Flow Formulas
General Information About Valve Sizing:
Valves with a "Full Port" have an internal seat diameter that is the same as the nominal pipe size, i.e. a 1 inch pipe size valve with a full port has a 1 inch diameter seat. Valves with a "Reduced Port" have an internal seat diameter that is smaller than the nominal pipe size.
The valve's flow coefficient, Cv, is a value that is determined by flow testing for each valve size. Full port valves will have a higher Cv than reduced port valves. The Cv rating for each valve is listed in the tables found in the valve catalog.
The definition of Cv is the # of gallons of water that will flow through the valve with a 1 PSI pressure differential when the valve is open.
The equations below can be used to determine:
- Flow Rate, given the Cv and ΔP
- Cv, given the Flow Rate and ΔP
- ΔP, given the Flow Rate and Cv
Symbols
- Cv = Valve's flow coefficient (dimensionless value)
- S = Specific Gravity (1.0 for air or water)
- T = Absolute Temperature in °R (°R = °F + 460)
- P1 = Inlet Pressure in PSIG
- ΔP = Pressure Differential in PSI across value in the open position
- V = Specific Volume in Cubic Feet per Pound
