OPERATING INSTRUCTIONS
MODEL PRS-07i THD
PRESSURE REDUCING VALVE
DISASSEMBLY/ASSEMBLY INSTRUCTIONS
If the regulator fails to maintain the proper outlet pressure,
there could be a number of probable causes as follows: 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 the spring. If this condition appears
frequently a strainer installed at the inlet side of the valve is
recommended. If disassembly is required, make sure the valve
piping is not under pressure and sufficiently cooled off for oper-
ating personnel to handle. To disassemble the valve, it is not
necessary to remove the valve from the piping, although it may
be more convenient to work on the valve at a bench with a vise.
Unscrew the spring chamber (3) with a wrench.
If fluid is leaking from the adjusting screw, the diaphragm is sus-
pect. Inspect the diaphragm (9), replace if torn, abraded, or de-
laminated or otherwise damaged or cut. Sealing area of the
diaphragm should be free from tears or cuts, otherwise external
leakage will occur. Examine to see if there are signs the dia-
phragm pulled away from the outer clamped seating area. If so,
realign diaphragm and make sure the spring chamber is tight-
ened properly, and checked again for tightening after full tem-
perature is reached after installation. Also, check to make sure
the locknut (6) is tight which holds the diaphragm metal plates
together (8) & (10). A spare diaphragm should always be kept
on hand to keep down time to a minimum.
Examine the main valve (12) and seat area for excessive wear
particularly in the valve seat area. If excessive, replace with
new parts. Otherwise, parts may be restored by remachining
and re-lapping with a fine lapping compound, such as 600 or
800 grit. Replace external valve spring (5) if corroded or dam-
aged.
Reassemble valve in the same sequence as disassembled mak-
ing sure the diaphragm lock nut (6) and spring chamber (3) are
tight so that no leakage can take place in these areas. Apply
approximately 45 ft-lbs of torque to tighten the diaphragm lock
nut (6) and approximately 500 ft-lbs to the spring chamber (3).
Also examine the O-ring seal for the bottom plug to make sure it
is not damaged or shows signs of deterioration. Replace if nec-
essary.
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 un-
derside of the diaphragm through a vertical port, which connects
with the outlet port. Pressure regulation is achieved when a force
balance is maintained between 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 by the adjusting spring, the spring force overcomes
the pressure force acting on the underside of the diaphragm. This
causes the main valve to open, thereby admitting higher inlet pres-
sure fluid to raise the outlet pressure until the force balance is re-
stored. As soon as the outlet pressure is restored, the main valve
begins to close and to limit the amount of higher inlet pressure fluid
passing through the valve.
Never apply the valve on shut-off or dead ended service
, as the
valve is not designed for this purpose. Always install a relief valve on
the outlet side of the valve.
OPERATING INSTRUCTIONS
If the valve has not been ordered preset to a specific outlet pressure,
simply adjust the spring (5) compression by loosening the lock nut (2)
and turn the adjusting screw (1)
Clockwise to increase the spring compression. This will increase the
outlet pressure. Similarly, turning the screw counterclockwise will
reduce the spring compression and correspondingly reduce the out-
let pressure.
Phone: 973-340-9955 Fax: 973-340-9933
http://www.straval.com Email: [email protected]
