ENGINEMAN 1 & Caid in keeping the air supply clean, filters arefitted to compressor intakes. Unless inspected andcleaned regularly, these filters become clogged andcause a loss of capacity.Filter elements should be removed from theintake and cleaned either with a jet of hot wateror steam, or by immersion in a strong solutionof sal soda. The filter body should be drained andreplaced. Filter elements of the oil-wetted typeshould be dipped in a clean, medium viscosity oilafter cleaning and the excess oil should bedrained from the elements before replacing themon the filter intakes. Gasoline or kerosene shouldnot be used for cleaning air filters because of theexplosive fumes which may collect in the com-pressor or air receiver.DehydratorsOn some ships, compressed air is used for theoperation of missile system components and withautomatic controls for boilers. In order to pre-vent failure of these systems, moisture andlubricants from the compressor must be kept ata minimum. Blowing down the compressorseparators prevents most of this, but still somemoisture is carried over.To aid in the removal of the moisture andlubricants, two types of dehydrators are gener-ally used: type I refrigerant dehydrators and typeII dehydrators using a desiccant of either silicagel or activated alumina, and containing electricheating coils for reactivating the desiccant whenit becomes saturated with moisture. Type IIdehydrators are normally installed in pairs so thatone can always be in service while the other is be-ing reactivated.Air ValvesAir inlet and discharge valves are vital partsof a compressor and should receive careful atten-tion. When these valves leak, the compressorcapacity is reduced and results in an unbalancedstage pressure.There are several symptoms which signify thatan air valve is not functioning properly. A devia-tion from normal intercooler pressure mayindicate a leaking or broken valve. A defectiveinlet valve above the intercooler will cause a risein pressure in the intercooler, while a defective7-2discharge valve below the intercooler will causea decrease in the intercooler pressure. An unusu-ally hot valve cover is a sign of valve trouble.Dirt is generally the cause of leaking valves.The source of valve trouble can usually be tracedto dirty intake air; the use of excessive or impropercylinder oil; or excessively high air temperature,resulting from faulty cooling. A periodic inspec-tion and cleaning of valves and valve passages willminimize and perhaps prevent the occurrence ofair valve troubles. The frequency for cleaningvalves must be determined for each installation.The air valves are easily accessible and areremoved by first loosening the valve cover plates.Then the valve and valve unloader, if installed,may be lifted out. Each valve should be markedso that it may later be returned to the same open-ing from which it was removed.Dirt or carbon can usually be removed fromvalve parts without disassembling the valve. Ifdisassembly is necessary, notice should be takenon how the various parts are arranged so that theproper relationship will be kept when the valveis reassembled. To remove carbon from valveparts, soak each part in kerosene and then brushor scrape lightly. After drying and reassemblingthe valve parts, test the valve action to be surethat the valve opens and closes freely.Before air valves are replaced in a cylinder,inspect the gaskets. If the gaskets are made ofmaterials other than copper, and are damaged,change them. Copper gaskets should always bereplaced. Since it is often difficult to distinguishbetween suction and discharge valves, use extremecare when inserting valves in the cylinder. Makesure that suction valves open TOWARD, anddischarge valves AWAY FROM, the center of thecylinder. Otherwise, serious damage or loss ofcapacity will result. If special locknuts are not pro-vided to seal against leakage at the threads of thevalve setscrew, place a turn of solder or fuse wirearound the screw and set down into a recess bythe locking nut.Cylinders and PistonsWhen you find that it is necessary to inspectthe cylinders or pistons of an air compressor, youshould refer to the manufacturer’s instructionmanual and the appropriate Planned MaintenanceSystem (PMS) maintenance requirement card
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