How this calculator works
Cv describes the US gallons per minute of water passing a valve at a one psi pressure drop under its reference conditions. Correct another liquid using its specific gravity relative to water. Enter an actual measured value for your liquid: product names alone do not fix density. The simple relation excludes cavitation, flashing, choking, viscosity correction and gas compressibility. Both endpoint pressures must use the same gauge or absolute reference.
Formula
Q_USgpm = Cv sqrt(delta p_psi/SG); Cv = Q_USgpm sqrt(SG/delta p_psi). SI conversion: 1 US gal/min = 0.0000630901964 m3/s and 1 psi = 6894.757293168 Pa.
Worked example
A Cv of 10 with water (SG = 1) and a one psi drop passes 10 US gal/min, or 0.000630901964 m3/s. A four psi drop passes 20 US gal/min.
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Frequently asked questions
Is Cv the same as Kv?
No. Kv uses m3/h and bar. Use the differential-pressure calculator when your flow factor follows that convention.
Can I use this for steam or air?
No. Compressible-flow sizing requires additional pressure, temperature and choking relations.
Can inlet pressure be gauge pressure?
Yes, if outlet pressure uses the same reference and you only need the difference. Cavitation checks require absolute pressures and are outside this model.