ENGINEMAN 1 & Coperating properly should be removed,disassembled, cleaned, and inspected. The disk,or ball, and the seat should be checked forpitting and excessive wear. The spring should becarefully inspected for possible defects. When arelief valve is removed for any reason, the springtension must be reset.Relief valves must never be locked in theclosed position, except in an emergency. Whenemergency measures are taken, the valves mustbe repaired or replaced as soon as possible afterthe emergency.REDUCING VALVESReducing valves are used to provide a steadydischarge pressure lower than the supply pressure.They are used on gland seal lines, galley steamlines, heating system lines, and on many otherreduced-pressure lines. A reducing valve can beset for any desired discharge pressure, within thelimits of the design of the valve. After the valveis set, the reduced pressure will be maintainedregardless of changes in the supply pressure, aslong as the supply pressure is at least as high asthe desired delivery pressure.Two types of reducing valves are in commonuse, the spring-loaded reducing valve and thepneumatic pressure-controlled reducing valve.Reducing valves of the pneumatic type are of twodesigns—those which regulate low temperaturefluids such as water or oil, and those whichregulate high temperature fluids such as steam orhot water.Spring-Loaded ReducingValveIf a spring-loaded reducing valve fails tooperate properly, the trouble may be due to oneor more of the following causes:1. The adjusting spring may have taken a per-manent set. Readjust it or install a new spring.2. The diaphragm may be damaged or ex-cessively deformed. Install a new diaphragm or,if the deformation is slight, make a properadjustment of the adjusting spring.3. Leakage may be caused by failure of themain valve or the auxiliary valve to seat properly.Check the valves for wear and for the presenceof dirt or scale. Correct the trouble by cleaningand grinding-in the main valve and the auxiliaryvalve. After grinding-in the auxiliary valve, theauxiliary valve stem may be too long. If it is toolong, face off the end of the auxiliary valve stemuntil the proper clearance is obtained between thediaphragm and the end of the valve stem.Pneumatic Pressure-ControlledReducing ValveThe pneumatic pressure-controlled reducingvalve has a water seal in the upper half of thedome and a glycerine seal in the lower half of thedome. The glycerine seal is put in at the factory;the water seal is put in when the valve is installed.The condensation of steam is sufficient to main-tain the water seal at the proper level after thevalve has been placed in service. When the valveis being repaired, however, the water seal willprobably be lost. Be SURE to replace the waterseal before putting the valve back in service, sincesteam must not be allowed to come in contact withthe diaphragm. The glycerine seal does not, as arule, require replacement in service. However, ifit is necessary to replace or replenish the glycerineseal, place the dome in its normal vertical posi-tion and fill it with glycerine to the level of thefilling plug. Screw the plug in and tighten it. Inan emergency, water may be used temporarily,instead of glycerine, for the lower seal.If a pneumatic pressure-controlled reducingvalve fails to operate properly, check thefollowing:1. If the pressure in the lower dome becomesexcessively high soon after the valve has been putinto service, the extra pressure may be caused byexpansion of the air due to temperature changes.Bleed enough air from the dome so as to main-tain the proper pressure at the operatingtemperature.7-34
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