Flow coefficient

Article summary

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 valve or other assembly and the corresponding flow rate. A greater restriction in flow will create a larger pressure drop across a device and thus a smaller flow coefficient, conversely device with little restriction in flow will have a small pressure drop and a larger flow coefficient. For example, the flow coefficient of a 1" ball valve may be 80 while a similarly sized globe valve in the same application may be 10. Mathematically the flow coefficient (or flow-capacity rating of valve) can be expressed as C_\text{v} = Q \sqrt{\frac{\text{RD}}{\Delta P}}, where, : is the rate of flow (expressed in US gallons per minute), : RD is the relative density of the fluid (for water = 1), : is the pressure drop across the valve (expressed in psi). In more practical terms, the flow coefficient is the volume (in US gallons) of water at that will flow per minute through a valve with a pressure drop of across the valve. 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.…

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