What Is Control Valve Cv?
Control valve Cv, or valve flow coefficient , measures a valve's flow capacity. One Cv equals 1 US gallon of water per minute at 60°F flowing through a valve with a pressure drop of 1 psi. Engineers calculate the required Cv to select a valve with enough capacity for the process.
In control valve sizing, the required Cv must be compared with the manufacturer's rated Cv at different valve travel positions. The largest available Cv is not automatically the best choice. An oversized valve may control too close to the seat, while an undersized valve may not deliver the required maximum flow.
Final selection should also check flow characteristic, rangeability, pressure recovery, cavitation or flashing risk, noise, materials, shut-off class and available actuator thrust. Cv is the starting point for sizing, not the complete valve specification.
Control Valve Cv Sizing by Fluid Type
-
Liquid Service
Calculate Cv from the design flow rate, available valve pressure drop and liquid specific gravity. Then check vapour pressure and pressure recovery to identify cavitation, flashing or choked flow.
-
Gas Service
Use absolute inlet and outlet pressure, operating temperature, gas specific gravity or molecular weight, compressibility factor and specific heat ratio. Check whether the flow becomes choked.
-
Steam Service
Use mass flow, absolute inlet and outlet pressure, and the steam condition—saturated or superheated. Confirm the critical pressure-drop limit and expected noise before choosing the valve size and trim.
Need Control Valve Sizing Support?
Send your medium, flow rate, inlet pressure, outlet pressure, temperature and connection standard. MacoTango Valve can help review Cv, valve type, actuator selection and project documentation.
Frequently Asked Questions About Valve Cv
Cv is the valve flow coefficient. It represents valve flow capacity and is used to compare valve sizes and select a suitable control valve for a required flow and pressure drop.
Yes. The calculator includes separate sizing inputs for liquid, gas and steam service conditions, helping engineers estimate Cv for common industrial process applications.
For gas and steam sizing, absolute pressure should be used. Using gauge pressure can lead to incorrect Cv results because compressible flow depends on absolute pressure conditions.
No. Cv is an important starting point, but final selection should also consider valve type, trim, material, pressure class, temperature, cavitation, noise and actuator requirements.
Prepare the fluid medium, normal and maximum flow, inlet pressure, outlet pressure, temperature, density, pipe size, connection standard, pressure class and any noise or cavitation limits.