Control valve flow coefficient Cv and Kv
|Formula||The flow through a valve can be calculated thanks to the
pressure drop through the valve and a coefficient Kv which
represents the number of m3/h of water that goes through the
valve at 15c and with a pressure drop of 1 bar.
Manufacturers may specified the coefficient Cv instead of Kv for their valve. Cv is the number of US gallons that goes through the valve at 60F and with a pressure drop of 1 psi. It is actually possible to Kv and Cv and have the expression in the right unit for the calculation of interest. Cv=1.156Kv
Note that these formula are only valid with Newtonian liquids.
|Nomenclature||Qv=Flow rate (m3/h)
Cv=valve flow coefficient (GPM)
Kv=valve flow coefficient (m3/h
ΔP=Pressure drop accross the valve (bar)
d15t=density of the liquid referred to water at 15 degrees (-)
|Usual values||In order to have a good control, the design of the control valve should be such that it represents around 1/3 of the total pressure drop of the line. The valve must also be designed to work at flows corresponding to 50 to 80 percent of the Cv of the valve.|
|Other relations||The flow through the valve can be directly expressed with Cv
in US units
With ΔP in Psi, Qvin GPM, Cvin GPM