How to find the necessary cV value for a valve for liquids:
Q = flow rate in gpm (US gallons)
G = specific gravity of liquid
DP = pressure drop = (inlet pressure – outlet pressure) (in psi)
| |
Q |
| CV = |
------------- |
| |
(DP /G)½ |
or..
Approximate specific gravities of some common liquids are:
| Acetone = 0.78 |
Benzene = 0.88 |
| Ethanol = 0.79 |
Kerosene = 0.80 |
| Water (fresh) = 1.00 |
Water (salt) = 1.03 |
Example:
A Series 18 Swagelok® valve has a CV of 1.8 when fully open. (at 2 turns open, it would be cV = 0.75)
For a flow of 6 gpm of benzene, the pressure drop will be approximately:
0.88 x (6/1.8)2 = 0.88 x 3.332= 9.8 psi
You may want to simply use our maximum flow or minimum CV calculator
Note: this relationship is widely published and commonly used in industry. It provides reasonable estimates for liquids with viscosities similar to water.
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