Equal Percentage Valves

Equal Percentage valves have a valve plug shaped so that each increment in valve percent open (lift) increases the flowrate by a certain percentage of the previous flow.

The relationship between valve lift and orifice size is not linear but logarithmic.

It is expressed mathematically as follows:



  • τ      = valve rangeability (ratio of the maximum to minimum controllable flowrate)

  • H       = valve  percent open or lift (0 = closed; 1= fully open)

  • Cv,max       = full open valve loss value