Control loops are added to a process to control the process. In control loops, flow control loops are laster loops among them.
A valve is used in a control system to control the flow of the fluid inside the pipe system. So valves are the control element in flow control system.
The flow inside the pipeline is measured using flow measurement devices such as an orifice, venturi, ultrasonic flow measuring devices. The measured value is transmitted using the flow transmitter to the controller.
The controller compares the measured value with the setpoint value. The setpoint is the preset value which is the required flow value. The difference in the value is given to the control device, which is valve here to take a proper control action.
If the measured value is greater than the setpoint then the value is controlled to close and block the flow so that flows set to required flow.
If the measured value is less than the setpoint, then the valve open further to maintain the required flow.
Every control loop uses the pneumatic and electric signals.
The flow transmitter sends 4-20mA signal which indicates the flow parameter and acceptable to the controller. The controller sends the control action through pneumatic signal within 3-15 psi pressure standard. Valve actuators move according to the pneumatic signal send by the controller.