Patent ID: 7950911

Claim:
A single stage root type-vacuum pump configured to perform normal rotation and reverse rotation, comprising: a casing having a suction port and a discharge port spaced apart from the suction port; a pair of three-lobe rotors located inside the casing and each having three lobes, the casing and the three-lobe rotors being configured to suck a fluid from the suction port and to discharge the fluid from the discharge port by a rotation of the pair of three-lobe rotors while avoiding communication between the suction port and the discharge port, wherein: the suction port is located in a position defined by a displacement angle of 120 or more degrees of a side between a center of a respective rotating shaft of each of the rotors and the suction port, relative to a phantom line connecting the center of each of the rotating shafts of the respective rotors, the discharge port is located in a position defined by a displacement angle of 120 or more degrees of a side between the center of each respective rotating shaft of each of the rotors and the discharge port, relative to a phantom line connecting the center of each of the rotating shafts of the respective rotors, two enclosed spaces are provided immediately downstream of the suction port, the enclosed spaces each being surrounded by adjacent lobes of a corresponding one of the three-lobe rotors, and being surrounded by an inner wall surface of the casing in a region between the suction port side and the discharge port side, and an outside air introduction hole is provided in a vicinity of the phantom line at a peripheral wall portion on a discharge port side of the casing, the hole having a horizontally long slit shape, and being oriented parallel to a width direction of the casing, and a check valve having an outside air introduction pipe connected to an outside air communication hole provided on a casing lid on the discharge port side of the casing, the check valve being configured to prevent fluid from flowing out of the casing during reverse rotation of the rotors.