Cv PDF E-mail
Cv, the flow coefficient, is the relative measure of a device's ability to flow water. In a constant, established water flow, the flow coefficient is determined by the volume of water flow through the valve and the inlet and outlet pressures. When holding the inlet and outlet pressures constant, the Cv of a given valve is also constant. Why do we use Cv?
Cv gives us a method to compare flow capabilities of different valves. The flow coefficient allows us to determine what size valve is required for a given application.
What affects Cv?
Several factors have an impact on the flow coefficient. Some of them are listed below:
  • Orifice size (diameter of the piping or opening through the valve)
  • Length of piping or opening through the valve
  • Turbulence caused by bends or turns in the piping
  • Restrictions, or anything that reduces the orifice size or the flow path
  • Shape of the orifice 

Types of Cv
When components of a  circuit are arranged in series with each other, water flow goes through all the components in the circuit, and there is one flow path. Conversely, when the components are connected in parallel, flow is divided among all the components in the circuit, and there is more than one flow path.   
  Things to remember when considering Cv
When comparing valves that have the same pipe size, line-mounted valves generally have a higher Cv than base-mounted valves. This difference results because line-mounted valves have straighter flow paths with fewer restrictions.

 
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