The oil pressure switch is a safety device frequently used in the control circuits of refrigeration equipment, it is the control of oil pressure failure. Its application is basically in the protection of generally semi-hermetic compressor motors that use of lubricating pumps, responsible for the circulation of the oil and consequently for the lubrication of the mechanical parts internal of this motor.
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 points: one of low pressure (LP) and the other one of high pressure (HP). The HP side is connected to the oil pump outlet and the low side to the pump suction or to the compressor sump.
It has an internal regulation of the differential pressure that should be adjusted according to the specification of each compressor manufacturer. We must always remember that it works by checking if the compressor oil pump is in good condition, or if there is no obstruction in its suction. We still have the case where the compressor oil was sent to the system and did not return to the sump. In all these cases we must for safety stop the compressor.
Because it is a safety equipment, it is manual resetting, ie it is necessary to have a mechanic present before re-starting the compressor, check the conditions of the installation and the reason the compressor has stopped.
Another important setting in an oil pressure switch is the delay time. This time is used for the compressor to start and regulate the oil pressure. If after this time the differential pressure is not yet within the standards, the system will be stopped by the pressure switch timer.
Some oil pressure switches have an internal electronic timer, which allows the delay time to be set from 20 to 150 seconds. Another interesting feature is that they can be supplied with a voltage variation of 24 to 240 Vac / Vdc.
IMPORTANT: Particular care must be taken in the electrical connection of the oil pressure switch, since its energization must be simultaneous at the start of the compressor. This procedure is recommended to avoid starting the time counting before the actual start of the compressor.
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 turn on the pressure switch to the same compressor contactor.
