| 摘要 |
<p>The present invention relates to a multi-stage vacuum pump having a plurality of compression stages 12, 14, 16, 18 20 and a booster stage 22. The pump 10 is arranged to pump a chamber 24. The pumping stages comprise respective rotors supported for rotation on one or more common drive shafts 26. A recirculation valve 28 is associated with the booster stage 22 for selective recirculation of pumped fluid from an outlet 32 to an inlet 30 of the booster stage above a predetermined pressure.</p> |
