Roots "Blower Fan" system belongs volume rotary blowers. This compressor rotor shaft by synchronized gears remain engaged so that the two rotors. The rotor and the cylinder inner wall surface of each concave portion is composed of working volume, during the rotation of the rotor away from the gas suction port, when moved to the vicinity of the exhaust port and an exhaust port communicating transient, due to the higher pressure the gas was refluxed, then the pressure in the working volume suddenly increased, and then supplied to the gas exhaust passage. Two rotors do not contact each other, the gap between them by a seal tightly controlled, so the exhaust gas from oil pollution.