The pressure at port pressure of the monitored medium is - depending on the pressure range - on a flat membrane and operated via a lever system and springs on a cascade switch. It guarantees flutterfree switching. The switches operate independent of the position.

If there is no pressure on the membrane the contact 1-2 is closed. Pump or compressor may start.
If the set upper switching point is reached, contact 1-2 opens and contact 1-4 closes. Pump or compressor will be switched off.

Contact 1-2 will only be restored when the pressure on the membrane has dropped to the set lower switching point. The upper and lower switching point can be adjusted with a screwdriver independently. For each switching point, a scale exists.