Straval PRS-11 TC User manual

OPERATING INSTRUCTIONS
MODEL PRS-11 TC
SANITARY PRESSURE REDUCING
VALVE
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 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 pressure fluid to raise the outlet pressure until the force
balance is restored. As soon as the outlet pressure is re-
stored, the poppet begins to close and limit the amount of
higher inlet pressure fluid passing through the valve.
Never apply the valve on continuous shut-off or dead
ended service, as the valve is not designed for this purpose.
Install a shut off valve on the inlet to the regulator for pro-
longed periods of shut down. A soft seat such as Teflon or
Viton seat, will improve the shut off characteristics for this
valve compared to a metal-seated valve temporarily. Always
install a relief valve on the outlet of the valve in case
there is a temporary shut-off condition, or if the valve fails to
regulate for any reason, and if there could be a danger of
other equipment failure downstream.
OPERATING INSTRUCTIONS
If the valve has not been ordered preset to a specific out-
let 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 compres-
sion and correspondingly reduce the outlet pressure.
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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, loose gasket materials, 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 on the inlet side of the
valve is recommended. If disassembly is required, make
sure the valve piping is not under pressure and suffi-
ciently cooled off for operating personnel to handle. To
disassemble the valve, it is best to remove the valve
from the piping, by removing the Tri-Clover compatible
flanges. Make sure, there is no pressure on either the
inlet or outlet of the valve. Unscrew the spring chamber
(3) with a large wrench.
If fluid is leaking from the adjusting screw during normal
operation, the diaphragm (10) is suspect. Inspect the
diaphragm, replace if torn, abraded, or delaminated or
otherwise damaged or cut. The sealing area of the dia-
phragm should be free from tears or cuts, otherwise ex-
ternal leakage will occur. Examine to see if there are
signs of the diaphragm being pulled away from the outer
clamped seating area. If so, realign diaphragm and make
sure the spring chamber is tightened properly, and
checked again for tightening after full temperature is
reached after installation. Also, check to make sure the
locknut (7) is tight which holds the diaphragm metal
plates together (9) & (11). A spare diaphragm should
always be kept on hand to keep down time to a mini-
mum.
Examine the main valve seat (13) and seat area of the
body for excessive wear. If excessive, replace with new
parts.
The main valve assembly needs to be disassembled if the
seat needs to be replaced. This is performed by applying
two wrenches on the wrench flats provided on each end
of the main valve. Replace external valve spring (5) if
corroded or damaged.
Reassemble valve in the same sequence as disassembled
making sure the diaphragm lock nut (7) and spring
chamber (3) are tight so that no leakage can take place
in these areas. Apply approximately 125 IN-LBS of
torque to tighten the diaphragm lock nut (7) and approx-
imately 600 IN-LBS to the spring chamber as it gets
threaded on to the body (12).
After the valve is properly assembled and tight, the valve
is ready for installation, or bench test, off line. This can
be done with air or water. This can be done with air or
water. The proper Tri-Clover flanges will be required in
order to make the connection to the inlet and outlet of
the valve.
DISASSEMBLY/ASSEMBLY INSTRUCTIONS

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A minimum pressure source of about 85 to 100 psi is usually
sufficient on the inlet side if the maximum outlet pressure of
75 psi needs to be set. If not, supply the same pressure as will
exist as the line pressure in the process. On the outlet side of
the piping install a stop valve with a tee and pressure gauge in
order to measure the outlet pressure.
Next, back out the adjusting screw (1) until there is no spring
(5) compression. Make sure the stop valve on the outlet is
closed. Now apply inlet pressure to the valve. If the valve seat
(13) is holding properly, there should only be a minimal pres-
sure reading on the outlet usually from 5-25 psi depending on
the specific valve. This pressure reading should stay constant
until the adjusting screw is screwed in to compress the adjust-
ing spring further. As the adjusting screw is threaded in more
and more, the pressure should begin to rise gradually on the
outlet until the maximum is reached. A good valve seat will
hold the pressure at each setting, without letting it build up
rapidly. A poor seat, or one that is worn, will let the pressure
rise almost immediately, even with the adjusting screw backed
out all the way. Another indication of poor seat leakage could
be if the main valve is not free to move freely, which could be
from debris or wear, which should have been discovered during
the disassembly process discussed above.
If the valve tests satisfactorily with pressure increasing, it is
ordinarily not necessary to test the valve in the opposite direc-
tion, as the valve will usually perform well at this stage. How-
ever, if desired, reducing the outlet pressure is done by, back-
ing the adjusting screw out incrementally. But each time this is
done, the higher pressure on the outlet reached from the pre-
vious test needs to be vented by opening the shut off valve on
the outlet, and then immediately closing it to see if the new
reduced pressure holds. This can be repeated several times
until the minimum pressure setting is reached after the valve is
bench tested, reset the spring adjusting screw (1) until the
desired outlet pressure is achieved at the flow range the valve
will be operating. Then tighten the adjusting screw lock nut
(2). Note that some valves, depending on the droop character-
istic, may require readjustment of the spring setting if there
are wide ranges in flows or large changes in inlet pressures.
OPERATING INSTRUCTIONS
MODEL PRS-11 TC
SANITARY PRESSURE REDUCING
VALVE