## Flow Coefficient, Cv
## FLOW COEFFICIENT, FLOW RATE, PRESSURE DROP EQUATIONS
- Cv = Valve flow coefficient, dimensionless
- Q = Volumetric flow rate, gpm
- q = Volumetric flow rate, scfh
- Gf = Liquid specific gravity at upstream conditions [ratio of density of liquid at flowing temperature to density of water at 15.6°C (60°F)], dimensionless
- Gg = Gas specific gravity (ratio of flowing gas to density of air with both at standard conditions, which is equal to the ratio of the molecular weight of gas to the molecular weight of air), dimensionless
- DP = Pressure differential, psi
- T1 = Absolute upstream temperatures (in °R)
- P1 = Upstream absolute static pressure, psia
- P2 = Downstream absolute static pressure, psia
- Y = Expansion factor, ratio of flow coefficient for a gas to that for a liquid at the same Reynolds Number, dimensionless
(Y = 0.667 when P2 <= 0.5 times P1 for choked or critical flow, Y = 1.000 when P2 > 0.5 times P1 for very low pressure differential)
The above sizing equations are provided as courtesy and are derived from ISA-75.01 and ISA-75.02. |