Cv Flow Calculator

About valve flow coefficient

Cv is a standardized measure of a valve's liquid-flow capacity. One Cv represents the capacity to pass one US gallon of water per minute with a pressure drop of one psi under the reference conditions used by the customary equation. For liquids without a viscosity correction, Cv = Q × √(SG/ΔP), where Q is flow in US gallons per minute, SG is specific gravity relative to water, and ΔP is pressure drop in psi. This calculator obtains specific gravity by dividing the entered density in pounds per cubic foot by 62.4. A larger Cv means that a valve can pass more liquid at a given pressure drop. Doubling flow while holding pressure drop and density constant doubles the required Cv. Increasing pressure drop by a factor of four halves the required Cv, while a denser liquid needs a higher Cv than water at the same flow and drop. Valve manufacturers publish rated Cv values by opening position, so the calculated requirement can be compared with an appropriate operating point rather than merely the fully open rating. The additional pipe inputs provide useful context. Flow rate and inside diameter determine average pipe velocity after gallons per minute are converted to cubic feet per second. Density, velocity, diameter, and dynamic viscosity determine Reynolds number. Values below about 2,300 are labeled laminar, values from 2,300 to below 4,000 transitional, and larger values turbulent. Temperature is recorded because density and viscosity should correspond to the same operating temperature, although it does not independently alter the Cv equation once those fluid properties are supplied. This calculation is intended for single-phase, incompressible liquid flow. Gas, steam, flashing, cavitating, or choked service requires different sizing equations and additional thermodynamic data. Very viscous liquids can also require a Reynolds-number correction to the preliminary Cv. Fittings, reducers, and nonstandard installation geometry may change the effective pressure loss and the valve correction factors required by recognized sizing standards. Use actual operating flow, valve pressure drop rather than total system pressure, and fluid properties at operating temperature. Pipe diameter means inside diameter, not nominal size. The result is an engineering estimate for screening and comparison; final valve selection should follow the manufacturer's sizing procedure, rangeability limits, noise and cavitation checks, material compatibility, and applicable process-safety requirements.

Cv flow examples

These liquid cases apply the standard non-viscous Cv relationship.

How to calculate Cv

1. Enter the required liquid flow in US gallons per minute.
2. Enter the pressure drop assigned to the valve in psi.
3. Supply density, temperature, and dynamic viscosity for the operating fluid.
4. Enter the pipe inside diameter in inches.
5. Select Calculate and compare the required Cv with manufacturer data.

Frequently asked questions