Valve Cv Calculator

Calculate the valve flow coefficient (Cv) for sizing control valves, determine flow rate from a known Cv value, or find the pressure drop across a valve. Supports both liquid and gas/steam applications.

Enter values to calculate

Valve Cv result

How It Works

The Valve Cv Calculator determines the flow coefficient (Cv) of a valve, which represents the volume of water in US gallons per minute (GPM) that will flow through a valve with a pressure drop of 1 psi at 60°F. Cv is the primary sizing parameter used by engineers to select the correct valve for a given application.

Liquid Cv Formula

For incompressible liquids, the valve Cv is calculated using:

Cv = Q × √(SG / ΔP)

Where:

  • • Cv = Valve flow coefficient
  • • Q = Volumetric flow rate (GPM)
  • • SG = Specific gravity relative to water at 60°F
  • • ΔP = Pressure drop across the valve (P1 - P2) in psi

Gas Cv Formula

For compressible gases and steam, the valve Cv is calculated using:

Cv = Q / (963 × √(ΔP × (P1 + P2) / (SG × T)))

Where:

  • • Q = Gas flow rate (SCFH - Standard Cubic Feet per Hour)
  • • ΔP = Pressure drop across the valve (psi)
  • • P1 = Inlet pressure (psia)
  • • P2 = Outlet pressure (psia)
  • • SG = Specific gravity relative to air
  • • T = Absolute temperature (Rankine = °F + 460)

Common Valve Cv Values

Typical Cv values for fully open valves by type and size:

Valve Type & Size Cv Range
1/2" Globe Valve 4 - 6
1" Globe Valve 10 - 15
2" Globe Valve 40 - 50
1" Ball Valve 30 - 40
2" Ball Valve 100 - 125
1" Butterfly Valve 35 - 45
2" Butterfly Valve 100 - 120
1" Gate Valve 20 - 30

FAQ

Here you will find the answers to the frequently asked questions about valve Cv and valve sizing.

Frequently Asked Questions

What is valve Cv and why is it important?

Valve Cv (flow coefficient) is a dimensionless number that represents the flow capacity of a valve. It is defined as the number of US gallons per minute of water at 60°F that will flow through a fully open valve with a pressure drop of 1 psi. Cv is the primary parameter used to size valves for a specific application, ensuring the valve can pass the required flow at the available pressure drop.

How do I size a control valve using Cv?

To size a control valve, first calculate the required Cv using the flow rate and available pressure drop. Then select a valve with a rated Cv that is 20-30% larger than the calculated Cv to allow for normal operating variations. The valve should operate between 10% and 80% of its travel range for optimal controllability. Always verify that the selected valve can handle the system's minimum and maximum flow requirements.

What ISA standards apply to valve sizing?

The primary standards for control valve sizing are ISA-75.01 (IEC 60534-2-1) for incompressible fluids and ISA-75.01 (IEC 60534-2-3) for compressible fluids. These standards define standardized methods for calculating Cv, accounting for factors such as critical pressure ratio, liquid vapor pressure, pipe geometry, and choked flow conditions. Following these standards ensures consistent and accurate valve selection across the industry.

What is critical flow and how does it affect valve sizing?

Critical flow (also called choked flow) occurs when the flow rate through a valve reaches a maximum and cannot increase further regardless of increasing pressure drop. For liquids, this happens when the pressure at the vena contracta drops below the fluid's vapor pressure, causing flashing or cavitation. For gases, critical flow occurs when the velocity reaches the speed of sound. In critical flow conditions, the standard Cv equations must be modified to account for the flow limitation.

What is the difference between Cv and Kv?

Cv and Kv are both valve flow coefficients but use different unit systems. Cv uses US gallons per minute and psi (imperial), while Kv uses cubic meters per hour and bar (metric). The conversion between them is Kv = 0.865 × Cv, or equivalently Cv = 1.156 × Kv. North American manufacturers typically use Cv, while European manufacturers often use Kv. Both values represent the same physical property of the valve's flow capacity.

Related Calculators

Continue your analysis with these related engineering tools

Head Loss Calculator

K-value method for fittings and valve head loss

Pressure Drop Calculator

Darcy-Weisbach pressure loss in piping systems

Flow Rate Calculator

Calculate pipe flow using the Hazen-Williams equation

Flow Rate Calculator

Professional hydraulic engineering calculators for engineers, technicians, and students.

Company & Resources

© 2026 Flow Rate Calculator. All rights reserved.

Privacy Policy Terms of Service Cookie Policy