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2.8.1.2 Holweck stage operating principle<br />
A Holweck stage is a multi-stage Gaede‘s type molecular pump [10] having a helical pump<br />
channel. Due to the rotation of the rotor, gas molecules entering the pump channel receive a<br />
stimulus velocity in the direction of the channel. Backflow losses occur through gaps between<br />
the webs that separate the Holweck channels from one another and the rotor. The gap widths<br />
must be kept small to minimize backflow. Cylindrical sleeves (1) that rotate about helical<br />
channels in the stator (2) are used as Holweck stages. Arranging stators both outside as well<br />
as inside the rotor enables two Holweck stages to be easily integrated within one and the<br />
same pump.<br />
2<br />
Pumping speed<br />
Helium<br />
Nitrogen<br />
1<br />
a b h<br />
Figure 2.21: Operating principle of a Holweck stage<br />
Hydrogen<br />
Figure 2.20: Pumping speed as a function of inlet pressure<br />
Inlet pressure<br />
1) Rotor<br />
2) Stator with threads<br />
Page 61<br />
<strong>Vacuum</strong><br />
<strong>Technology</strong>
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