Maintenance Procedures
CTI-CRYOGENICS
HELIX TECHNOLOGY CORPORATION
properly connected and purged. This contamination 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.
Cold Head Decontamination Procedures
1.
Cool down the cold head and operate it for one to three hours. If
the system will not cool down, proceed to step 2. Operating the
cold head will isolate the contaminants by "freezing" them in
the cold head. The contaminants in the helium-gas circuit of the
cold head tend to become frozen inside the cold head. The
longer the cold head 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 compressor as follows:
a.
Close the Hi-Vac valve in your vacuum system.
b.
Turn off the system.
CAUTION
Exposing the cryopump to atmosphere during warm-up will cause
excessive water vapor adsorption by the charcoal of the 15K array.
3.
Immediately disconnect the helium-gas supply and helium-gas
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 (P/N 8080250K003) to the dis-
connected ends of the helium-gas return and helium-gas supply
lines.
5.
Reduce the pressure in the cold head to a level of 45 psig by using
the maintenance manifold.
6.
Allow the second stage of the cold head to warm up to room tem-
perature. Warm-up time can be reduced by purging the cryopump
with warm dry argon or nitrogen gas. Using the gas heater, CTI P/N
8080250K020, will reduce warm-up time about 50 percent, and
will maintain the gas temperature below the 150°F (66°C) limit.
7.
Once the cold head has reached room temperature, attach a two-
stage regulator (0-3000/0-400 psig) and charging line to a helium
bottle (99.999% pure). DO NOT OPEN THE BOTTLE VALVE AT
•
4-6
P/N 8040353
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