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RDSO/PE/SMI/AC/0001-99 (REV.’1’)
Dated 26.02.99
SPECIAL MAINTENANCE INSTRUCTIONS ( Proper quality of brazing of refrigerant pipe )
1. TITLE :
Guidelines for ensuring proper quality / type of copper tubes and brazing material
to be used and procedure for brazing two refrigerant lines.
2. APPLICATION:
Roof Mounted A/C Package Unit provided on air-conditioned coaches.
3. REASONS AND OBJECTIVE FOR INSTRUCTIONS :
During field service of RMPUs, a large number of cases of gas leakage have been reported by Railways . Most of these leakage are contributed due to either cracks
developed in refrigerant copper tubes or due to failure of brazed joints . This SMI is therefore being issued with the intention to advise Railways and RMPU’s
manufacturers the followings:
(i) quality/ type of copper tubes to be used for refrigerant lines,
(ii) types of brazing materials to be used for joints between refrigerant tubes of different metals,
(iii) brazing procedure and precautions to be taken while making joints.
4. REFERENCE DRAWING : Nil
5. MATERIAL REQUIRED:
Oxy-acetylene brazing torch, copper tubes as required , brazing material , oxygen & acetylene gas and brazing flux etc..
6. DETAILS OF SPECIAL INSTRUCTIONS:
6.1 QUALITY / TYPE OF COPPER TUBE:
(i) The tubes to be used for refrigerant lines should be of soft annealed grade - 1 of copper conforming to IS:10773-1995.
(ii) The wall thickness of tubes should be not less than 1mm whenever replaced on old RMPUs while brazing and also during manufacturing
of new RMPUs.
(iii) After procurement of tubes carry out at least following tests as per IS: 10773-1995 to ensure proper quality of tubes.
(a) Drifting Test: As per IS: 2335-1985 :
The tube shall be capable of undergoing drifting by means of taper drift having an included angle of 45 deg. as shown in figure, given below, signs showing
either crack or flaw until the outside diameter of expanded end measures at least 40% more than the original diameter of the tube upto19 mm outside diameter of the original tube and that of 30% for tubes having original OD over 19 mm.
The light annealed and light drawn tubes shall be fully annealed before drifting test is done.
Fig. : Drifting Test
(b) Flattening Test:
This test shall be carreid out as per IS:2328-1983. The test piece shall be annealed before flattening unless the tubes are specified in
the annealed condition. A piece of tube shall be flattened down until the interior surface meets as drawn in fig. given below and shall then show NO sign of
cracking.
Fig. : Flattening Test
(c ) Mercurours Nitrate Test:
Although, this test has been deleted in the latest revision of IS:10773-1995 but this test shall be carried out in accordance with IS:2305-1988 as a special
requirement. Any piece under going this shall not show any sign of cracking.
6.2 TYPES OF BRAZING MATERIALS:
(i) For making brazed joints between copper & copper/ copper alloy brazing material BACUP3 to IS:2927-1975 should be normally used. Where close fit
is not achieved BACUP5 should be preferred.
(ii) For end brazing joints between copper with steel BACUAG-16 should be used.
7. BRAZING PROCEDURE AND PRECAUTIONS :
(i) Brazing should be done by a well trained experienced personnel.
(ii) For strong high quality joints, the surfaces to be joint must be cleaned and free from oil, dirt, grease and oxides,
otherwise capillary action may not take place.
(iii) In case of lap joint, the overlap shall be kept at about three times the thickness of thinner tube to ensure the proper strength of joint.
(iv) The overlap should not be kept more than as stated above as it may be harmful due to insufficient penetrations and inclusions etc.
(v) For making butt joint the faces should be properly cleaned by emery paper and faces should properly matched.
(vi) The joint clearance should be as per table 12 of IS:2927-75 but not less than 0.025 mm and more than 0.25 mm in any case. It adversely affects the
joint if not strictly followed.
