The valve coefficient, Cv, is a number which represents the capability of a valve (or any flow component) to flow a fluid. The larger the Cv, the larger the flow at a given pressure differential. By definition, a Cv value of one is the Cv required to flow one gallon per minute (gpm) of water at 60’ F with a pressure differential of one psi. Flow is proportional to the value of Cv.
For example, a Cv of 150 would then equate to 150 gpm of water at 60’ F with a differential pressure of one psi. The formula below allows for calculation of flow rate and pressure drop through a valve with a specified Cv value.
During the process of valve size selection, the same formula is used determine the valve Cv necessary for a required flow rate and desired pressure drop. Butterfly valve Cv values vary with the disc angle and valve size. In the chart below, we show the approximate Cv value of butterfly valves ranging from 2" to 24" and at various disc angles.
