Cryo-Torr High-Vacuum Pump Installation, Operation and Maintenance Instructions
P/N 8040613
5-1
C
HELIX TECHNOLOGY CORPORATION
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TI
CRYOGENICS
Section 5 - Maintenance Procedures
Helium Circuit Decontamination
Contamination of the helium-gas circuit is indicated by sluggish or
intermittent operation (ratchetting) of the cold head drive mechanism. With
severe contamination the cold head drive may seize and fail to operate. One
of the major sources of contamination is using helium gas of less than the
required purity. When performing the decontamination process, use only
99.999% pure-helium gas, and the regulator and charging line must be
properly connected and purged.
This decontamination procedure will remove contaminants from the cold
head and/or compressor, thereby restoring system performance. The cold-
trapping of contaminants inside the cold head during this procedure will
also decontaminate the compressor if the contamination of the system is
not severe. Separate decontamination of the compressor is required
whenever the compressor has been opened to atmosphere, or the pressure
dropped to zero.
Cryo-Torr Cryopump Decontamination Procedures
NOTE: Refer also to the appropriate Compressor Manual.
1. Cool down the cryopump and operate it for one to three hours.
If the system will not cool down, proceed to step 2. Operating
the cryopump will isolate the contaminants by "freezing" them
in the cold head. The contaminants in the helium-gas circuit of
the cryopump tend to become frozen inside the cold head. The
longer the cryopump is operated beyond the one-hour period,
the greater is the amount of contamination that becomes
isolated inside the cold head.
2. Shut down the cryopump as described in Section 2 - Installation.
3. Immediately disconnect the helium supply and return lines from the
gas-supply and gas-return connectors at the rear of the compressor.
Leave them attached to the cold head.
4. Attach the maintenance manifold to the disconnected ends of the
return and supply lines.