(vii) Over-heating of base metal should be avoided as it may develop cracks due to expansion and contraction of base metals particularly in combination
joints. It also avoids undesirable dilution and diffusion in base metal.
(viii) The placement of filler metal can affect the quality of joint. For a lap joint the filler metal should be supplied at end and allowed to flow
completely through the joint by capillary action to avoid gas entrapment. Otherwise the joint may not be leak proof and of reduced strength.
(ix) The filler metal can not flow by capillary action into a blind joint.
(x) It is essential to remove all flux residue (if flux used) after brazing work, otherwise it may corrode the base metal. The cleaning may be carried out
by hot running water.
(xi) The brazed part must be inspected visually. For visual inspection, it is advised to keep standard sample for comparison and subsequent
acceptance and rejection.
(xii) Leak testing of joints may be carried out at a pressure 24.6 kg/sq.cm (350 psi)
(xiii) RDSO’s SMI No.ELPS/AC/SMI/14 (Procedure for charging refrigerant. in RMPUs) should be followed while gas charging.
8. PERIODICITY OF IMPLEMENTATION OF THE SMI :
i) At primary & secondary maintenance depot and POH shops whenever required.
ii) works of RMPU’s manufacturers during manufacturing of RMPUs.
9. AGENCY FOR IMPLEMENTATION :
9.1 At primary and Secondary maintenance A/C depot by air conditioning staff.
9.2 At POH shops by workshop staff.
9.3 At the works of RMPUs manufacturers.
10. DISTRIBUTION :
As per distribution list enclosed.
Enclosures : Nil
Sd/-
(M. P. Singh)
Krite Maha Nideshak (EMU &PS) Home
RDSO/SMI/AC/14.
No. EL/7.2.2 Dated 17/18.11.1997
SPECIAL MAINTENANCE INSTRUCTIONS ( Procedure for charging refrigerant gas in RMPUs. )
1. TITLE :
Procedure for charging refrigerant gas in RMPUs.
2. APPLICATION :
Roof Mounted A/c Package Units provided with sealed compressors.
1. OBJECTIVE:
This SMI is issued to advise Railways the proper procedure of refrigerant gas
(R22) charging and precautions to be exercis ed. Gas charging becomes necessary
in the event of system developing leakage, replacement of compressor or
replacement of any other equipments or gas pipe line in the system.
2. MATERIAL REQUIRED:
Vacuum Pump, Spring balance, Nitrogen gas cylinder, R22 gas cylinder, Halogen
leak detector, soap solution, brazing alloy alongwith brazing gas and other
accessories.
3. CHECKING THE SYSTEM FOR LEAKAGE :
Leakage check shall be carried out in following sequence:
(i) Fill in the system with dry nitrogen gas at pressure 250 to 300 psi (17.5 to 21 kg/sq.cm) through charging point at compressor.
(ii) Check for any leakage by applying soap solutions at all joints and other suspected points. The leak will be evident by the formation by bubbles.
(iii) After identifying the leakage, release Nitrogen gas from the system.
(iv) Carry out repairs to seal the leakage by brazing.
(v) Check the leakage again as explained above from (i) to (iv) and ensure the system is leak free.
6. EVACUATION OF THE SYSTEM :
After ensuring leak free system, the system should be evacuated to prevent ingress of moisture into the system. Because slight amount of moisture in the
system will inevitably lead to trouble in the following form :
(a) Corrosion of steel parts;
(b) Sludging or gumming, affecting lubrication,
(c) Choking of strainer or capillary due to ice formation at low temperature points affecting refrigeration,
(d) Corrosion of the bellows.
The system should therefore be evacuated by a vacuum pump upto 200 microns (29.9” of mercury column), and vacuum to be kept for four hours. If the vacuum
stays stable, then the system is ready for charging.
7. GAS CHARGING :
- Charge the system through charging line with 2.8 kg R22 gas.
