The oil pressure switch acts as a function of the differential pressure, which is obtained through the use of two diaphragms or bellows in their physical constitution. One bellows is connected to the crankcase reflecting the pressure thereof, while the other is connected to the discharge of the oil pump, the pressure difference between the two bellows is the differential pressure, used to drive a differential pressure switch in the pressure switch.
An operating relay incorporated into the pressure switch allows the compressor to operate from 90 to 120 seconds with the pressure below the minimum safety level. This allows the compressor to start with zero oil pressure and also prevents unnecessary shutdowns in case of momentary pressure drops.
The oil pump operates only when the compressor operates, the total oil pressure will be exactly equal to the sump pressure during a rest period of the compressor, ie when the compressor is switched off the crankcase pressure equalizes with the pressure of discharge the pump.
However, if the pressure does not rise within the preset time, the pressure switch will turn off the compressor and before the compressor can be restarted the pressure switch must be manually reset.
