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Next, we will use the YT-1000R electrical positioner (E/P) as an example to explain the air circuit conversion and positioning principle of valve positioners. As shown in Figures 1 and 2, they are the structural diagram and the schematic diagram respectively. file:///C:/Users/S/AppData/Local/Temp/msohtmlclip1/01/clip_image002.pngfile:///C:/Users/S/AppData/Local/Temp/msohtmlclip1/01/clip_image004.pngfile:///C:/Users/S/AppData/Local/Temp/msohtmlclip1/01/clip_image006.jpg1. As shown in the diagram, the valve actuator is a double-acting type. First, air supply enters the pilot valve at ④, as indicated by the red arrow. The component marked with a circle is the valve spool, one on each side, connected to springs. When the air supply is activated, the gas passing through the middle of the pilot valve causes the shaft at ⑤ to move to the left. The valve spool on the left side is pushed away from the base at ⑦, allowing air to flow into the cylinder via OUT2, thereby closing the valve. file:///C:/Users/S/AppData/Local/Temp/msohtmlclip1/01/clip_image008.jpg2. When the current signal is increased, ①an electromagnetic field is generated in the coils of the torque motor, which causes ②the baffle to be subjected to an electromagnetic force and move to the left, thereby moving away from ③the baffle. As a result, ④the gas inside the pilot valve can be discharged, and ⑤the shaft moves to the right to return to its original position; this causes the ⑧valve element on the right side to be pushed away from ⑦the base, allowing the OUT1 air path to become open ； At the same time, the gap between the valve core on the left and the base decreases, resulting in a reduced air supply. When the current signal is 20MA, the OUT2 air path is closed, air flows into OUT1, and the valve is fully open. 3. As shown by the action of the springs on both sides of the baffle, when the current signal decreases, it also causes the baffle to move away from the nozzle, thereby enabling a change in the air path and prompting the valve to operate. It is worth noting that the left spring is connected to the zero-point adjustment, while the right spring is connected to the range adjustment and feedback mechanism; ultimately, adjustment is achieved through the principle of force balance. 4. Discussion on the interchangeability of OUT1 and OUT2. Due to various practical issues that arise during the maintenance of instruments on-site, when the connection between the valve cylinder and its base is reversed, we generally consider swapping the OUT1 and OUT2 air circuits in order to enable the valve to function properly. However, due to the cam in the feedback section, it can only rotate 90° counterclockwise or clockwise. When rotating counterclockwise and the valve is fully open, the current signal is 20MA; the OUT1 air path is open while the OUT2 air path is closed. At this point, the cam has rotated counterclockwise to its edge and can only rotate clockwise. At this point, the gas path is switched: the OUT1 path is closed, the OUT2 path is open, all valves are closed, and the cam returns to its original position clockwise. As shown in the figure, a force analysis of the baffle indicates that it is not possible to interchange the OUT1 and OUT2 air paths in order to switch between forward and reverse operations; however, this can be achieved by replacing the cam with one that rotates clockwise or counterclockwise. file:///C:/Users/S/AppData/Local/Temp/msohtmlclip1/01/clip_image010.jpg