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Electro Pneumatic Valve Positioner and Pneumatic Valve Positioner
The difference between Electro Pneumatic Valve Positioner and Pneumatic Valve Positioner
The pneumatic valve positioner works according to the principle of torque balance. When the signal pressure P1 entering the bellows 2 increases, the main lever 3 is rotated around the fulcrum, so that the nozzle baffle 9 is close to the nozzle, and the nozzle back pressure is passed through the one-way amplifier. 8 After zooming in, the pressure to the diaphragm chamber of the actuator increases, causing the valve stem to move down. And drive the feedback rod to rotate around the fulcrum, the feedback cam also rotates counterclockwise, the auxiliary lever 4 is rotated around the fulcrum through the roller, and the feedback spring is stretched, and the pulling force and signal pressure of the spring on the main lever 3 are used in the bellows. When the force on the meter reaches the moment balance, the meter reaches the equilibrium state. The valve position of the actuator is maintained at a certain opening degree, and a certain signal pressure corresponds to a certain valve position opening degree. The above action mode is positive action, if you want to change the action mode, you only need to turn the cam over, and the A direction becomes the B direction, etc. The so-called positive-action positioner means that the signal pressure increases and the output pressure also increases; the so-called reverse-action positioner means that the signal pressure increases and the output pressure decreases. As long as a positive-acting actuator is installed with a reaction positioner, the action of the reaction-action actuator can be realized; on the contrary, a reaction-action actuator can realize the action of a positive-action actuator as long as a reaction-action positioner is installed.
The electro pneumatic valve positioner is the main accessory of the control valve. It takes the stem displacement signal as the input feedback measurement signal, and uses the controller output signal as the setting signal for comparison. The output signal causes the actuator to act, and establishes a one-to-one correspondence between the displacement times of the valve stem and the output signal of the controller. Therefore, the valve positioner constitutes a feedback control system with the stem displacement as the measurement signal and the controller output as the set signal. The manipulated variable of the control system is the output signal of the valve positioner to the actuator.