The PRP valve case is provided with shock mounts and
with the direction-of-flow arrow pointing toward the
PRP. Since the PRP manifold contains only six ports for
brackets for fastening to a bulkhead.
transmission tubing connection, systems requiring
The operating mechanism consists of a spring-
seven or more HSDs will Tee together vented check
loaded operating lever operated by a release diaphragm
valves, starting with the seventh check valve. The
check valves prevent the rapid increase in air pressure
release diaphragm is connected to the tubing from the
created in an individual HSD from pressurizing the
HSDs. The front of the release diaphragm is open to the
entire system. The check valve body contains a vent
interior of the PRP valve case. When the PRP valve is
installed in a bypass around the main valve. The vent
set, the operating lever is cocked to hold the valve
permits a slow backflow of air to equalize system
closed. A sudden or gradual increase in pressure
pressure in response to normal changes in ambient
transmitted from one or more HSDs will move the
diaphragm, releasing the operating lever. As the
Pneumatically Released Pilot (PRP) Valve
operating lever moves, it causes the seat holder to move
away from the seat, thereby permitting seawater to enter
the hydraulic control system piping and actuate the
spring-loaded pilot valve that opens automatically to
actuate the magazine sprinkler system in response to a
The PRP valve is equipped with a compensating
pneumatic signal from one or more thermopneumatic
vent that leaks off the slight increases or decreases of
pressure within the HSDs caused by normal
The main components of the PRP valve are the
temperature fluctuations in the protected compartment.
operating mechanism, the compensating vent, and the
This leakoff of slow pressure changes equalizes the
pilot valve. The operating mechanism and the
pressure on both sides of the release diaphragm and
compensating vent are housed in a circular bronze case.
prevents inadvertent tripping of the PRP valve. The
The pilot valve is mounted on the front of the case and is
compensating vent is calibrated at the factory and
installed in a 3/8-inch line that connects the firemain to
the sprinkler system hydraulic control system piping.
should not be adjusted by ship's force.
Figure 1-7.--Pneumatically released pilot (PRP) valve.