What is the difference between linear characteristics and equal percentage valve?



Linear Characteristics

The linear characteristics valve plug is shaped so that the flow rate is directly proportional to the valve lift,at a constant differential pressure.A linear valve achieve this by having a linear relationship between the valve lift and the orifice pass area.

For example at 50% valve lift a 50% orifice size allows 50% of the full flow to pass.

Equal Percentage Characteristics

These valves have a valve plug shaped so that each increment in valve lift increases the flow rate by a certain percentage of the previous flow. The relationship between valve lift and orifice size is not linear but logarithmic.

Table below shows how the change in flow rate alters across the range of valve lift for the equal percentage valve with a rangeability of 50 and with a constant differential pressure.