K_v Diagram Water Valves

K_v diagram for modulating water valves

The diagram below can be used to estimate the k_v values for valves in water systems.

Example - Water Valve and K_v value

The maximum pressure drop through a modulating regulating valve in a water flow system is estimated to 100 kPa. The flow through the valve is 5 liter/s. The k_v value for the required valve can be estimated in the diagram below to approximately 20.

Note - a larger valve (with larger k_v) will reduce the maximum pressure modulating span - limiting the ability to provide stable regulating of the process. As a consequence it is normal that regulating valves are one or two dimensions below dimensions of connecting pipes.

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

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