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Contents
Cryopump
A vacuum cryopump typically consists of a vacuum-tight vessel with
a valved inlet, containing a highly absorbent material such as a synthetic
zeolite microporous on the scale of 1 to 10 Å (Angstrom units),
and an enclosing cryogenic vessel. In industrial
cryopumps, the vessel will typically be a Dewar flask, but homespun sorption
pumps may be as simple as a labglass flask of zeolite in a styrofoam cooler
filled with liquid nitrogen.
Sorption pumps are often used as roughing pumps to reduce pressures from the
range of atmospheric to on the order of 10-3 torr, while
lower pressures are achieved using a finishing pump (q.v. vacuum).
As the sorbent saturates, the effectiveness of a sorption pump decreases,
but can be recharged by heating the zeolite material (preferrably under
conditions of low pressure) to a temperature near but below the breakdown
point of the zeolite material's porous structure.
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