- Quantity of gas charge is critical, therefore, it must be weighed by recording the weight of the refrigerant gas cylinder before and after charging. The difference
should be 2.8 kg.. Check for gas leakage with halogen leak detector after charging.
- Run the unit, check the compressor current and cooling.
- Seal the charging line by pinching ensuring the length of pinched charging line not to exceed 50 mm in case of KCL compressor type MG52F and remove
external charging pipe in case of Maneurope compressor MT56-HL4 and MT57-HL4.
8. APPLICATIONS:
All air-conditioned coaches provided with roof mounted AC package units.
9. AGENCY FOR IMPLEMENTATION :
All Carriage and Wagon Workshops carrying out POH of A/C coaching stock.
All air-conditioning depots maintaining AC coaches.
10. DISTRIBUTION :
As per the enclosed Distribution List.
Encl: Nil
Sd/-
(M.P. Singh)
For Director General (EMU & PS) Home
RDSO/SMI/AC/5
No. EL/7.1.83 Dated : Sept` 81
SMI.( Adequate dehydration of refrigeration system – Prevention of ingress of moisture. )
1. TITLE:
Adequate dehydration of refrigeration system – Prevention of ingress of moisture.
2. APPLICATION:
All types of air-conditioned coaches on Indian Railways.
3. OBJECT:
Too much emphasis cannot be placed on the importance of maintaining the system free from moisture. Slight amount of moisture in the system will
inevitably lead to trouble in the following forms:-
i) Corrosion of steel parts;
ii) Inter-crystalline corrosion of the bellows;
iii) Copper plating of shafts and bearings;
iv) Slugging or gumming of the oil;
v) Plugging of the strainers;
vi) Freezing and choking of the expansion valves.
4. DETAILS OF SPECIAL INSTRUCTIONS :
4.1 The main source of moisture is by leakage with air. In order to prevent ingress of
moisture in the sealed refrigeration system, the pressure in all parts of the system are always maintained higher than the atmospheric pressure as detailed below :
Suction 37 to 40 psi 2.6 kg/sq.cm to 2.8 kg/sq.cm Discharge 180 to 220 psi 12.6 “ to 15.5 “
Oil pressure 82 to 90 psi 5.6 “ to 6.3 “
This ensures that in case the initial charging of gas was done properly, there will be no chance for the outside air to leak inside. The only leak possible is for the
refrigeration gas to leak out.
4.2 PRECAUTIONS:
4.2.1 Before initial charging of gas, it is very important that adequate vacuum is created in refrigeration system so that as much air as possible is evacuated. Vacuum
should be created with the help of 2 h.p. rotating type pump to a level of 500 microns. The vacuum reading should be taken with the help of a good gauge
which can read up to 50 microns. Use of Macleod gauge or equivalent is recommended for this purpose.
4.2.2 Where suitable vacuum pump is not available, the vacuum up to 735 mm (29”)
may be created with the help of compressor as an alternative. After creating vacuum as stated above, the refrigerant should be released to the system sufficient
to create a pressure of 16 p.s.i. (11.2 kg/sqcm.). Then vacuum should be again created to 735 mm and this process should be repeated twice before initial
charging of the system is done.
4.2.3 The gas used should be free from moisture and foreign matter. Always charge
with gas cylinder upright, that is the valve up, so as to avoid drawing out any foreign matter that may be in the cylinder. During this operation, the cylinder will
become cold and the transfer of refrigerant can be accelerated by applying gentle heat to the cylinder.
4.2.4 It is strongly recommended that a suitable filter-cum-dehydrator should be
provided in the charging line which will remove any moisture and foreign matter that may be present.
4.2.5 The refrigeration equipment once commissioned such as condenser, evaporator and pipe work should never be allowed to have air. These should always be filled
with nitrogen which should be kept at a pressure of 16 to 17 p.s.i. (11.2 to 11.9 Kg/sq.cm.) with both ends properly and hermetically sealed.
