The working principle of the pneumatic valve positioner
Pneumatic valve positioner is the main control valve accessories, according to the moment balance principle of work, it will stem the displacement feedback measurement signal as input, as set in the controller output signal, comparing, when there is deviation, change of its output signal to the actuator, the actuator movement, the valve stem is established displacement times and one to one correspondence relation between the controller output signal. As a result, the displacement of valve locator to stem for measuring signal, set in the controller output signal of the feedback control system. The control system of the control variables are valve locator to the output signal of the actuator. When the input signal increases, the torque motor to produce electromagnetic fields, baffle by the electromagnetic force away from the nozzle. Nozzle and baffle spacing, eliminate internal pilot valve spool above atmospheric pressure. Affected by the spool to move to the right, and promote block base valve core, air pressure through the base input to the actuator. As the actuator gas indoor pressure increases, executive mechanism in lowering, through feedback lever actuators push rod displacement change communicated to skateboard. The displacement change and convey feedback to the range pole, pull the spring range. When range spring force and torque motor to keep balance, baffle back in situ, decrease and nozzle spacing. With the decrease of the through the nozzle exhaust air volume, pressure increases above spool. Spool back to the in situ, the valve core to plug base, stop input air pressure to the actuator. When the movement of the actuator is stopped, the locator remain in a stable condition.