Pneumatic Valve Positioner Working Principle

The pneumatic valve positioner works according to the principle of torque balance. When the signal pressure P1 into the bellows 2 increases, the main lever 3 is rotated around the fulcrum, and the nozzle baffle 9 is close to the nozzle, and the nozzle back pressure is amplified by the unidirectional amplifier 8. After that, the pressure into the diaphragm chamber of the actuator increases, causing the valve stem to move downward.

And drive the feedback lever to rotate around the fulcrum, the feedback cam also rotates counterclockwise, the secondary lever 4 is rotated around the fulcrum through the roller, and the feedback spring is stretched. The tension and signal pressure of the spring on the main lever 3 are used in the bellows. When the upper force reaches the moment balance, the instrument reaches the equilibrium state.

The valve position of the actuator is maintained at a certain opening, and a certain signal pressure corresponds to a certain valve opening. The above action mode is positive action, if you want to change the action mode, just flip the cam, A direction into B direction, etc., you can.

The so-called positive-acting positioner means that the signal pressure increases and the output pressure also increases; the so-called counteracting positioner means that the signal pressure increases and the output pressure decreases.

A positive-acting actuator can realize the action of a counter-acting actuator as long as it is equipped with a reaction positioner; on the contrary, a counter-acting actuator can realize the action of a positive-acting actuator as long as it is equipped with a counter-acting positioner.