Abstract: A Roots pump rotates a plurality of rotors by a pair of rotary shafts to draw gas. Each rotary shaft extends through a rear housing member of the Roots pump. A plurality of stoppers are located on each rotary shafts to integrally rotate with the corresponding rotary shafts, and prevent oil from entering a fifth pump chamber of the Roots pump. A tapered circumferential surface is located about an axis of each rotary shaft. Each tapered circumferential surface is located adjacent to an end surface of the stopper and is closer to an oil zone than the end surface is. Each tapered circumferential surface is formed such that the distance between the circumferential surface and the axis of the rotary shafts increases from the side closer to the pump chamber to the side closer to the oil zone. This effectively prevents oil from entering the pump chamber.

Abstract: A compressor includes a compressing mechanism for compressing refrigerant gas and an oil separator for separating the oil from the gas. The separated oil is used to lubricate the compressor. The compressor has a discharge passage to permit refrigerant gas to flow out of the compressor, a recess located in the discharge passage, a plug press fitted in the recess and a supply passage for returning the separated oil to the compressor. The plug and the recess define a separation chamber having a circular cross-section and an annular chamber. The separation chamber is connected with the annular chamber by an outlet passage formed in the plug. The refrigerant gas swirls along the wall of the separation chamber, which separates the oil from the gas. Since the plug is press fitted in the recess, installation of the plug is facilitated. This structure also prevents the plug from loosening.