Flow coefficient (Cv for control valve) is the capability of a valve to flow a liquid. One Cv is equal to a flow of 1 gallon per minute (gpm) of water at 60 degrees Fahrenheit with a pressure differential of 1 pound per square inch. The larger the Cv, the greater the flow in gpm. If you are dealing with a pressure differential other than 1 pound per square inch (psi), then gpm can be calculated in a few steps.
Things You'll Need
 Calculator

Determine the pressure differential of the valve by subtracting the downstream pressure from the upstream pressure.

Take the square root of the pressure differential.

Multiply the square root of the pressure differential by the valve coefficient to calculate the flow in gallons per minute.
References
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