another important function of the

thermostatic expansion valve. It allows the flow of the refrigerant to the evaporator as per the load

on it. This prevents the flooding of the liquid refrigerant to the compressor and efficient working of

the evaporator and the compressor and the whole refrigeration plant.

TEV construction:

▪ Small quantity of Vapour Refrigerant is sealed in a bulb or phial, and attached to Compressor suction

pipe, just coming out from Evaporator.

▪ Other end is connected by Capillary Tube to the chamber above Flexible Bellow in valve body.

▪ The space below the Bellow is in communication with Evaporator outlet pressure (this is called

Equalising Line)

▪ If no further action is taken, pressure above and below the Bellow will be equalised and hence no

superheat is obtained.

▪ This is overcome by providing adjustable Bias Spring under the Bellow, and Bias Spring pressure is

proportional to required superheat.

Operation:

1. Refrigerant Liquid from Condenser enters into TEV via Dryer, it expands to Evaporation Pressure,

and some flash gas is formed.

2. Flash Gas amount varies between 25 – 35%, depending on refrigerant type, plant capacity and

ambient temperature.

3. Mixture of this expanded gases and some part of liquid, passed into Evaporator, where complete

Evaporation takes place.

4. Evaporator outlet pressure plus Spring pressure tends to close the valve, and is opposed by the

pressure above the Bellow, trying to open it.

5. This pressure above the Bellow is in relation to temperature in Compressor suction pipe.

6. Equilibrium condition is reached, when Superheat is correct at phial attachment point.

7. Starved condition in Evaporator will result greater Superheat, so expansion of Vapour Refrigerant in

phial will tend to open the valve further, to increase the flow.

8. Flooded condition in Evaporator will result lower Superheat, so contraction of Vapour Refrigerant

in phial will tend to close the valve further, so decrease the flow.

9. Superheat Temperature adjusted at: 3 – 6°C, by Bias Spring pressure.

Equalising Connection

▪ In some plant having large Evaporator or Multi-circuit Evaporator, excessive pressure drop across

Evaporator occurs, and always tend to starve the Evaporator and increase the Superheat.

▪ To counteract this, if pressure drop across Evaporator, exceeds 3 bar, an Equalising Connection must

be provided at TEV.

▪ A direct connection between underside of Bellow and suction piping of Compressor, preferably

between phial and Compressor.