Screw-type dry vacuum pump

摘要

A screw-type dry vacuum pump comprises a rotor having a screw thread thereon for exhausting a gas through rotation, a casing for housing the rotor therein, a reduced portion provided in the casing, and an enlarged portion provided on a discharge end of the casing. The reduced portion forms a slight gap between the outer circumferential surface of the rotor and the inner surface thereof. The enlarged portion forms a larger gap between the outer circumferential surface of the rotor and the inner surface thereof.