Answer / himanshu amin

valve positioner is having three air connection. 1. Air
supply,2. i/p 3 to 15 psi from i/p converter. 3. o/p to
control valve. suppose you are giving 9 psi to valve
positioner. valve positioner will supply o/p for 50 % valve
opening. the feedback arm of valve posioner will give
feedback to valve positioner according to valve position.

Answer / r_vaya

Valve Positioner actually working is following steps:
Supose valve is air to open and right now is at it's normal condition.at this condition positioner will not send any air to control valve.

Now given command to 10 percent to open 
So first positioner will send air strat to applying air to actuator ,when actuator will get sufficient air to perform operation it will start opening.
Now when the  valve will reach to the set point mean 10 percent,positioner will stop the air and maintain valve opening at a set point.
This thing is same in the closing

Thous positioner is works  to control the opening and closing .

 

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