4.2.6 For pressure testing of refrigerant equipment use nitrogen.
4.2.7 Air and non-condensible gases in any system collect in the receiver above the
liquid. These can be removed by purging from the top of the liquid receiver through the purge valve provided. To purge, stop the compressor for 10 to 15
minutes and then open the purge valve for a few seconds. Note any decided difference from the initial pressure when the valve is again closed. Repeat the
operation until the pressure is approximately equal to the refrigerant vapour pressure corresponding to the temperature of the receiver.
(“See Physical Properties of Freon at Annexure).
4.2.8 A liquid filter and drier unit is provided between liquid receiver and expansion valve. It consists of a shell containing two cylindrical core of activated Alumina
which absorbs and holds any moisture that may be in the system. These cores have a porous structure also serves to filter dirt from the liquid refrigerant. When
the cores have absorbed a certain amount of moisture, they become saturated and no longer effective in removing moisture and have to be replaced with new ones
or old re-activated cores.
4.2.9 If there is much dirt in the system, the pores may, after a period of time, become
clogged and will restrict flow of refrigerant liquid. This condition can be determined by feeling the inlet and outlet connections when the equipment is
operating; normally there should be no appreciable difference in temperature. If the outlet connection is colder than the inlet, new cores should be fitted as the old
cores are clogged. In some of the dehydrator silicagel is also used in place of activated Alumina, in
such cases a separate filter is provided after the dehydrator.
4.2.10 In coaches where liquid line sight glass cum moisture indicator is provided on the
refrigerant control panel, it is very easy to detect the presence of moisture. The disc in the centre of the sight glass will be normally green. When the disc colour
changes to yellow, it is a clear indication of presence of moisture and the dehydrator should be changed and the moisture should be removed by circulating
the refrigerant through the dehydrator till normal green colour of the disc is restored.
4.2.11 No portion of the refrigeration system should be kept under vacuum for long as this will encourage leaking of air into the system.
5. PERIODICITY OF IMPLEMENTATION OF THE SMIs:
Whenever the refrigerant is charged into the refrigeration system, the system
should be dehydrated.
6. EQUIPMENT REQUIRED :
(i) Rotary vacuum pump, 2 h.p.
(ii) Filter cum dehydrator
(iii) Macleod or equivalent vacuum gauge which can read upto 50 microns.
7. Do’s and DON’Ts
7.1 DO’s :
7.1.1 To watch regularly sight glass cum moisture indicator where provided and replace dehydrator element promptly as and when necessary.
7.1.2 Always use nitrogen for pressure testing of refrigeration system.
7.1.3 Always fill the refrigerant pipes, etc., with Nitrogen when refrigerant gas is taken out and system is to be kept without refrigerant gas over long period.
7.1.4 Always charge by keeping the gas charging valve up.
7.2 DON’Ts :
7.2.1 Do not use air or CO2 for pressure testing or filling up of refrigeration system in the absence of refrigerant gas. Both of these contain moisture.
7.2.2 Do not keep any portion of refrigeration system under vacuum for long time because this will encourage leakage of air from outside.
7.2.3 Do not apply naked flame to the gas cylinder directly while charging. It is a good practice to keep the cylinder in a bucket of water which may be heated as and
when necessary with the help of blow lamp.
8. AGENCY FOR IMPLEMENTATION:
(i) Workshop Staff (Electrical).
(ii) Air-conditioning Staff at Primary Maintenance Depots.
9. DISTRIBUTION:
As per distribution list.
Sd/-
(P.K. Khuller)
for Director General (Elec)
R.D.S.O., MINISTRY OF RLYS.
LUCKNOW-226011 Home
RDSO/SMI/AC/16
No. EL/7.1.83/J-9 Dated 29.5.1998
SPECIAL MAINTENANCE INSTRUCTION (Cleaning of copper tubes and fins of air-cooled condenser )
1.0 TITLE :
Cleaning of copper tubes and fins of air-cooled condenser unit used in underslung type air-conditioned coaches.
