It is necessary that there is a pressure difference between the valve inlet and outlet to ensure that solenoid valves of this design can open. In the technical data sheet the necessary min. pressure is defined as minimum pressure. Here the solenoid drive only fulfils a rough control function by which the main sealing element (diaphragm or piston) is released. The medium pressure and the existing pressure difference, respectively lift the sealing element. With this control type you can control high pressures with small solenoids and large nominal widths.