Flow Coefficient

Written by Jerry Ratzlaff. 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.

formula

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

Where:

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