Calculate flow through a globe valve when Cv and maximum upstream pressure is known

[johcatrac]

Folks,

How do I calculate the flow through a fully open globe valve when Cv and maximum upstream pressure is known? Any tips would be welcome. The pipe and valve is 1" NPS and also for this case, since I am sizing a relief valve, I will be ignoring pipe friction.


Thank you.

 

[MFJewell]

Q=Cv*sqrt(dP/SG)

 

[johcatrac]

The issue in the formula is the dP or is it not, as pressure drop increases with flow rate?

 

[LittleInch]

Or to put it another way, the flow rate Q varies (increases) with varying ( increasing) Differential pressure.

Be warned that at some point you might hit choked flow at which point if upstream pressure and density are fixed then mass flow rate cannot increase further. for gases if the ratio of absolute pressures is around 0.5 to 0.6 then you get choked flow. Liquids are a bit more complex as it involves vapour pressure and other factors.



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