The capacity factor of a valve, also called the valve coefficient; specifically, the number of gallons of water per minute that will flow through a valve with a pressure drop of 1 psi.

[Unless otherwise stated, CV factors are always stated for water flow. If the flow of 1 GPM of water through an orifice creates a 1 PSI pressure drop, the orifice has a rating of 1.0 C V. If 2 GPM can flow at a pressure drop of 1 PSI, the orifice has a rating of 2.0 CV, etc.
CV factors based on water flow must be corrected for viscosity and specific gravity of fluids other than water. Information on this page shows how to correct water-based CV factors for use on hydraulic fluids.]

See: “Cv Factors LVF Valves”