2. A dew point temperature reading of -40°F orlower at 80 lb/in2 is normal for LP (type II and type III)dehydrators. A reading of -20°F or higher at 80 lb/inindicates that the dehydrator is not operating properly,and you should check the applicable technical manualto correct the problem.3. For HP air dehydrators, a dew point temperaturereading of -60°F or lower at atmospheric pressure isnormal. A reading higher than -60°F at atmosphericpressure indicates that the dehydrator is not workingproperly, and you should check the technical manual forthe solution to the problem.MAINTENANCE OF RECIPROCATINGAIR COMPRESSORSTo keep the ship’s air compressors operatingefficiently at all times, you must know what commontroubles may occur and their causes. You must knowhow to care for the air intakes; how to maintain andreplace air valves; how to take care of air cylinders andpistons; and how to adjust bearings, wrist pins, andcouplings. You must be able to maintain, troubleshoot,and repair the lubrication, cooling, control, and airsystems.AIR INTAKESA supply of clean, cool, dry air is essential to thesatisfactory operation of compressors. To ensure this,the air intake filters must be regularly inspected andcleaned; otherwise, the filter becomes clogged andcauses loss of capacity. A clogged air intake screen orfilter may also cause a compressor to draw oil from itsown crankcase, around rings, or through oil seals,resulting in an explosion.Remove the filter element and clean it with a jet ofhot water or steam, or plunge it into a strong solution ofsal soda. The filter body should be drained and replaced.If the filter is the oil-wetted type, dip it in clean,medium-grade oil and allow it to drain thoroughlybefore replacing the filter in the intake. Do not usegasoline or kerosene for cleaning filters! The fumesmay collect and explode in the compressor or receiver.Take care to prevent entrance of rain or spray intointake pipes, and provide a means for draining the intakepipe of any water that may collect. The lines should beas short and direct as possible.For air compressors used to supply air for the divers,you must prevent the compressor from taking in exhaustgases coming from any internal combustion engines.You must also prevent any possible intake of fumescoming from fuel tank vents, spilled oil, or gasoline.AIR VALVESAir inlet and discharge valves must be kept cleanand in good working order. Leaky valves are generallydirty valves, and they cause capacity loss. The valvesare removed by first loosening their setscrews orclamps, and then removing their cover plates. Eachvalve and valve unloader, if fitted, may then be liftedout. Each valve should be marked to make certain thatit is returned to the same port from which it wasremoved.Valves removed for inspection should not be takenapart for cleaning unless their conditions make itnecessary. Dirt or carbon in valve ports can usually beremoved without taking the valve apart. This is done bysoaking the valves in kerosene, and then giving them astiff brushing or a light scraping. Valve action should betested by inserting a screwdriver through the seat ports;the valve should lift and close freely.If it becomes necessary to disassemble the valve,note the arrangement of the various parts so that theproper relationship will be kept when the valve isreassembled. (Periodic shipboard reports indicatedamage to pistons and associated valve parts frequentlyresults from improperly assembled valves that protrudein the way of the oncoming piston.)Before replacing air valves in a cylinder, inspect thegaskets and replace any that are damaged.Copper-covered asbestos or plain, thin copper gasketsshould be used. If these are not available, 1/16-inchcompressed-asbestos sheet gaskets may be usedtemporarily. Each valve assembly should be inserted inthe same hole from which it was removed. Since it maybe difficult, in many cases, to distinguish betweensuction or discharge valves, extreme care must be takenwhen the valves are being inserted in the cylinder. Makecertain that suction valves open TOWARD, and thedischarge valves AWAY FROM, the center of thecylinder; otherwise, serious damage or loss of capacitywill result. Then place the valve cover on the cylinder,making certain that its gasket is squarely in place; drawdown on the cover nuts evenly, and in turn, so as not totilt the cover. Tighten down the valve setscrew orclamping bolt, drawing it tight to hold the valve on itsseat. If special locknuts are not provided to seal againstleakage at the threads of the valve setscrew, a turn ofsolder or fuse wire should be placed around the screwand set down into a recess by a locking nut.6-8
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