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Valve Flow Coefficient
 

Below are some definitions and conversion factors for the three valve flow coefficients Kv, Cv and Qn.

What is the Kv Value?

Kv value is the metric measure for the flow of a valve. It is defined as:

The volume flow in cubic metres per hour of water at a temperature of between 5° and 40° celsius with a pressure drop across the valve of 1 bar.


What is the Cv Value?

Cv is the imperial measure for the flow of a valve. It is defined as:

The volume flow in US gallons per minute of water at a temperature of 60° fahrenheit with a pressure drop across the valve of 1 psi.


What is the Qn Value?

Qn value is used in pneumatics to define the flow of a valve. It is defined as:

The volume flow in litres per minute of air at a temperature of 20° celsius, with an input pressure of 6 bar and a pressure drop across the valve of 1 bar.


Converting between Kv, Cv & Qn

Kv = 0.86 x Cv
Kv = Qn / 1078

Cv = Kv / 0.86
Cv = Qn x 0.0008

Qn = Kv x 1078
Qn = Cv / 0.0008