Pressure switch

Pressure switches are mechanical or electronic switches which are actuated by changes in pressure of a gaseous or liquid medium, for example air or hydraulic oil.

They are used among other things to switch pumps, valves or compressors so that the pressure or level of the medium in an accumulator tank or an upper value does not exceed, and a lower value does not fall below.

The simplest and most common principle of a mechanical pressure switch is based on a metal diaphragm which expands with increasing pressure and opens the switch contacts about this movement. A switched on the pump pressure switch thus turns off with a defined pressure. The metal membrane is typically applied by a coil spring with a counter- pressure at the pressure falls, the expansion goes back and the switch contacts are closed ( the pump turns on, the container is filled ). The spring is adjustable in preload, what can be set the start and stop. Usually this difference of the power-on to switch-off (the hysteresis ) remains constant.

Mechanical pressure switches have a relatively large difference (hysteresis) between the upper switching point and the lower reset point. This is partly desirable because it offers the simple two-point controller with no rules set up. To mechanical pressure switches, the amount of hysteresis (? P ) can usually be adjusted by a further spring mechanism.