A, the circular grooves that form chamber A are put incommunication with the unloader connections. Thisadmits high-pressure oil to the unloader cylinder andactuates the unloader mechanism.A capacity control regulating valve controls oilpressure from the capacity control valve. It is connectedto the crankcase and has an oil-connecting line tochamber B of the capacity control valve. As thecrankcase or suction pressure pulls down slightly belowthe setting of the regulating valve, the regulator opensand relieves oil pressure from chamber B of the capacitycontrol valve. This permits spring A to push the capacitycontrol piston one step toward chamber B, uncoveringthe unloader connection nearest the end of the capacitycontrol valve. This relieves oil pressure from the powerelement and allows the power element spring to rotatethe cam rings and unload the cylinder.If the suction pressure continues to drop, theregulator will relieve more oil pressure and unload morecylinders. If the heat load increases, the suction pressurewill increase, causing the regulating valve to close andload more cylinders.MAINTENANCEAs an Engineman, maintaining the refrigeration andair-conditioning plants may be one of yourresponsibilities. To do this, you must understand themaintenance procedures. In most instances, personnelwho are assigned to maintain refrigeration plants aregraduates of the Navy’s air-conditioning andrefrigeration school. This school teaches most operatingand maintenance procedures. However, you shouldrefer to the manufacturer’s technical manuals for thedetails of the plants on your ship.Testing Suction and Discharge ValvesFaulty compressor valves may be indicated byeither a gradual or a sudden decrease in the normalcompressor capacity. Either the compressor will fail topump, or the suction pressure cannot be pumped downto the designed value, and the compressor will run forabnormally long intervals or continuously. You may geta rapid buildup of suction (crankcase) pressure duringan off cycle. This causes the compressor to start after avery short off-period and indicates leaking dischargevalves.If the refrigeration plant is not operatingsatisfactory, you should first shift the compressors andthen check the operation of the plant. If the operation ofthe plant is satisfactory when the compressors have beenshifted, the trouble is in the compressor and not in thesystem.To test the compressor discharge valves, pumpdown the compressor to 2 psig. Then stop thecompressor and quickly close the suction and dischargeline valves. If the discharge pressure drops at a rate inexcess of 3 pounds in a minute and the crankcase suctionpressure rises, this is evidence of compressor dischargevalve leakage. If you must remove the discharge valveswith the compressor pumped down, open the connectionto the discharge pressure gauge to release dischargepressure on the head. Then remove the compressor tophead and discharge valve plate. Be careful not to damagethe gaskets.If the discharge valves are defective, replace theentire discharge valve assembly. Any attempt to repairthem would probably involve relapping and wouldrequire highly specialized equipment. Except in anemergency, such repair should never be undertakenaboard ship.You can check the compressor internal suctionvalves for leakage by following these steps:1. Start the compressor by using the manual controlswitch on the motor controller.2. Close the suction line stop valve gradually toprevent violent foaming of the compressor crankcaselubricating oil charge.3. With this stop valve closed, pump a vacuum ofapproximately 20 in.Hg. If this vacuum can be readilyobtained, the compressor suction valves are satisfactory.Do not expect the vacuum to be maintained after thecompressor stops, because the refrigerant is beingreleased from the crankcase oil. Do not check thecompressor suction valve efficiency of operation for atleast 3 days. It may be necessary for the valves to wearin.However, if any of the compressor suction valvesare defective, you can pump down the compressor, openit, and inspect the valves. Replace defective valves orpistons with spare assemblies.Crankcase Seal RepairsThere are several types of crankcase seals,depending on the manufacturer. On reciprocatingcompressors, the crankshaft extends through thecompressor housing to provide a mount for the pulleywheel or flexible coupling. Now the shaft must be sealedto prevent leakage of lubricating oil and refrigerant. The5-4
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