Pressure relief valve

[wookiyo]

according to api 676, rotary type pump.
Why the relief valves that are integral with or internal to
the pump are not acceptable?
It can be sufficient only with external relief valve to protect equipment or piping system?


Thanks in advance,

 

[TD2K]

It's a client preference. Some allow credit for the integral relief valve, some don't, some will in some cases in my experience.

External relief valves are easier to remove and have a spare installed compared to having to send the pump to the shop. They can also be ASME certified, I doubt (but don't know) that's true for an integral relief valve. It may also not be easy for a PSV shop to be able to hook up a supply pressure pump to verify the cracking pressure for an integral PSV compared to the equipment they already have for checking conventional PSVs.

 

[Montemayor]

TD2K:

You are absolutely right. To my knowledge, this type of integral relief valve is not certified by ASME.

I have worked on quite a few DuPont projects in the past where this issue came up and the simple answer is: Don't use or depend on this type of PSV. I have since applauded DuPont's stance of not accepting a relief device that is frankly not backed up by calculations or any engineering tests. DuPont did (to my knowledge) extensive field work in researching and looking into the amount of serious engineering calculations and experimental work done on these PSVs by the pump manufacturers and the truth that came out was that there was none in every case looked at. Therefore, the obvious and practical engineering resolution is: do not rely on this type of device. You are not backed up by credible engineering work. Always insist on an external, certified PSV fully backed up by documentation and expert manufacturer.

 

[bingopin]

Lots of good reasons mentioned on why you would include a "real" PRV in the piping system and my reasons are similar:
Testing them can be problematic.
The pump manufacturers know little about them, provide almost no documentation on them, and really aren't interested in them.
They are frequently "messed" with when someone is troubleshooting pump performance i.e. they are not treated like "real" prv's.
Sometimes they have plastic bodies or other plastic components.
We've learned that it is nearly impossible to manage integral relief valves...there usually is no data sheet or test records.

The only place I would consider depending on an integral PRV would be utility service when the consequence of failure was minimal.

 

[jet1749]

Integral relief valves are for short term pump protection. External relief valves are for process and safety protection. Integral relief valves direct the process product back to the suction side of the pump, this increases the temperature of the pumpage and if the situation continues can lead to pump damage/fires etc. some positive displacement pump manufacturers have now dispensed with the integral device, and recommend an external relief valve that discharges back to the source of the feed (supply tank)