Water Control Valves - Flow Factor Kv Diagram

The flow factor K_v for control valves in water systems can be estimated from the diagram below:

• 1 bar = 1×10⁵ Pa (N/m²)

• Download Kv diagram for water flow

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_v value for the valve can be estimated as indicated in the diagram below to approximately 20.

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).