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.