OPERATING INSTRUCTIONS
MODEL RVC-05 THD
PRESSURE RELIEF VALVE
Another reason for replacing or repairing a valve is if
there is excessive leakage from the valve seat. If this
happens even with the spring compressed to the max-
imum (this should only be temporarily done for test
purposes), this is an indication the poppet and or
valve seat on the body is worn, damaged, corroded, or
a particle lodged in the seat causing the valve to con-
stantly leak. If leakage is observed through the spring
adjusting screw, this indicates there is leakage in the
piston seal, which requires replacement.
This would be observed only while the valve is dis-
charging and there is some pressure on the outlet side
of the valve. Ordinarily this is not a major problem as
the discharge is usually piped to atmosphere and little
or no back pressure exists unless the valve is fully dis-
APPLICATIONS: charging.
Valve should only be used for non-corrosive, non-adhesive flu-
ids, or where the materials selected are compatible with the flu-
id and will not cause corrosive buildup, which could cause stick-
ing or keep the poppet from opening. When liquids contain de-
bris or other solid matter, which also might cause internal clog-
ging or improper operation of the valve, a strainer with a fine
wire mesh should be installed before the inlet of the valve. Bas-
ket strainers or filters can be purchased from STRAVAL to solve
this problem. Any problematic fluids that may cause the valve to
work improperly will periodic testing and possible frequent flush-
ing.
PRINCIPLE OF OPERATION
This is a poppet and spring type relief valve where the spring
constantly opposes the pressure acting against the poppet,
which seals of the inlet port from the outlet port at the valve
seat. The desired set pressure or relief is achieved by compress-
ing the spring until the spring force is adequate to balance the
pressure force acting against the poppet. When the inlet pres-
sure exceeds the set pressure, the poppet will open to relieve
the excess pressure .
MAINTENANCE & REPAIR
The valve should be periodically checked for proper operation.
This can be easily done by reducing the spring compression from
its current pressure setting.
Eventually the poppet must open and begin to discharge liquid or
gas under pressure. Make sure that the discharge is proper-
ly piped to a safe area in order avoid any personal injury.
Before reducing the pressure, a simple measurement of the ad-
justing screw height will make it easier to reset the pressure to
its original setting if the pressure cannot be easily measured.
If the poppet fails to open with the adjusting screw sufficiently
backed out and the valve is under pressure, the poppet is proba-
bly frozen or corroded in place. If this condition exists, the valve
must be immediately removed from service and replaced or
repaired.
Phone: 973-340-9955 Fax: 973-340-9933
http://www.straval.com Email: sales@straval.com
OPERATING INSTRUCTIONS
PROCEDURE FOR DISASSEMBLY MODEL RVC-05 THD
Make sure the valve is isolated and is not under pressure. Next
remove the valve from the system. Back out the spring adjusting PRESSURE RELIEF VALVE
screw until there is no longer any spring compression. It may also
be removed completely if desired. Unscrew the spring chamber
using the flats provided on top of the spring chamber. At the proper system over pressure, turn the adjusting
Now the top of the poppet is exposed. While still assembled, test screw until the valve begins to open. Next reduce the
to see if the poppet is free to move by hand. There should only be system pressure to the normal operating pressure and
a slight resistance to movement resulting from the O-ring friction check to see if the valve reseats properly and shuts off.
between the piston and the body. The piston can now be pulled If it is not possible to change the system pressure to an
out through the top of the body. Examine the O-ring or seal to overpressure condition, at which point the valve must
see if any deterioration has taken place and replace if necessary. open, then the valve must be tested and set off line us-
Next examine the poppet seating surface where it contacts the ing a hydrostatic testing device.
body and the mating surface on the body. Usually if there is se-
vere leakage, the condition of theses seating surfaces will indicate IMPORTANT NOTE FOR SOCKET WELD
a worn or deteriorated surface finish. If the seat leakage is only
minor, a re-lapping procedure using a #600 lapping compound CONNECTIONS:
will usually solve the problem. When socket welded connections are ordered, remove the
Examine the body bore where the piston or poppet is housed. If poppet from the body during welding of the pipe in order
the surface is not smooth, the bore should be polished with a to prevent burning of the elastomeric seal. Use minimum
very fine abrasive paper or fine scotch brite. The same should be heat during welding. Valve may require re-lapping after
done with the piston or poppet outside diameter. These opera- distortion caused by welding. Also, check to make sure
tions can be done in a small lathe. Use extreme caution when the piston is free to move without binding or sticking.
polishing the body so as not to get a finger caught in the dis- There should only be a slight resistance resulting from
charge port if the body is rotating in a lathe while polishing. If friction of the seal against the body bore.
the valve body and poppet require re-machining from extreme
wear or corrosion, use only an experienced tool room machinist
to perform this operation on a precision lathe, as the parts must
be completely concentric to within .001 TIR. If this is not done
properly, the valve will not seat properly and it may not even be
possible to lap the valve in. If the bore requires re-machining,
there is a risk that too much clearance will result in the seat not
closing properly because of excessive side movement. Ordinarily
the side clearance between the piston and body bore should only
be about 0.001 to 0.0025 in depending on the size. Consult facto-
ry for proper clearances for your specific valve.
If the valve is severely damaged and if it is not practical to re-
machine because side clearances would be excessive, then a new
valve should be purchased, or the valve shipped to STRAVAL for a
repair evaluation and possible repair or replacement.
Don’t forget to examine the adjusting spring to look for signs of
corrosion or outright failure. Replace if necessary. Springs are
usually always in stock at STRAVAL and can be readily shipped.
REASEMBLY & TEST
When all the valve parts are cleaned and inspected, the valve can
be reassembled in reverse order.
Make sure a valve seal lubricant is used to lubricate the seal and
is compatible with the ELASTOMER used.
Make sure no dirt or foreign particles are embedded in the valve
seat, which might cause the valve seat to stay partially open and
cause unwanted leakage.
When the spring and spring hardware is assembled and the
spring chamber threaded on to the body tightly, the valve is
ready for final installation and test.
Testing should be done with the valve completely piped up with
the discharged piped safely away.
Phone: 973-340-9955 Fax: 973-340-9933
http://www.straval.com Email: sales@straval.com
