MEMBRANE SERVOMOTOR MECHANISM

When the pressure acting on membrane 1 increases, link 3 moves downward, compressing spring 2, and lowers rod 4 which is rigidly attached to rod 5. This reduces the amount of fluid passing through the openings of plunger 6. When the pressure acting on membrane 1 decreases, the amount of fluid admitted by the regulating member increases.
$4121$EHP,Dr$