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System Overview
40
5.1.11 Vacuum System
During manufacture, the vacuum chambers are evacuated and baked to remove water vapor. The vac-
uum system is then permanently sealed off to prevent any air entering the system and to remove the
possibility of accidental loss of vacuum. The Liebert FS does not require an external vacuum pump to
maintain a suitable vacuum level; the vacuum system instead relies on absorbers to maintain a rough
vacuum within the upper chamber. A zero-maintenance molecular drag pump acts with the flywheel
shaft to maintain a high-vacuum in the lower chamber, as shown in Figure 41. Vacuum levels of
much less than 100 microTorr (10-7 atmosphere) are maintained in the lower chamber. The absorber
material only needs to be recharged or changed, once every 15 years.
Figure 41 Vacuum system operation
Air and Water Vapor
Upper Chamber
Rotating Shaft
Lower Chamber
Molecular Drag Pump
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