how electro pneumatic positioner works ?

By | June 2, 2016

  The electro -pneumatic positioner is used in Control Valves with pneumatically operated actuators. The valve is operated by means of electrical controller or Control Systems With an control signal of 4 to 20 mA or split ranges of 4~12/ 12~20 mA.

Electro-Pneumatic Positioner converts this control signal into a pneumatic
output in proportion to the lift of the control valve.


1. There is no change in performance in the range of 5-200Hz of Vibrations.
2. Can be Used for Split Range Application
3. Easy to adjust zero and span & calibrate to the required travel of the valve.
4. Easy to convert from ATO (Air to Open) to ATC (Air to Close) action or vice versa.
5. Easy Feedback connection.
6. Fast and accurate response.
7. Low air consumption


This equipment works on the force balance principle and uses a flapper/ nozzle & set of springs to bring the forces under equilibrium at the required valve position with respect to the signal/command given to it.
When the input signal from the controller is applied to the torque motor, the armature receives torque in counter clock wise direction, due to this torque the counter weight/ flapper moves towards left side and the clearance between the Nozzle & the Flapper increases, due to which, the back pressure in the Nozzle decreases.


As a result of the above, the exhaust valve of the Pilot Valve moves towards right and the Inlet Valve “A” opens, thereby the supply air goes to the actuator through port OUT1. The valve Spindle will move up or down depending up on the actuator configuration (ATO/ATC) and the Feedback Spring will lengthen or shortens by the movement of Feedback Lever.
When there is a force balance between Feedback Spring tension and the Torque generated by the Torque Motor, the valve Spindle stays in it’s position.


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