CvAvailable
Valve Cv Calculator
CalculatorCalculate liquid valve Cv from flow, valve pressure drop, and specific gravity.
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Valve Authority Calculator
See how much of the circuit pressure drop occurs across the control valve.
Quick start
Enter the fully open valve pressure drop and the remaining circuit loss at the same design flow. Exclude the control valve from the remaining loss. Select Calculate to see the authority and pressure-drop split.
Inputs
Use pressure drops at the same design flow, with the control valve fully open.
Result
Enable JavaScript to calculate.
Method & assumptions
a = ΔPv / (ΔPv + ΔPrest)
The calculator uses a fixed differential pressure across a selected series circuit. Both losses refer to the same design flow. Under this assumption, the fully closed valve sees the circuit differential pressure, while the fully open valve shares it with the other components.
Convert both inputs to kPa before adding them. If you know the total circuit loss, subtract the valve loss before entering the rest-of-circuit value.
Reference: Belimo · Electronic Valve Application Guide, printed pp. 11 and 14.
Worked example
A 10 kPa fully open valve loss plus 20 kPa of remaining circuit loss gives a total of 30 kPa. Authority = 10 / 30 = 0.3333, or 33.33%.
Frequently asked questions
Is authority the same as valve opening?
No. Authority is a pressure-drop ratio evaluated with the valve fully open. It is not the actuator position or valve command.
Does this result pass or fail?
The calculator does not assign a universal acceptance threshold. Review the valve characteristic, circuit design and project criteria together.
Why can authority be 1?
If the entered remaining loss is zero, all of this model's circuit pressure drop occurs at the valve. That limiting case does not establish real-world system performance.
Recommended parts
Product recommendations have not been added. This calculation does not select a valve model.
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