Valve Flow Coefficient

--
Cv (GPM/√psi)
Liquid Flow Formula

For liquids (Imperial units):

Cv = Q × √SG / √ΔP

Where:

  • Q = Flow rate (GPM)
  • SG = Specific gravity (water = 1.0)
  • ΔP = Pressure drop (psi)

For liquids (Metric units):

Cv = Q × √SG / √ΔP × 1.156

Where:

  • Q = Flow rate (m³/h)
  • SG = Specific gravity (water = 1.0)
  • ΔP = Pressure drop (bar)
  • 1.156 = Conversion factor
psi
How to Use This Tool
  1. Select whether your fluid is a liquid or gas
  2. Choose your preferred unit system (Imperial or Metric)
  3. Enter the required parameters:
    • For liquids: Flow rate, pressure drop, and specific gravity
    • For gases: Flow rate, upstream pressure, pressure drop, temperature, and compressibility factor
  4. The Cv value will be calculated automatically
  5. Use the Flow Curve tab to visualize how Cv changes with flow rate at a constant pressure drop
Understanding Cv

The Valve Flow Coefficient (Cv) is defined as the number of US gallons per minute of water that will flow through a valve with a pressure drop of 1 psi at 60°F. It's a crucial parameter for valve sizing and selection.

Engineering Notes
  • For liquids, Cv increases with higher flow rates and decreases with higher pressure drops
  • For gases, the relationship is more complex due to compressibility effects
  • Always consider the full range of operating conditions when selecting a valve
  • For critical applications, consult valve manufacturers' data and engineering standards
Typical Cv Ranges by Valve Type
Valve Type Typical Cv Range
Globe Valve 5 – 150
Ball Valve 10 – 300
Butterfly Valve 15 – 800
Needle Valve 0.1 – 10
Common Fluid Properties
Fluid Specific Gravity (Liquid) Compressibility Factor (Gas)
Water 1.0 N/A
Air N/A ~1.0 at low pressure
Oil (light) 0.85 N/A
Steam (saturated) N/A 0.8-0.9