In this Post, we will discuss the control valve Positioner.
Control valve positioner
Control valve positioner works as an actuator for a pneumatic control valve. As the name indicates, control valve positioner controls the position of a pneumatic control valve. A valve positioner is a device which accurately positions the control valve in accordance with the pneumatic control signal.
The control signal is routed to the positioner where comparison of the valve actual position to the desired control signal is used to develop an output pneumatic signal which operates the control valve. A globe valve can be used to respond in an equal or linear percentage manner.
The positioner compares the control signal (the desired valve position) with the actual valve position through a mechanical feedback linkage. If the control valve position is incorrect, the positioner will either load or exhaust air from the valve actuator until the correct valve position is obtained.
A pneumatic positioner requires both a control signal and an instrument air supply signal to operate.
Positioner comes equipped with three gauges,
- To indicate the air supply signal
- To indicate instrument signal (Normally comes from I/P converter).
- To indicate output signal (Given to the pneumatic control valve).
There are 3 pressure gauges in control valve positioner.
Instrument air comes from an i/p converter(0.2 to 1.0 kg/cm^2)
Valve air supplied to control valve.
Supply Air is an air supply for pneumatic positioner.
Parts of a pneumatic control valve positioner
the adjuster is used to adjusting the position of a control valve if the control valve is not fully closed or opened after giving signal it can be closed or opened by adjuster screw.
Cam is used to operate a pneumatic control valve.
Bypass Switch Assembly
Bypass Switch Assemble has 2 positions
In bypass position control valve operation is only closed or opened. % opening is not performed in the bypass position.
In Positioner mode position % (percentage) opening is performed.
Travel pin provides connection between positioner and control valve.
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