Operation
4. Allow the second-stage temperature to rise to at least 280 K for effective desorption of
gases from the charcoal.
EXPLOSION HAZARD. AVOID INJURY. Establish a cleaning schedule based
on pressure rise to keep the relief valve free of dirt generated during the vacuum
process.
In high-vacuum applications, as the cryopump warms up, the internal pressure may never reach
atmospheric pressure. In applications of cryopumps that pump a lot of gas onto the cryopanels,
the pressure increases slowly until the frozen gases melt, then pressure rises rapidly. Typically,
gas flows through the relief valve in less than a minute, then additional gas vents slowly as the
pump warms further. See Figure 15.
Figure 15 Warm Up the Cryopump
Regeneration: Purge Phase
For safety and accelerated warm up, the use of nitrogen to purge the cryopanels during warm
up is recommended. Inject warm, dry nitrogen gas directly onto the charcoal coating through
the N
2
purge port. Nitrogen purging hastens regeneration and displaces adsorbed gases from
the charcoal.
Nitrogen purging dilutes hydrogen, oxygen and other reactive or poisonous gases. Vent all
purged gases safely through the pressure relief valve to a suitable vent system. Nitrogen
purging should continue until the cryopump reaches room temperature. The operator should
determine the gases being cryopumped and safely vent toxic gases.
Only two methods of regenerating are recommended: nitrogen purge or nitrogen purge plus
heating the outside of the cryopump. Nitrogen purging and an outside heat source is the best
method for most high-vacuum systems because it cleans the cryopump effectively and rapidly.
Both methods require additional equipment that is not part of the standard cryopump.
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