Flow Coefficient

Written by Jerry Ratzlaff on . Posted in Properties

Flow coefficient can be described as the volume (in US gallons) of water at 60°F that will flow per minute through a valve with a pressure drop of 1 psi across the valve. This gives us a method to compare flow capabilities of different valves. The flow coefficient allows us to determine what size valve is required for a given application.

Flow Coefficient is primarily used when sizing control valves. However, it can be used to characterize other types of valves such as ball valves and butterfly valves.


\(C_v = Q \sqrt {\frac{SG} {\Delta p} }\)


The general definition of the flow coefficient can be expanded into equations modeling the flow of liquids, gases and steam as follows:

\(C_v\) = flow coefficient

\(Q\) = flow rate capacity

\(SG\) = specific gravity of fluid (water at 60°F = 1.0000)

\(\Delta p\) = pressure differential