| 摘要 |
<p>PURPOSE:To enlarge pressure ratio between pump stages by providing a flow path for introducing gas different from gas introduced from an intake port of a vacuum pump to at least one stage downstream of the intake port. CONSTITUTION:A pipe 18 is provided for a flow path connecting a fixed disk 12B at the first stage of circumferential flow compression pump stages 12 of a molecular pump to a housing 2 so that gas having large molecular weight like nitrogen and air can be introduced from the outside of the housing. When gas introduced from an intake port 2A has small molecular weight and the gas having large molecular weight is injected through the pipe 18, then the pressure ratio at said stages 12 can be sufficiently enlarged to reduce pressure at the intake port.</p> |
