Engineering calculator reviewed for preliminary design use · Last updated: March 2026
Calculate control valve Cv using ISA/IEC standard methods. Determine Cv from liquid or gas flow rate, differential pressure, and fluid density for valve sizing. Apply to process control valve design and replacement.
Control Valve Cv Flow Coefficient
The Cv (valve flow coefficient) quantifies a valve's flow capacity. It is defined as the flow rate in US gallons per minute of water at 60°F that produces a 1 psi pressure drop. Cv is the fundamental parameter for control valve sizing.
Liquid Flow Formula (ISA-75)
Cv = Q × √(SG / ΔP)
Q: Volumetric flow rate [m³/h or USgpm]
SG: Specific gravity (water = 1.0)
ΔP: Pressure drop across valve [bar or psi]
Kv vs Cv
Kv (m³/h) is used in metric systems: Cv = 1.156 × Kv
Sizing Guidelines
Calculate Cv at maximum process flow, then select a valve with 1.3–1.5× margin. Oversized valves cause poor control performance.
Cv (flow coefficient) represents the flow capacity of a valve. Cv = 1 means the valve passes 1 US gallon per minute of water at 1 psi differential pressure. It is the primary sizing parameter for control valve selection.
Should I select a valve with Cv exactly matching the calculated value?
No. Select a valve where the calculated Cv falls between 60-80% of the valve's rated Cv at full open. This ensures adequate rangeability and avoids operating at extreme positions.
These results are preliminary estimates for screening-level design use. They do not replace detailed engineering, code compliance verification, or vendor-certified calculations.