As the final control element in most process control and automation systems, control valves are part of a complex system-within-a-system in which the valve positioner can be an integral component.
The control valve is made up of four principal sub-systems:
- The valve body, which includes the bonnet and piping inlet and outlet connections.
- The valve trim, plug, stem, cages, retainers and disc, used to control the flow through the valve body.
- The actuator, used to provide power to move the valve stem or shaft.
- The positioner, used to control the position of the valve stem and provide linearization.