Cv is the capacity of a valve and is defined as :
“No of gallons per minute of water which passes through a fully open valve at a pressure drop of 1 psi.”
CV = q ( ▲P / G )
Cv = Valve co-efficient
q = Volumetric flow rate ( gallons minute )
▲P = Pressure drop across the valve in psi.
G = Specific gravity of flowing fluid.
The valve coefficient Cv is proportional to the area ‘A’ between the plug and valve seat measured perpendicularly to the direction of flow.