A rotary compressor having mating rotary impellers defined by lobes and well spaces therebetween, a discharge port sealed by the peripheral surface of one of the lobes and passages for communicating one impeller well space with a well space of the other impeller as the discharge port is sealed by the one impeller peripheral surface. According to one form, the passages are defined by conduits in the compressor housing; whereas according to a second form the passages are defined by a recess in one impeller and the interior of the compressor housing.