| 摘要 |
PURPOSE: A screw-type dry vacuum pump is provided to prevent the accumulation of the reactive by-products in a pump. CONSTITUTION: A screw-type dry vacuum pump comprises a rotor(12) having a screw thread thereon for exhausting a gas through rotation, a casing(11) for housing the rotor therein, a reduced portion(14) provided in the casing, and an enlarged portion(21) 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 of the rotor.
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