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.
- Equal Percentage Opening
- Linear Opening
- 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.