Control Valve Authority Calculator
Valve authority is the share of the total circuit pressure drop taken by the control valve. Low authority distorts the installed characteristic and makes control sluggish at low flow.
- N = ΔPvalve ÷ (ΔPvalve + ΔPsystem) = 0.5 ÷ 1.5 = 0.333
Valve Authority
Both pressure drops are taken at design flow with the valve fully open. A value of 0.25 to 0.5 is usually recommended.
Worked example
A valve dropping 0.5 bar in a circuit where piping and equipment drop 1.0 bar has N = 0.5 ÷ 1.5 = 0.33, a good value.
Frequently Asked Questions
What is a good valve authority?
Generally 0.25 to 0.5. Below 0.25 control becomes poor; above about 0.5 pumping energy is wasted.
Why does authority matter?
Because the system pressure drop changes with flow, the valve sees more pressure when nearly closed, which distorts its characteristic.
Is authority used in process plants?
The same idea is used as the ratio of valve drop to total system drop when choosing characteristics and sizing valves.
Learn more on the blog
Control valve flow coefficient (Cv) explained
A practical, field focused guide on instrumentationblog.in that explains the theory behind this calculator and how engineers apply it on real plants.
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