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It is well known that for the completely turbulent flow relationship between fluid flow
rate and pressure drop follows the power low. Flow coefficient is the proportional constant
between pressure drop and flow rate and it is determined experimentally by valve manufactures.
It is expressed as the flow rate of water in gpm u.s. (m3/h) for a pressure drop of 1 psi (1 bar)
across a flow passage.
Note: (flow coefficient: Cv-imperial, Kv-metric)
For correct control valve sizing it is important to calculate flow coefficient using this
calculator. When flow coefficient is calculated for required flow rate and known pressure drop,
selection of proper control valve can be done by selecting control valve with first bigger
flow coefficient.
Also using this calculator you can calculate maximum flow rate through control valve for given
pressure drop and known flow coefficient or valve size.
This version of calculator can be used for turbulent flow of water or other incompressible fluid, as viscosity
and expansion effect is not included. It means that for steam and gas control valve you will need
to use other calculation methods. Also, possible flashing and cavitation may reduce the control valve
capacity, as it is not treated in this version calculator.
Theory used for control valve sizing calculation
Flow coefficient, control valve sizing
Flashing and cavitation
Chocked flow
Flow mean velocity
note: calculator requires Java.
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