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.