Flow Coefficient (Cv)

The flow coefficient (Cv) is a measurement of the amount of water that flows through a valve when fully open, divided by the corresponding ΔP across the valve. In simpler terms, it is a measure of how readily water will flow through a valve when given a pressure difference.

A higher Cv indicates greater water flow at any given pressure drop. The Cv can be thought of as a valve’s “size”, although it is not an actual physical measurement. Rather, the Cv is derived from the mathematical relationship between the flowrate of water and the ΔP across the valve.

This relationship is defined by what is known as the Bernoulli equation. To calculate the Cv of a particular valve, one must first determine the flowrate of water through the valve at a given ΔP. This can be done experimentally, or by using data from the manufacturer. Once the flowrate is known, the Cv can be calculated using the following equation: Cv = Q / (ΔP * 0.5885) where Q is the flowrate in gallons per minute (gpm), and ΔP is measured in pounds per square inch (psi).