Does a ball valve require a Cv value?
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Ball valve, ON/OFF, is a Cv value required?
The flow coefficient Cv value is an important parameter for control valves; it reflects the capacity of the valve. The nominal diameter of the control valve is determined based on the value of Cv. The Cv value is defined as the number of US gallons per minute of clean water at 60°F (15.6°C) that pass through the valve, under the condition that the valve is fully open and the pressure difference across it is 1 pound per square inch. China’s flow coefficient is defined according to the metric system. The symbol is Kv; the relationship between Kv and Cv is Cv=1.17Kv
The Cv value of a valve and its opening degree are two distinct concepts; abroad, it is commonly referred to as Cv, while in China it is usually called Kv. Kv represents the flow capacity of the valve, and it is defined as the volume of fluid that passes through the valve per hour, expressed in m3/h or t/h, when the control valve is fully open, the pressure difference ΔP across the valve is 100 KPa, and the density of the fluid is 1 gf/cm3 (i.e., normal water temperature). (For example, a control valve with Kv=50 means that when the pressure difference across the valve is 100 KPa, the water flow rate is 50 m3/h.) ）
The valve opening degree refers to the position of the valve core (or valve plate) when it moves in order to change the throttling area of the flow passage during regulation; it is generally expressed as a percentage, with 0% indicating a closed state and 100% indicating a fully open state. For butterfly valves, manufacturers sometimes provide a Cv–opening curve; in this case, Cv represents the flow capacity of the valve at different opening degrees.
Factors affecting Cv value: * Diameter at the pipe inlet: too small * Length of the pipe * Opening of the valve body * Laminar flow, turbulent flow * Too close to the ends of the tees * Shape of the valve body inlet
Just make sure the manufacturer doesn’t reduce the neck size; there’s no need to calculate Cv
There are also CV values, but they are generally ignored when making a choice; the pipe diameter is what matters.
That makes sense; a full-bore ball valve is not necessary
Most O-type ball valves are used as shut-off valves, so no calculation is required