OPERATING INSTRUCTIONS
MODEL PRS-05 THD
PRESSURE REDUCING VALVE
DISASSEMBLY/ASSEMBLY INSTRUCTIONS:
If the regulator fails to maintain the proper outlet pres-
sure, there could be a number of probable causes as fol-
lows: internal clogging of foreign objects or material,
sediment, rust, etc. In the valve seat area, sensing port,
diaphragm cavity and valve spring cavity which houses
spring. If this condition appears frequently a strainer in-
stalled at the inlet side of the valve is recommended.
PRINCIPLE OF OPERATION
Steam or other fluid passing through the valve enters through
the inlet port, through the valve seat formed by main valve
and seat and finally through the outlet port. Outlet pressure
is sensed by the underside of the diaphragm through a verti-
cal port, which connects with the outlet port. Pressure regu-
lation is achieved when a force balance is maintained be-
tween the pressure acting on the underside of the diaphragm
and the spring force, which is adjusted to hold a particular
outlet pressure. If the outlet pressure is below the set point
as preset bye the adjusting spring the spring force overcomes
the pressure force acting on the underside of the diaphragm,
which causes the main valve to open thereby admitting high-
er 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.
OPERATING INSTRUCTIONS
If the valve has not been ordered preset to a specific outlet
pressure, simply adjust the spring compression by loosening
the lock nut and turn the adjusting screw
clockwise to increase the spring compression. This will in-
crease the outlet pressure. Similarly, turning the screw coun-
terclockwise will reduce the spring compression and corre-
spondingly reduce the outlet pressure.
Phone: 973-340-9955 Fax: 973-340-9933
http://www.straval.com Email: [email protected]
If disassembly is required make sure the valve piping is
not under pressure and sufficiently cooled of for operat-
ing personnel to handle. To disassemble the valve, it is
not necessary to remove the valve from the piping, alt-
hough it may be more convenient to work on the valve
on a bench with a vise. Unscrew the spring chamber
with a wrench.
Inspect the diaphragm 12), replace if corroded or de-
formed. Sealing area of the diaphragm should be free
from nicks or other indentations otherwise external leak-
age could occur. No gasket is otherwise required in this
area. If excessive permanent deformation exists in the
diaphragm, this could be an indication that the outlet
pressure is too high for the rated pressure of the dia-
phragm. A thicker diaphragm may be required for the
particular service used. Another reason could be that the
valve seat or the static seal between the seat (8) and the
body (10) is not effective. This could be from corrosion,
or simply that the seat has not been screwed in tight
enough for a metal seal to occur.
Examine the main valve and seat for excessive wear par-
ticularly in the valve seat area. If excessive replace with
new parts, otherwise parts may be restored by re-
machining and re-lapping with a fine lapping compound
such as 600 or 800 grit. Replace internal valve spring if
corroded.
Reassemble valve in the same sequence, as disassem-
bled, making sure the seat has been screwed in very
tight. Before reassembling the spring chamber and re-
lated parts, check for the proper protrusion of the main
valve above the seat as shown in the illustration below.
The proper gap between the underside of the diaphragm
and top of the valve stem should be as indicated in the
diagram. This can be checked with an accurate straight
edge and a feeler gauge. If the valve stem protrudes too
far above, remove the excess by ringing or filing until the
proper gap is achieved.
NOTE:
When the outlet pressure must be main-
tained at a specific value where excessive pressure
may damage equipment, a relief valve must be in-
stalled on the outlet side of the regulator.
