For liquids the flow coefficient - Cv - is the flow capacity of a control valve and is in general determined experimentally and expressed in imperial units - GPM of water that a valve will pass for a pressure drop of 1 psi<pre>
Cv = q (SG / dp)1/2
where
q = water flow (US gallons per minute)
SG = Specific gravity (1 for water)
dp = pressure drop (psi)
The term “flow factor” - Kv - is in common use as well, but express the capacity in SI-units.
Kv = 11.7 q (SG / dp)1/2
where
q = water flow (m3/h)
SG = Specific gravity(1 for water)
dp = pressure drop (kPa)
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[Please note that the 1/2 behind the bracket is suppose to be to the exponent 1/2 and not bracket times 1/2] Can't seem to get it right in this text.
Once you have calculated the cv of the valve that is required you can go to any manufacturer and select the correct size valve for your application but keep in mind this calculation is for a liquid valve application only.