Differential valves are used on low pressure oil return systems of refrigerating and air conditioning installation.
They are mounted on oil receivers in which they maintain a permanent overpressure compared to the compressor crankcases in order to ensure them a constant oil distribution. This is the guarantee of a regular and permanent oil reintegration.
Therefore, the oil which is returned to the compressor crankcases 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.
