Structural principle of pneumatic valve positioner

The pneumatic valve locator works according to the principle of torque balance. When the signal pressure P1 that enters the bellows 2 increases, the main lever 3 rotates around the fulcrum, making the nozzle baffle 9 close to the nozzle. After the nozzle back pressure is amplified by the unidirectional amplifier 8, the pressure that enters the diaphragm chamber of the actuator increases, causing the valve stem to move downward. And it drives the feedback rod to rotate around the fulcrum, and the feedback cam also rotates counterclockwise. The auxiliary lever 4 is rotated around the fulcrum through the roller, and the feedback spring is stretched. When the tension of the spring on the main lever 3 is balanced with the force of the signal pressure applied to the bellows, the instrument reaches a balanced state. The valve position of the actuator is maintained at a certain opening, and a certain signal pressure corresponds to a certain valve position opening. The above mode of action is positive. To change the mode of action, simply flip the cam to change the direction from A to B, etc. The so-called positive action locator means that as the signal pressure increases, the output pressure also increases; The so-called reaction locator refers to an increase in signal pressure and a decrease in output pressure. A positive action actuator can achieve the action of a reverse action actuator as long as it is equipped with a reverse action locator; On the contrary, a reverse action actuator can achieve the action of a positive action actuator by installing a reverse action locator.