Control valve Flow Characteristics (Inherent).

Control valve characteristics refer to the volumetric flow rate through the valve AND the valve travel from a close position to various degrees of opening state.

  1. Equal Percentage Opening
  2. Linear Opening
  3. Quick Opening.

1. Equal Percentage Opening:

Flow capacity increases rapidly as with the valve trim travel. The equal percentage increase of valve travel produces equal percentage changes in the existing valve coefficient (Cv).

  • This category of the valve is used in the processes where the large change in pressure drop are expected.
  • Used in the processes where a small percentage of the total pressure drop is allowed by the valve.
  • Used in Temperature and Pressure control loops.

 

2. Linear Opening:

Flow capacity increases with valve travel.

  • Used in the systems where the pressure drop across the valve is expected to remain fairly constant  ( i.e. steady-state systems)
  • Used in liquid level and flow loops.

 3. Quick Opening:

Produce large changes in the flow with small changes in the valve lift. It is limited to on/off service.