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
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
designsthose which regulate low temperature
fluids such as water or oil, and those which
regulate high temperature fluids such as steam or
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.
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
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