CPC F04C 25/02 (2013.01) [F04C 18/126 (2013.01); F04C 23/001 (2013.01); F04C 28/26 (2013.01); F04C 29/0085 (2013.01); F04C 2220/12 (2013.01); F04C 2240/102 (2013.01); F04C 2240/20 (2013.01); F04C 2240/40 (2013.01)] | 14 Claims |
1. A pump unit comprising:
a rough-vacuum pump; and
a Roots vacuum pump connected in series with and upstream of the rough-vacuum pump in a direction of flow of pumped gases,
wherein the Roots vacuum pump has three pumping stages in which the rotors are configured to be driven simultaneously in rotation by a motor of the Roots vacuum pump, and
wherein a ratio of a flow rate generated by a first pumping stage of the rough-vacuum pump in the direction of flow of the pumped gases over a flow rate generated by a last pumping stage of the rough-vacuum pump is less than or equal to four.
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