Water Control Valves - Flow Factor K_v Diagram

Sizing of water control valves - SI units

Example - a Water Valve and K_v value

The maximum pressure drop through a modulating control valve in a water flow system is designed to be 100 kPa. The flow through the valve is 5 liter/s. The required k_vvalue for the valve can be estimated as indicated in the diagram below to approximately 20.

Water Flow Control Valves Kv diagram chart example

Note - larger valves (with larger K_v) reduces the maximum pressure modulating spans - limiting the ability to provide a stable process control. As a consequence - control valves are often one to two dimensions below the dimensions of the connecting pipes.

Example - with a water flow of 5 liter/s the pipe size would be in the range 3 - 4 inches (80 - 100 mm nominal). A control valve would be in the size k_v ~ 20 - or in the range 2 - 3 inches (50 - 80 mm nominal).

Related Documents

Ball Valves - Flow Coefficients C_v - Flow coefficients - C_v - for typical ball valves - reduced and full bore.
Control Valves - Adding Flow Coefficients for Valves in Series or Parallel - How to add flow coefficients for control valves in series or parallel.
Flow Coefficient C_v vs. Flow Factor K_v - Comparing flow coefficients C_v to flow factors K_v.
Liquid, Steam and Gas - Flow Coefficients C_v - Calculate flow coefficients for the design of control valves - Imperial units.
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Water Control Valves - Flow Coefficient C_v Diagram - Sizing of water control valves - Imperial units.

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