A pneumatic positioner is a device mounted on a control valve that ensures the valve stem position accurately corresponds to the control signal it receives. Its principle of operation involves a closed-loop feedback system that compares the desired valve position (as indicated by the control signal) with the actual valve position. The positioner then adjusts the pneumatic pressure applied to the valve actuator until the desired position is achieved. The main components of a pneumatic positioner include a beam or lever mechanically linked to the valve stem, a flapper-nozzle mechanism, a pilot val....
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