Abstract: A compressor has a crankshaft, at least one cylinder, and at least one piston. Each such piston is positioned for reciprocal motion at least partially within associated such cylinder and coupled to the crankshaft so as to drive the reciprocal motion. The compressor includes an inlet, a suction plenum, an outlet, a sump, and a valve between the sump and suction plenum. The valve may provide a desired discharge of refrigerant from a sump oil accumulation while controlling sump pressure and loss of the oil.