Control valve is a type of final control element that is most commonly used for process control systems. Control valve serves to regulate flow of fluid so it can be determined in accordance with controller's requirement. Valve has important role in steam boiler.
Most of control valve characteristics that are used in industrial process are as follow:
- Linear Characteristic
The control valve will give increment value of flow rate close to each increment travel (proportional).
- Equal percentage characteristic
The percentage of valve opening (valve travel) will give same percentage of amount of flow rate.
- Quick opening characteristic
Control valve provide maximum change in flow with small valve opening and maintain linear relationship at all positions of fluid movement. Each additional valve opening provides sharp change in flow rate and when the valve approaching full opening position, flow changes near zero.
A control valve consists of two parts, actuator and valve as shown in Figure 2.5 below:
|Figure 1: Control Valve|
Actuator part is the part that moves to perform on open / close valve. This part is widely used is pneumatic operated (diaphragm), electric actuators, hydraulic actuators, and manual / hand operated actuator. Spring and pneumatic diaphragm actuator are widely used because of the ability and its structure is simple.
Valve Parts are mechanical components that determine amount of flow that goes into process. In its unity as the unit control valve, actuator and valve must perform correction based on manipulated variable signal which coming out of controller.