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Flow Valve (Cv/Kv) Sizing Calculator

Determine flow coefficient for control valves based on flow rate and pressure.

Process Conditions (Liquid)

GPM
psi

Water at 60°F (15°C) = 1.0

Valve Flow Coefficient

31.62 Cv
Equivalent Kv: 27.35
info
Disclaimer of Liability: This calculator is provided for educational and estimation purposes only. By using this tool, you agree to discharge AutomationView of any liability for direct, indirect, or consequential damages resulting from its use. It is your strict responsibility to independently verify all calculations, validate the results against official manufacturer documentation, and ensure compliance with all applicable safety and engineering standards before implementing any parameters in a production environment.

What is Valve Flow Sizing?

Properly sizing a control valve is critical in industrial fluid processing. If a valve is too small, it restricts flow and causes excessive pressure drops. If it is too large, it operates near its closed position, leading to poor control resolution, wear, and cavitation. Sizing is determined using the flow coefficient: Cv (Imperial) or Kv (Metric).

Understanding Cv and Kv

  • Cv (Flow Coefficient): The volume of water (in US GPM) at 60°F that will flow through a valve with a pressure drop of 1 psi.
  • Kv (Flow Factor): The volume of water (in m³/h) at 20°C that will flow through a valve with a pressure drop of 1 bar.

Standard Formulas for Liquids

Because liquids are incompressible, the sizing formulas are straightforward and rely on the required flow rate ($Q$), the Specific Gravity ($SG$) of the fluid, and the allowed pressure drop ($Delta P$).

Imperial Sizing (Cv):

$Cv = Q times sqrt{SG / Delta P}$

Where $Q$ is in US GPM, $SG$ is specific gravity (Water = 1.0), and $Delta P$ is the pressure drop in psi.

Metric Sizing (Kv):

$Kv = Q times sqrt{SG / Delta P}$

Where $Q$ is in m³/h, and $Delta P$ is the pressure drop in bar.

Converting Between Cv and Kv

To cross-reference datasheets from European and American manufacturers, you can convert between the coefficients using these industry-standard multipliers:

  • $Kv approx 0.865 times Cv$
  • $Cv approx 1.156 times Kv$

Considerations for Compressible Fluids

Sizing valves for gases and steam requires significantly more complex calculations. Because gas density changes with pressure, equations must factor in absolute inlet pressure, absolute temperature, and distinguish between sub-critical flow and choked (critical) flow conditions.