ENGINEMAN  1  &  C operating   properly   should   be   removed, disassembled, cleaned, and inspected. The disk, or  ball,  and  the  seat  should  be  checked  for pitting and excessive wear. The spring should be carefully  inspected  for  possible  defects.  When  a relief valve is removed for any reason, the spring tension must be reset. Relief  valves  must  never  be  locked  in  the closed position, except in an emergency. When emergency measures are taken, the valves must be repaired or replaced as soon as possible after the  emergency. REDUCING VALVES Reducing valves are used to provide a steady discharge pressure lower than the supply pressure. They are used on gland seal lines, galley steam lines, heating system lines, and on many other reduced-pressure  lines.  A  reducing  valve  can  be set for any desired discharge pressure, within the limits of the design of the valve. After the valve is set, the reduced pressure will be maintained regardless of changes in the supply pressure, as long as the supply pressure is at least as high as the desired delivery pressure. Two types of reducing valves are in common use,  the  spring-loaded  reducing  valve  and  the pneumatic  pressure-controlled  reducing  valve. Reducing valves of the pneumatic type are of two designs—those which regulate low temperature fluids  such  as  water  or  oil,  and  those  which regulate high temperature fluids such as steam or hot water. Spring-Loaded Reducing Valve If  a  spring-loaded  reducing  valve  fails  to operate properly, the trouble may be due to one or 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   proper adjustment of the adjusting spring. 3. Leakage may be caused by failure of the main valve or the auxiliary valve to seat properly. Check the valves for wear and for the presence of dirt or scale. Correct the trouble by cleaning and  grinding-in  the  main  valve  and  the  auxiliary valve. After grinding-in the auxiliary valve, the auxiliary valve stem may be too long. If it is too long, face off the end of the auxiliary valve stem until the proper clearance is obtained between the diaphragm and the end of the valve stem. Pneumatic  Pressure-Controlled Reducing Valve The pneumatic pressure-controlled reducing valve has a water seal in the upper half of the dome and a glycerine seal in the lower half of the dome. 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 the valve has been placed in service. When the valve is being repaired, however, the water seal will probably be lost. Be SURE to replace the water seal before putting the valve back in service, since steam must not be allowed to come in contact with the diaphragm. The glycerine seal does not, as a rule, require replacement in service. However, if it is necessary to replace or replenish the glycerine seal, place the dome in its normal vertical posi- tion and fill it with glycerine to the level of the filling plug. Screw the plug in and tighten it. In an emergency, water may be used temporarily, instead of glycerine, for the lower seal. If a pneumatic pressure-controlled reducing valve   fails   to   operate   properly,   check   the following: 1. If the pressure in the lower dome becomes excessively high soon after the valve has been put into service, the extra pressure may be caused by expansion of the air due to temperature changes. Bleed enough air from the dome so as to main- tain  the  proper  pressure  at  the  operating temperature. 7-34