OPERATING INSTRUCTIONS
MODEL PRH-09THD
PRESSURE REDUCING VALVE
APPLICATIONS:
Valve should only be used for non-corrosive fluids, or where
the materials selected are compatible with the fluid and will
not cause corrosive buildup, which could keep the main
valve from opening. When liquids contain debris or other
solid matter, which might cause internal clogging or improp-
er operation of the valve, a strainer with a fine wire mesh
should be installed before the inlet of the valve. In-line
strainer fittings or basket strainers can be purchased from
STRA-VAL to solve this problem.
Do not use this valve as
a shutoff valve
, even though the valve, when new, is able
to do so. In time as wear sets in, seat leakage may increase
and result in an objectionable pressure rise at zero flow. As
long as the flow through the valve is greater than the seat
leakage, the valve could still regulate.
PRINCIPLE OF OPERATION
Phone: 973-340-9955 Fax: 973-340-9933
http://www.straval.com Email: [email protected]
When the valve is shipped from the factory it is usual-
ly ready for operation. On larger valves, all that may
be required is to install the adjusting screw if it is
strapped to the spring chamber and make a final pres-
sure adjustment at the final operating conditions. This
step is not required if the valve is ordered preset for a
specific pressure setting and so marked
Check to make sure that the discharge piping is not
blocked off and that the valve does not operate
against a shut-off condition. Check to make sure there
is no visible leakage coming from the spring chamber.
This would occur if the packing nut is set too loose or
if the packing rings take a slight set. A simple adjust-
ment of the packing nut by 1/6 or 1/4 turn is normally
sufficient. This would have to be done with the spring
chamber removed If after extensive use the valve be-
gins to lose its ability to regulate, or if there is exces-
sive seat leakage due to wear, which would cause an
excessive pressure rise on the outlet side of the
valve, or if there is external seal leakage, the valve
will require parts to be replaced and
the valve sent in for possible repair. Before removing
the valve from service
Make sure that the valve is
isolated from the piping completely in order
avoid any personal injury
Usually, only the v-packing rings will require replace-
ment. However, if there is excessive seat leakage,
then the main valve may also require replacement or
just a minor re-cutting of the seating surfaces. With
the valve removed from service, a quick test for me-
chanical operation is to see if the
main valve is free
to move by hand
. This should be done with the
spring chamber removed. If the main valve is
not
free
to move,
the packing nut is either too tight
or the
main valve is frozen in place or worn, and will there-
fore need to be disassembled.
MAINTENANCE & REPAIR
Fluid passing through the valve enters through the inlet port
through the valve seat formed by the main valve and seat,
and finally through the outlet port. Outlet pressure is sensed
by the underside of the piston, which is able to move up and
down with changes in outlet pressure. Pressure regulation is
achieved when a force balance is maintained between the
pressure acting on the underside of the piston and the
spring force, which is adjusted to hold a particular outlet
pressure. If the outlet pressure is below the set point,
which is preset by the adjusting spring, the spring force
overcomes the pressure force acting on the underside of the
piston. This causes the main valve to open, thereby admit-
ting higher inlet pressure fluid to raise the outlet pressure
until the force balance is restored. As soon as the outlet
pressure is restored, the main valve begins to close to limit
the amount of higher inlet pressure fluid passing through
the valve
DISASSEMBLY / ASSEMBLY INSTRUCTIONS
To disassemble the valve, it is best to remove the
valve from the piping, since it is more convenient to
work on the valve on a bench with a vise. Unscrew
the spring chamber with a wrench in the area provided
with wrench flats. With the spring chamber off, the
packing nut may be removed and the Teflon v-packing
rings extracted. Make sure the valve is not under
pressure if it is still in the line. Be sure not to damage
them as they perform a critical sealing function. If
they are damaged or worn they need to be replaced.
When reinstalling the v-packing rings, make sure that
they are properly installed as shown in the illustration
with the open part of the “v” facing the pressure side.
