“The most common final control element in the process control industries is the control valve. The control valve manipulates a flowing fluid, such as gas, steam, water, or chemical compounds, to compensate for the load disturbance and keep the regulated process variable as close as possible to the desired set point.”
Process plants consist of hundreds, or even thousands, of control loops all networked together to produce an end product/ products. Each of these control loops is designed to keep some important process variable such as pressure, flow, level, temperature, etc. within a required operating range to ensure the quality of the end product. Each of these loops receives and internally creates disturbances that detrimentally affect the process variable, and interaction from other loops in the network provides disturbances that influence the process variable.
To reduce the effect of these load disturbances, sensors and transmitters collect information about the process variable and its relationship to some desired set point. A controller then processes this information and decides what must be done to get the process variable back to where it should be after a load disturbance occurs. When all the measuring, comparing, and calculating are done, some type of final control element must implement the strategy selected by the controller. These final control elements may be various types based on their applications such as control valves, solenoid valves, motors etc. Control Valves are most suitable for regulation of the rate of fluid flow as the position of the valve plug or disk is changed by force from the actuator.
We will discuss control valve on the bases of following :-