1 reply to this topic

[millany]

Good day!

i just want to ask for help for anyone who can give information on pilot operated valve.

Im sizing a flare header for butane storage flare. Set pressure of psv in butane storage is only 0.125 barg. It would take a very big size of header to meet a back pressure of 50% (balance type). Im thinking of using a pilot operated valve. Does anyone of you knows the maximum allowable back pressure for pilot operated valve? I initially assume it to be 90% of set pressure. Would that be a realistic assumption? What is the maximum allowable back pressure which is currently avilable in the market for pilot operated valve?

thanks and reagrds!

[gvdlans]

As you probably know, for a pilot operated valve, valve lift is not affected by backpressure. However, since you will have subcritical flow, flow through the valve will be affected by backpressure. So, there are two things happening when you increase maximum backpressure:

1) valve required discharge area increases (in line with equations (3.5)-(3.7) in API RP 520 part I). This required area approaches infinity when relieving pressure approaches maximum backpressure.

2) resulting flare header size decreases

So at some point there will be an economic optimum. Having a maximum backpressure at 90% of set pressure seems a reasonable assumption to me.