Solenoid valves of this type require a pressure difference between the valve inlet and the valve outlet in order to open.
The minimum pressure required is specified as the minimum pressure in the technical data sheet. The solenoid actuator only fulfils a pilot function here, which relieves the main sealing element (diaphragm or piston). The medium pressure or the existing pressure difference lifts the sealing element.
With this type of control, small solenoids can be used to control high pressures with large nominal diameters.
All servo-controlled solenoid valves: