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Psvs Selection Vs Built Up Backpressure

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#1 SawsanAli311


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Posted 05 March 2019 - 12:45 PM

Hi Everyone, 


I have been going through API 520 P1 & P2 codes and I can see that the selection of conventional unbalanced spring loaded PSVs versus the other types of PSVs is mainly focusing on the built up backpressure comparison to the allowable overpressure for the relief contingency. However, we can't ignore the fact that the total backpressure which is the superimposed backpressure (constant + variable) & the built up backpressure plays a role in the PSV performance. 


Other design guidelines state that the selection shall be based on the sum of the variable superimposed and the built up backpressure, in my opinion, variable superimposed would somehow make us think twice before implementing convetnional PSVs.... What do you think?


Can we say that API mainly focused on the built up backpressure portion  since it is mainly driven by the design of the selected tail pipe sizes and since anyways a conventional PSV would not be selected if the superimposed backpressure is highly varying. In other words, knowing the superimposed backpressure being constant, the user can compensate for this value on the test stand of the PSV via the CDTP (cold differential test pressure). 


Appreciate your views on the subject,




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