Dear All,
I have a pressure control valve with a bypass globe valve venting into LP flare header.
Control valve failure open is critical factor for LP flare sizing. Control valve failure open load is calculated at PAHH of upstream vessel.
There is a proposal to limit Cv of control valve in order to limit total max flow through both control valve and bypass valve at xx kg/h.
What note should we specify correctly to vendor ?
Option 1: Limit Cv of control valve to limit max flow through control valve at xx/2 kg/h. (a division factor 2 is used as failure open considers both control valve and by pass valve).
Option 2:same as option 1 with indicating upstream pressure: xx barg corresponding to PAHH and outlet pressure: yy barg.
Please advise which option is more appropriate and why ?
Regards.