Maximum flow through 100% open valve
Maximum flow through 100% open valve
(OP)
Hi Everyone,
I'm having a brain fart and can't remember how to calculate max. flow through a valve for PSV sizing purposes. I have a superheated steam line with pressure reducing valve:
Inlet and Outlet Line size: 3"
Valve size: 3"
Pinlet = 190 psig
Poutlet= 73 psig
Tinlet = 275C
Flow = 700 #/hr.
My downstream piping pressure rating is 150 psig. So I need to calculate flow through this valve fully open and deduct 700#/hr flow in order to find out what required capacity of PSV. Am I correct? How to calculate this maximum flow?
Thanks,
Curtis
I'm having a brain fart and can't remember how to calculate max. flow through a valve for PSV sizing purposes. I have a superheated steam line with pressure reducing valve:
Inlet and Outlet Line size: 3"
Valve size: 3"
Pinlet = 190 psig
Poutlet= 73 psig
Tinlet = 275C
Flow = 700 #/hr.
My downstream piping pressure rating is 150 psig. So I need to calculate flow through this valve fully open and deduct 700#/hr flow in order to find out what required capacity of PSV. Am I correct? How to calculate this maximum flow?
Thanks,
Curtis





RE: Maximum flow through 100% open valve
The valve's sizing sheet doesn't have selected valve's Cv. It only lists required Cv at given flow. Selected valve is T-Globe valve.
Do we need Cv at 100% open position to calculate max flow?
Thanks,
Curtis
RE: Maximum flow through 100% open valve
you can only remove the 700 lbs/hr if the flow is somehow 100% guaranteed while your regulating valve goes 100% open?
Even if its just running at say 300lb/hr rather than isolated, this will impact on your relief valve capacity
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Maximum flow through 100% open valve
If you can get the Cv then its easy: Cv=Q*sqrt(SG/dP) for a liquid. If you are dealing with a gas its a little more complicated...
Best regards, Morten
RE: Maximum flow through 100% open valve
But the max pressure in the remainder of the line is the 70 psig, right? So the LP relief setting has to be based on the desired 7- psig, but is a separate relief valve required for the higher pressure part of the line since the orifice cannot "fail" ?
RE: Maximum flow through 100% open valve
Just to give you more details of my system. I have auxiliary system, which required a constant flow of 700# steam at 73 psig. This flow is guaranteed and consumed by steam ejectors. This system is fed from another steam source with 190 psig pressure a through pressure control valve (T-globe type valve).
This auxiliary system has a pressure vessels and components with MAWP of 150 psig and supplied with a PSV. I'm trying to get answers from supplier about PSV valve supplied with the system. However, it seems she doesn't have a clue why they supplied this PSV and how do they sized it.
I think, think this PSV shall be sized for the T-globe fail 100% open. In case is T-globe valve fails and opens at 100%, PSV shall be able to remove flow and keep a pressure under 150 psig.
I think, there shall be a formulae for calculating a flow through a valve with 100% open Cv, P1 = 190 psig and P2 = 150 psig, which gives us bases for sizing of PSV. However, I have checked T-globe valve sizing sheet and it doesn't have Cv100% value for the valve selected. I guess, I have to go back to the T-globe valve supplier and get Cv100% for the valve.
Do you know what formulae shall I use for calculation of flow through 100% open valve?
Thanks,
Curtis
RE: Maximum flow through 100% open valve
Remember that your relieving pressure is 1.1*SP if the valve is an API 520 valve
RE: Maximum flow through 100% open valve
Worth finding out what the flow through your d/s system is at 150 psi before you go and put in a relief valve that might not be required.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Maximum flow through 100% open valve