Relief Valve lifting low in field, lifts normally on test bench
Relief Valve lifting low in field, lifts normally on test bench
(OP)
Hi all,
We have an ongoing problem with a relief valve. On the discharge side of a pump (water, ambient temps), we have a relief valve that has repeatedly lifted prematurely. When removed and bench tested, this relief valve will then lift within 1% of the 235psig setpoint. Upon reinstallation in the system, it again lifts early. This indicates a problem with the system - not the relief valve.
We've thoroughly reviewed the calculations for this piping system and components, and we know from local pressure gauges that pressure does not approach 235 psig. Are there any suggestions as to what could be causing this? Could local pressure be higher than system pressure (i.e. a standing wave in the relief valve inlet piping)?
Thanks for the help!
We have an ongoing problem with a relief valve. On the discharge side of a pump (water, ambient temps), we have a relief valve that has repeatedly lifted prematurely. When removed and bench tested, this relief valve will then lift within 1% of the 235psig setpoint. Upon reinstallation in the system, it again lifts early. This indicates a problem with the system - not the relief valve.
We've thoroughly reviewed the calculations for this piping system and components, and we know from local pressure gauges that pressure does not approach 235 psig. Are there any suggestions as to what could be causing this? Could local pressure be higher than system pressure (i.e. a standing wave in the relief valve inlet piping)?
Thanks for the help!





RE: Relief Valve lifting low in field, lifts normally on test bench
RE: Relief Valve lifting low in field, lifts normally on test bench
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
RE: Relief Valve lifting low in field, lifts normally on test bench
It lifts during continuous operation.
Additionally: Some people here questioned the effect of nozzle loading on PSV set points. But we've checked fit-up by unbolting the flanges and the piping aligns nicely and bolts together smoothly.
Also, we've installed a different PSV (same make/model) into this location, and it had the same failure (but it too passed the bench test)!
The operating pressure of this system is around 160 psig. Local, calibrated gauges read this pressure when the PSV is lifting.
This problem really has me thinking!
RE: Relief Valve lifting low in field, lifts normally on test bench
I suppose a reciprocating pump could cause a similar effect - where the average pressure is well below the set point but very short lived spikes could lift the valves.
The million dollar question is "why put a relief valve there in the first place?". What are you trying to protect against on a pump discharging to atmosphere? Perhaps this will give us a clue.
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"An undefined problem has an infinite number of solutions"
RE: Relief Valve lifting low in field, lifts normally on test bench
Was the pressure gauge on the test bench verified? Probably was.
Is the PSV installation on the vertical-up, center branch run of a Tee so it sees a good static pressure?
Good luck,
Latexman
RE: Relief Valve lifting low in field, lifts normally on test bench
Type of pump, type of PSV distance between PSV and pump disch, velocity off the pump.
Give us a picture.
What would you be doing, if you knew that you could not fail?
RE: Relief Valve lifting low in field, lifts normally on test bench
David
RE: Relief Valve lifting low in field, lifts normally on test bench
So, if any pressure spike opens the PSV, it can't close (reseat).
Look for pressure spikes. Is it a PD pump? What kind of pump?
Good luck,
Latexman
RE: Relief Valve lifting low in field, lifts normally on test bench
Good luck,
Latexman
RE: Relief Valve lifting low in field, lifts normally on test bench
RE: Relief Valve lifting low in field, lifts normally on test bench
I'll be looking more closely into the possibility of a pressure spike from the pump, air entrapment, and valve closure.
The pump is centrifugal. 10" discharge pipe, 3000gpm, 12ft/s. There is a downstream check valve, and then a vertical tap off for this relief valve.
RE: Relief Valve lifting low in field, lifts normally on test bench
What would you be doing, if you knew that you could not fail?
RE: Relief Valve lifting low in field, lifts normally on test bench
David