Process plants consist of hundreds, or even thousands, of control loops all networked together to produce a product to be offered for sale. 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.
The control valve is a critical part of the control loop. The control valve manipulates a flowing fluid, such as gas, steam, water, or chemical compounds to compensate for the load disturbance and keeps the regulated process variable as close as possible to the desired set point.
Control Valve Arrangement
The image below shows how a control valve can be used to control rate of flow in a line. The “controller” receives the pressure signals, compares them with pressure drop for the desired flow and if the actual flow is different, adjusts the control valve to increase or decrease the flow. Comparable arrangements can be devised to control any of numerous process variables. Temperature, pressure, level and flow rate are the most common controlled variables.