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Control Valve · Glossary

What is Valve Rangeability?

max ÷ min controllable CvControl Valve

Valve rangeability is the ratio of the largest to the smallest flow coefficient over which a valve still follows its characteristic.

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Valve Rangeability Explained

Inherent rangeability describes the trim. Installed rangeability, the useful ratio of flows in service, is usually much lower because pressure drop changes and the valve should not run very close to its seat.

Check rangeability when one valve must handle both start up and full load.

Valve Rangeability Formula

R = Cvmax ÷ Cvmin
CvmaxCv at maximum controllable opening
Cvminsmallest Cv still within the characteristic
Example: Cv 200 at full travel and 4 at minimum: R = 50.

Valve Rangeability: Typical Values

Globe valveabout 30:1 to 50:1
Segmented V balloften 100:1 or more
Butterflyabout 20:1
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Calculators for Valve Rangeability

CalculatorValve Rangeability CalculatorFree online calculator with formula and worked example.CalculatorSplit Range CalculatorFree online calculator with formula and worked example.

Free Downloads

Free downloadControl Valve Cheat SheetFree printable PDF cheat sheet.

Frequently Asked Questions

What is Valve Rangeability?

Valve rangeability is the ratio of the largest to the smallest flow coefficient over which a valve still follows its characteristic.

How do I cover a very wide range?

Use two valves in split range or parallel, one small and one large.

Is rangeability the same as turndown?

The ideas are similar; for valves, rangeability is the usual term.

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