The flow factor Kv for control valves in water systems can be estimated from the diagram below:
- 1 bar = 1x105 Pa (N/m2)
Example - a Water Valve and Kv 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 kv value for the valve can be estimated as indicated in the diagram below to approximately 20.
Note - larger valves (with larger Kv) 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 kv ~ 20 - or in the range 2 - 3 inches (50 - 80 mm nominal).
Control Valve terminology, bodies, trim, flow characteristics, Cv and Kv sizing, noise, actuators and positioners
The study of fluids - liquids and gases. Involving velocity, pressure, density and temperature as functions of space and time.
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Comparing flow coefficients Cv to flow factors Kv.
Calculate flow coefficients for the design of control valves - Imperial units.
Calculate flow factor Kv for liquids, steam and gases - metric units.
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Sizing of water control valves - Imperial units.
Designing water process control valves and their Kv values.