real flow for a psv
real flow for a psv
(OP)
a question for you guys:if i have a PSV installed (for whatever reason) and it opens ¿what is the flow trough this valve? ¿is the one calculated by a contingency (fire for example)? or ¿is the calculated by the actual orifice with the upstream pressure ?(assuming critical flow).
thanks for the help
thanks for the help





RE: real flow for a psv
The only flow you are guaranteed of achieving is the flow stamped on the PSV. This is called the stamped or rated flow and is based on flow at a 10% over pressure; this of course implies the actual orifice. Again, there has been debate on whether you will ever really achieve this flow in a typical spring loaded, pop-open action relief valve but it has been reafirmed by API in interpretations that one must use the rated (stamped) flow in calculations for the PSV inlet and outlet piping.
RE: real flow for a psv
Good luck,
Latexman
RE: real flow for a psv
pleckner you are rigth, it is a gas /vapor relief (i forgot to mention it).
I asume that for a multiple valve scenario is the same for each valve: discharging the flow calculated in this way.
In the API 521 is not very clear if you can use the contingency flow or the actual flow. Obiously for design you use the contingency flow but for an evaluation of an existing system, should i use the actual flow?.
thanks again
RE: real flow for a psv
You determine the PSV inlet and outlet size, the inlet design (< 3% of set pressure), and the outlet design and PSV type (conventional, bellows, or pilot operated) using the actual flow of the overall worst condition.
Good luck,
Latexman
RE: real flow for a psv
RE: real flow for a psv
RE: real flow for a psv
best regards
RE: real flow for a psv
I already responded to what API RP521 has to say about which flow to use for the tail pipe (use rated capacity, NOT required capacity) and for the header (use rated capacity for a single discharging valve, use the worst-case cumulative REQUIRED capacities of ALL devices that may reasonably be expected to discharge simultaneously during a given relief scenario.) So to give you another opinion, you will need to indicate where in API RP521 you are referring to.
RE: real flow for a psv
That is why a asked your opinion about use rated capacity in a multiple valve scenario.
best regard
RE: real flow for a psv
Good luck,
Latexman
RE: real flow for a psv
Code, Section VIII, Division I, Appendix M-8.)" as saying one needs to conisider that you should not be using the REQUIRED relieving rate of these simultaneously releasing PSVs but you may have to use the RATED flow for all valves relieving.
It still boils down to using either required relieving rates or the rated flows. A fire scenario or other external heating source would be an excellent example of when we should consider using the full RATED flow from each PSV and not the required relieving flows. Why would the valves NOT pass the rated flow in these scenarios? I can't think of any reason they would not.