2.0 APPLICATION :
All types of air-conditioned coaches fitted with under-slung type equipments.
3. REASON AND OBJECTIVE FOR INSTRUCTION:
3.1 Cleaning of condenser plays vital role in the performance of air-conditioning system.
3.2 During normal working, deposition of dirt and dust on the tubes and fins of the condenser coil results in reduction of heat transfer capacity. Therefore, this SMI is
being issued for proper cleaning of the condenser unit of under-slung type AC coaches with different chemicals (Reinilon) in situ condition and also during POH.
4 REFERENCE DRAWING : Nil.
5 DETAILS OF SPECIAL INSTRUCTIONS:
5.1 Process of cleaning of condenser in situ condition (when the coach is available for a short period).
5.1.1 Spray water on the contaminated surfaces of the condenser with the help of jet connected to water pump (approx. pressure 70-80 psi) to remove dirt and dust.
5.1.2 After wetting the condenser thoroughly from both sides apply a suitable nonflammable descaling compound with inhibitor conforming to the requirements of the standard given in Table-1 of Annexure-1 on individual fin through a small capillary tube connected to a tank kept at height of approx. 2 metres. The feed of
this descaling compound should be by gravity only and no pressure should be applied to ensure removal of scale.
5.1.3 After a gap of 10 minutes, spray water on the condenser as mentioned in 5.1.1.
5.1.4 After the above treatment, apply suitable decarbonizer solution with the help of a jet at a pressure of 70-80 psi conforming to requirements of the standard given at
Table-2 of Annexure-1 to ensure complete removal of oil, grease and carbon deposits.
5.1.5 After a gap of 10 minutes wash the condenser with water jet for removal of the chemical.
5.1.6 Apply a suitable neutraliser solution conforming to the requirements given at Table-3 of Annexure-1 to ensure that treated surface is neutral.
5.1.7 Finally rinse the condenser with water jet to get bubble formation to see through and through both the sides of condenser to ensure thorough cleaning of the
condenser. The appearance of the true colour of the copper shall be taken as the end of the treatment.
5.2 PROCESS OF CLEANING OF CONDENSER AT THE TIME OF POH:
5.2.1 Remove the Condenser Unit from the underframe of the coach.
5.2.2 Immerse the condenser unit in a M.S. Tank having acid resistant lining containing the descaling chemical for 2 hrs.
5.2.3 After descaling wash the condenser with water jet at a pressure of 70-80 psi.
5.2.4 Immerse the condenser unit for one hour in a M.S. tank containing decarbonizer solution to ensure removal of grease, oil and carbon deposits.
5.2.5 After decarbonising, wash the condenser with water jet at a pressure of 70 -80 psi.
NOTE :
1. The size of the tank shall be commensurate with number of condensers to be treated.
1. The chemicals manufactured by M/s Reinol Obstfeld India Ltd., B-93, Mayapuri Industrial Area, Phase-I, New Delhi 110 064 under the brand name
“Reinilon” conforming to requirement of Table-1, 2 and 3 have been approved by M&C Directorate of RDSO for cleaning of copper tubes and fins of condensers
of under-slung type AC Coaches. It shall be ensured that these chemicals shall not be procured from sources other than RDSO approved sources.
6 PERIODICITY OF IMPLEMENTATION OF SMI:
i) At the Primary Maintenance depot during 3 monthly schedules.
ii) At the workshop during POH.
7 AGENCY FOR IMPLEMENTATION :
(1) Air-conditioning staff of Primary Maintenance Depot during 3 monthly schedules.
(2) Workshop Electrical Staff during POH.
8 DISTRIBUTIOIN :
As per enclosed distribution list.
Encl: Annexure- 1 & 2
Sd/-
(M.P. Singh)
Krite Maha Nideshak (EMU&PS) Home