Cv Flow
Calculate valve flow coefficient Cv = Q × √(SG/ΔP) for liquid valve sizing. Enter flow rate, specific gravity, and pressure drop for instant results with charts and breakdowns.
About This Calculator
The Cv Flow Calculator computes the valve flow coefficient (Cv) for liquid piping systems using the standard ISA formula Cv = Q × √(SG / ΔP). This essential engineering tool helps mechanical engineers, piping designers, and maintenance professionals select the correct valve size for any liquid flow application.
The valve flow coefficient (Cv) measures how much fluid can pass through a valve at a given pressure drop. Specifically, one Cv represents a flow of 1 US gallon per minute of water at 60°F with a 1 psi pressure drop. The calculator supports two modes: calculate the required Cv from a known flow rate and pressure conditions, or calculate the expected flow rate from a known Cv value. It includes preset specific gravity values for water, ethanol, methanol, acetone, gasoline, benzene, and sea water, along with a custom option for any fluid.
Formula
Cv = Q × √(SG / ΔP)
Where:
- Cv = Valve flow coefficient (GPM at 1 psi drop)
- Q = Flow rate (US gallons per minute)
- SG = Specific gravity of the fluid (dimensionless)
- ΔP = Pressure drop across the valve (psi) = P₁ − P₂
Regional Notes
United States & Global: Cv is the standard flow coefficient used throughout North America for valve sizing per ISA-75.01.01 / IEC 60534-2-1 standards. In Europe and Asia, the metric equivalent Kv (m³/h at 1 bar drop) is more common — convert using Kv = Cv / 1.156. The calculator uses imperial units (GPM, psi) as Cv is defined in US gallons.
Frequently Asked Questions
What is valve flow coefficient (Cv)?
The valve flow coefficient (Cv) is a measure of a valve's capacity to let fluid pass through. It is defined as the volume of water at 60°F in US gallons per minute that will flow through a valve with a pressure drop of 1 psi across it.
How do you calculate Cv for a valve?
Cv is calculated using the formula Cv = Q × √(SG / ΔP), where Q is the flow rate in GPM, SG is the specific gravity of the fluid, and ΔP is the pressure drop across the valve in psi.
What is the difference between Cv and Kv?
Cv is the imperial flow coefficient (US gallons per minute at 1 psi drop). Kv is the metric equivalent (m³/h at 1 bar drop). The conversion is Cv = 1.156 × Kv.
Is the Cv Flow calculator free to use?
Yes, the Cv Flow calculator is completely free to use with no registration required.
Can I calculate flow rate from a known Cv value?
Yes, the calculator supports both modes: calculate Cv from flow rate and pressure drop, or calculate flow rate from a known Cv value.
What fluids are supported by the Cv calculator?
The calculator includes presets for water, ethanol, methanol, acetone, gasoline, benzene, sea water, and a custom option for any fluid with a known specific gravity.
Why is Cv important for valve selection?
Cv helps engineers select the right valve size for an application. An undersized valve restricts flow, while an oversized valve causes poor control and energy waste.