Straval PRS-07i THD User manual

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 condion 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 suciently cooled o for oper-
ang 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 uid is leaking from the adjusng 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 seang area. If so,
realign diaphragm and make sure the spring chamber is ght-
ened properly, and checked again for ghtening aer full tem-
perature is reached aer installaon. Also, check to make sure
the locknut (6) is ght which holds the diaphragm metal plates
together (8) & (10). A spare diaphragm should always be kept
on hand to keep down me to a minimum.
Examine the main valve (12) and seat area for excessive wear
parcularly in the valve seat area. If excessive, replace with
new parts. Otherwise, parts may be restored by remachining
and re-lapping with a ne 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
ght so that no leakage can take place in these areas. Apply
approximately 45 -lbs of torque to ghten the diaphragm lock
nut (6) and approximately 500 -lbs to the spring chamber (3).
Also examine the O-ring seal for the boom plug to make sure it
is not damaged or shows signs of deterioraon. Replace if nec-
essary.
PRINCIPLE OF OPERATION
Steam or other uid passing through the valve enters through the
inlet port, through the valve seat formed by main valve and seat, and
nally through the outlet port. Outlet pressure is sensed by the un-
derside of the diaphragm through a vercal port, which connects
with the outlet port. Pressure regulaon is achieved when a force
balance is maintained between the pressure acng on the underside
of the diaphragm and the spring force, which is adjusted to hold a
parcular outlet pressure. If the outlet pressure is below the set
point as preset by the adjusng spring, the spring force overcomes
the pressure force acng on the underside of the diaphragm. This
causes the main valve to open, thereby adming higher inlet pres-
sure uid to raise the outlet pressure unl 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 uid
passing through the valve.
Never apply the valve on shut-o 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 specic outlet pressure,
simply adjust the spring (5) compression by loosening the lock nut (2)
and turn the adjusng 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.
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OPERATING INSTRUCTIONS
MODEL PRS-07i THD
PRESSURE REDUCING VALVE
Phone: [phone] Fax: [phone]
http://www.straval.com Email: [e-mail]
It is oen easier to assemble the spring chamber assembly upside down
by dropping the spring and spring hardware into the spring chamber.
Then the body (13) subassembly with the main valve (12) and diaphragm
(9) can be posioned over the spring chamber (3) and threading the as-
sembly together unl hand ght. Then the nal ghtening with a wrench
can be done with the valve right side up
Aer the valve is properly assembled, reset the spring adjusng screw (1)
unl the desired outlet pressure is achieved at the ow range the valve
will be operang. Then ghten the adjusng screw lock nut (2). Note that
some valves, depending on the droop characterisc, may require read-
justment of the spring seng if there are wide ranges in ows. Consult
factory for applicaon assistance if a dierent spring or if a dierent valve
is required.
NOTE: When the outlet pressure must be maintained
at a specic value, and where excessive pressure may
damage equipment, a relief valve must be installed on
the outlet side of the regulator.