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:

Where:

• 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