| 摘要 |
PROBLEM TO BE SOLVED: To provide an evacuation device having high energy efficiency when pressure on an intake side is in ultimate pressure or in a vacuum state in a certain extent, by reducing power by differential pressure. SOLUTION: The evacuation device 100 comprises of a roughing vacuum pump B and a booster pump A. Both the roughing vacuum pump B and the booster pump A are constituted of a screw vacuum pump and the design pumping speed of the roughing vacuum pump B is sufficiently smaller than that of the booster pump A, but in a degree that the roughing vacuum pump B can function as a roughing vacuum pump. The number of turns in a screw of the booster pump A is set smaller than that of the roughing vacuum pump B.
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