DSD sensors are single-acting pressure switches with a mechanical diaphragm. They are used to monitor pressure and vary in their set actuation pressure, electrical connection diagram, and dimensions. Under pressure, the plunger actuates the contact washer and moves it to the opposite contact, closing the electrical circuit. If the pressure decreases by the hysteresis value, the switch opens again. The normally closed contacts close in the opposite direction. In single-line systems, DSD sensors are integrated before the last metering device at the end of the lubrication line.