Cv Flow Calculator
Calculate valve flow coefficient (Cv), flow rate, and pressure drop for hydraulic systems
Calculate Valve Flow Parameters
Fluid Properties
Density relative to water (water = 1.0)
Volume flow rate through the valve
Pressure upstream of the valve
Pressure downstream of the valve
Results
Formula used: Cv = Q × √(SG / ΔP)
Where: Q = Flow rate (GPM), SG = Specific gravity, ΔP = Pressure drop (PSI)
Definition: Cv is the flow of water (in GPM at 60°F) through a valve with 1 PSI pressure drop
Example Calculation
Water Flow Through Control Valve
Problem: Find the Cv for a valve passing 100 GPM of water
Flow rate: 100 GPM
Fluid: Water (SG = 1.0)
Inlet pressure: 50 PSI
Outlet pressure: 45 PSI
Pressure drop: 5 PSI
Solution
Cv = Q × √(SG / ΔP)
Cv = 100 × √(1.0 / 5)
Cv = 100 × √0.2
Cv = 100 × 0.447
Cv = 44.7
Common Valve Types & Cv Ranges
Ball Valve
Cv: 0.1 - 1000+
Full bore, quarter turn
Globe Valve
Cv: 0.1 - 500+
Good throttling control
Butterfly Valve
Cv: 10 - 5000+
Large diameter applications
Design Tips
Select Cv 10-20% higher than calculated for safety margin
Higher Cv means less pressure drop at given flow
Cv varies with valve opening percentage
Consider fluid viscosity for non-water fluids
Understanding Cv Flow Coefficient
What is Cv?
The valve flow coefficient (Cv) is a measure of the flow capacity of a valve. It is defined as the number of US gallons of water at 60°F that will flow through a valve per minute with a pressure drop of 1 psi across the valve.
Why is Cv Important?
- •Enables proper valve sizing for required flow rates
- •Helps predict pressure losses in piping systems
- •Essential for control valve selection and system design
- •Prevents oversizing (waste) or undersizing (poor performance)
Formula Explanation
Cv = Q × √(SG / ΔP)
- Cv: Flow coefficient (US gal/min at 1 psi drop)
- Q: Flow rate (US gallons per minute)
- SG: Specific gravity (relative to water)
- ΔP: Pressure drop across valve (psi)
Note: This formula applies to liquid flow. Gas flow requires different calculations considering compressibility effects.
Valve Selection Guidelines
Control Applications
Use globe or needle valves with precise Cv curves for accurate flow control
On/Off Service
Ball or gate valves with high Cv values for minimal pressure drop
Large Diameter
Butterfly valves offer high Cv in compact design for large pipes