ROOTS VACUUM PUMP

A roots vacuum pump is provided to reduce noise generated during the operation and to promote low-temperature condition over the entire pump by preventing rapid pressure connection of an outlet side with outside air causing noise of explosion of compressed gas. In a roots vacuum pump, an inlet port(2) is disposed in a position(n) apart from the center of each rotary shaft(5,7) to an imaginary line(m) connecting each center of the rotary shaft of a rotor over a positive displacement angle of 120°. An outlet port(3) is disposed in a position(o) apart from each center of rotary shaft to the imaginary line over a positive displacement angle of 120°, at the opposite side of the inlet port. A closed space is defined on the inlet port and the outlet port by an inner wall of a casing and a laminar adjacent each rotor right after the suction of air. An outside/cooled air feed port(8) is contoured on a position(t) apart from the position(o) by 90°. A plurality of discharge grooves(10) is contoured on the inner wall of the casing in an area from the position(o) to a position(u) apart from the position(o) by 45°, in communication with the outlet port.