Control valves refer to valve devices that control conditions such as fluid flow and temperature by fully or partially closing or opening. This valve moment is based on signals provided by a sensor received by controllers, which compare the current sensor value to a process value. These values are calculated via the control valve (Cv) or flow coefficient.
The flow coefficient refers to the measure of a device’s efficiency in enabling the flow of a fluid. Flow coefficients essentially determine how the flow rate corresponds to the rate of pressure drop in the control valve.
Elements used in the calculation of the flow coefficient include the specific gravity of water, which is divided by the pressure drop across the control valve in pounds per square inch (psi). The square root of this value is calculated into F, the rate of flow in gallons per minute, to determine the Cv, or flow coefficient.
The control valve Cv provides a method of comparing valve sizes and capacities for various industry applications. The flow coefficient equation can also be used as the basis for other equations pertaining to fluid or gas flow, such as the coefficient of discharge, or ratio of real flow rate to the theoretical rate of discharge.
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