The flow coefficient of a device is a relative measure of its efficiency at allowing fluid flow. It describes the relationship between the pressure drop across an orifice and the corresponding flow rate. A fluid is defined as a substance that continually deforms (flows) under an applied shear stress regardless of the magnitude of the applied stress. ... Pressure drop is a term used to describe the change in pressure across a system. ... In a typical mammalian body such as the human body, the body orifices are: the nostrils, for breathing and the associated sense of smell the mouth, for eating and vocalizations such as speech the ear canals, for the sense of hearing the anus, for defecation the urethra, for urination (and... In fluid dynamics, the volumetric flow rate, also volume flow rate and rate of fluid flow, is the volume of fluid which passes through a given volume per unit time (for example gallons per minute or squeaks per parsec). ...

Coefficent of discharge is ratio between the actual flow rate to Theoretical discharge.

In mathematical terms, the flow coefficient C_v is the volume (in gallons) of water at 60° F that will flow per minute through a valve with a pressure drop of 1 psi across the valve.

Numerically this definition can be expressed as:

The use of the flow coefficient offers a standard method of comparing valve capacities and sizing valves for specific applications that is widely accepted by industry. The general definition of the flow coefficient can be expanded into equations modeling the flow of liquids, gases and steam as follows:

Definitions

C_v = Flow coefficient or flow capacity rating of valve

F = Rate of flow in USGPM for liquids, SCFH for gases, and lbs/hr for steam.

delta P = Pressure drop across the valve, PSI