How this calculator works
A fixed valve or calibrated restriction often has an approximately quadratic liquid pressure-flow relation. This tool defines its flow factor as Kv, so a value of one passes one cubic metre per hour of reference water at a one bar drop. Specific gravity corrects the pressure drop for another liquid. Use a measured density ratio rather than a generic product name. The coefficient convention matters: a US Cv entered as Kv gives an incorrect answer.
Formula
Delta p_bar = SG (Q_m3/h/Kv)^2. In SI: delta p_Pa = 100000 SG (3600 Q_m3/s/Kv)^2.
Worked example
At Q = 0.001 m3/s, Kv = 3.6 and SG = 1, the differential pressure is 100000 Pa. Doubling flow gives 400000 Pa.
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Frequently asked questions
What does the flow factor mean?
It is Kv under the metric water convention stated on this page. Check the units on the valve datasheet.
Does a zero pressure difference determine Kv?
No. Zero flow and zero pressure drop cannot identify a finite flow coefficient uniquely.
Can I apply the relation to a gas?
Use a compressible-flow model for gases, especially when the pressure ratio is large or choking is possible.