Definition of Linear and Equal Percent Characteristics?

Equal Percent characteristics.

The change of flow resulting from a fixed increment of valve travel is directly proportional to the flow immediately before the change took place.

Linear characteristics.

The change in flow resulting from a fixed increment of valve travel is constant throughout the whole stroke.

General rules.

  1. Use Equal Percent if in doubt.
  2. Use Linear for level control.
  3. Use Equal Percent for pressure control.
  4. Use Linear when the pressure drop across the valve is a large proportion of the total pressure drop.