• Differential valves are mounted on refrigerating and air conditioning installation oil receivers.
• They maintain permanent oil receiver overpressure versus the compressor sumps in order to ensure constant oil distribution to the compressors.
• Therefore, the oil which is returned to the compressor sumps is free from refrigerant as, should any refrigerant come from the oil separator, it would be expanded in the oil receiver and drained out to the suction line via the differential valves.