What is the exact definition for CV valve?

Does it means the definition for Cv with respect to a valve's capacity.

The Cv is the number of US gallons of water the valve will pass with a differential pressure of 1 psi.

The standard equation for a valve's capacity in liquid service is:

Q = Cv(dP/SG)^0.5

This assumes there is no flashing or cavitation of the fluid.

Q is the flowrate, gpm
Cv is the valve Cv
dP is the differential pressure, psi
SG is the specific gravity of the fluid

The process of determining the Cv value of a valve is quite impoortant... temp. must remain constant, valve should be tested between 5-15 psid, etc.  The Cv value is, to my belief, useless as a tool beyond a convenient number to compare valves.

Check into ISA standards, ISA-S75.02.

Other values(Balance Valves) such as loss coefficeint may provide a more accurate tool but for most engineering purposes Cv will do all right.

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