The oil pressure switch is a safety device often used in refrigeration equipment control circuits, it is the control of oil pressure failure. Its application is basically in the protection of generally semi-hermetic compressor engines that use lubrication pumps, responsible for the oil circulation and consequently for the lubrication of the internal mechanical parts of this engine.
The oil pressure switch is always used in compressors with forced lubrication, checking the differential pressure of the oil pump. For this, it admits two pressure sockets: one of low pressure (LP) and the other of "high pressure" (HP or OIL). The HP / OIL side is connected to the oil pump outlet and the low side to the pump suction or compressor crankcase.
It has an internal differential pressure regulation that must be adjusted according to the specification of each compressor manufacturer. We should always remember that it works by checking that the compressor oil pump is working properly, there is any obstruction in its suction or if the compressor oil has been sent to the system and not returned to the crankcase. In all these cases we must safely stop the compressor.
Because it is a safety device, it must be reset manually, ie a mechanic must be present before resetting the compressor, checking the installation conditions and why the compressor has stopped.
Another important setting on an oil pressure switch is the delay time. This time is for the compressor to start and regulate the oil pressure. If after this time the differential pressure is still not within the standards, the system will be stopped by the pressure switch timer.
There are oil pressure switches that have an internal electronic timer, which allows the delay time to be adjusted from 20 to 150 seconds. Another very interesting feature is that they can be powered with a voltage range of 24 to 240 Vac / Vdc.
IMPORTANT: Particular care should be taken in the electrical connection of the oil pressure switch as it should be energized at the same time as starting the compressor. Such a procedure is recommended to avoid starting the time count before the compressor actually starts.
The most common defect when this care is not taken is that the compressor does not start because of the oil pressure switch but the lubrication conditions are all in perfect condition. To avoid this problem simply connect the pressure switch power supply to the same compressor contactor.
