What is C v ?
If you are a mechanic, you would probably say that it is the joints that are on a front wheel drive vehicle, however if you work in the field of process automation you might know that it pertains to control valves.
C v is the capacity of a control valve, or the gallons of water that will pass through an orifice with a pressure drop of 1 psi in one minute at 60 degrees Fahrenheit. This is the basic formula for liquid flow with no pipe reducers:
Where:
- Q = Flow (gpm)
- Gf = flowing Specific gravity DP = Inlet pressure - outlet pressure in psia
- DP = P1 - P2
C v allows us to compare valves of completely different geometries. A partially open 3” ball valve could have the same C v as a fully open 2” ball valve and as a 4” globe valve. Don’t want to do the math? Many vendors have valve sizing programs available and there are also calculators on-line. In any case you still need to know what numbers to use for specific gravity and so forth and also note that C v or the capacity is not the only consideration when choosing a control valve.
