Straval PRS-05 THD Operating Instructions Manual

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 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 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 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.

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 in­crease the outlet pressure. Similarly, turning the screw coun­terclockwise will reduce the spring compression and corre­spondingly reduce the outlet pressure.

OPERATING INSTRUCTIONS

MODEL PRS-05 THD

PRESSURE REDUCING VALVE

If disassembly is required make sure the valve piping is
not under pressure and sufficiently cooled of for operat­ing 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
on a bench with a vise. Unscrew the spring chamber
with a wrench.

Inspect the diaphragm 12), replace if corroded or de­formed. Sealing area of the diaphragm should be free
from nicks or other indentations otherwise external leak­age 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 dia­phragm. 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 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 internal valve spring if
corroded.

Reassemble valve in the same sequence, as disassem­bled, making sure the seat has been screwed in very
tight. Before reassembling the spring chamber and re­lated 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 main­tained at a specic value where excessive pressure
may damage equipment, a relief valve must be in­stalled on the outlet side of the regulator.

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
spring. If this condition appears frequently a strainer in­stalled at the inlet side of the valve is recommended.

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Reassemble the spring chamber making sure the diaphragm is
properly located in its counterbore diameter in the spring cham­ber, otherwise proper sealing is not achieved. One technique to
make sure the diaphragm stays seated in the spring chamber
counterbore during assembly is to place the spring chamber up­side down with gravity keeping the spring hardware in place. The
body also in the upside down position can now be carefully
screwed into the spring chamber with the diaphragm properly
located. The spring chamber must be tightened with an adequate
sized wrench and tightened securely to achieve an adequate met­al seal. If leakage occurs, retighten the spring chamber until the
leakage stops. If leakage still persists and the diaphragm is
properly seated, the only possibility left is a damaged seating
surface on the body such as scratches or nicks, or scratches or
defects in the diaphragm seating surface area.

After the valve is properly assembled, reset the adjusting screw
until the desired outlet pressure is achieved at the flow rage the
valve will be operating, then tighten the adjusting screw lock nut.
Note that some valves depending on the droop characteristic may
require readjustment of the spring setting for wide ranges in
flows, or where large changes in inlet pressure occur. Consult
factory for application assistance if a different valve is required.

OPERATING INSTRUCTIONS

MODEL PRS-05 THD

PRESSURE REDUCING VALVE

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