Proportional valve, servo-assisted

Servo-assisted proportional valve
The Figure shows the operating principle of such a valve. When it is closed, the medium at the input side has a pressure of p1, the core or plunger (3) has dropped out and therefore presses on the pilot seat (4). As a result of this and the force of the piston spring, which acts on the piston (2), the main seat (5) is closed. A restrictor port (6) allows the medium to enter the control chamber (1) and press on the diaphragm or gasket from above with a pressure px.
If the restrictor port, pilot seat and area ratios on the main stage are rated accordingly, the compression forces on the piston reach equilibrium when the seat is opened by a certain position. With proportional pilot control, ideally, the piston follows the continuous axial movement of the plunger precisely at the distance that creates this equilibrium.