Ulvac CRYOPUMP CRYO-U Series Instruction Manual page 72

Maintenance
8.5. Helium Circuit Decontamination
The equipments for charging helium gas (regulators, charging hoses, adopters) that can be
used at 2.0MPaG or above are required for this work.
When helium gas in the cryopump system is contaminated, it is necessary to replace the gas
in the system with pure helium gas.（Refer to Appendix A- Troubleshooting.）
Contamination of helium gas in the cryopump system is caused by inadequacy of helium
charge at the time of refrigerator unit maintenance. If impurities in helium gas are
coagulated and deposited into the refrigerator, the performance of refrigerator could be
deteriorated and abnormal vibration of the motor (called Step-out※) may occur. Please
execute decontamination of the gas by the following method.
※ Step-out: means that a refrigerator motor has an irregular or intermittent movement.
１．Turn on the cryopump system (refrigerator unit) and keep the running for three to four
hours.
NOTE:
Since all impurities in the helium gas are condensed and solidified within the refrigerator
during operation of the cryopump (refrigerator), a certain amount of cooldown time is
required before beginning the decontamination procedures. If an irregular and abnormal
sound or a big vibration arises during the operation, proceed to the next step (2).
２．Shut down the cryopump (refrigerator unit) as follows:
ａ．Close the main valve of your vacuum system.
ｂ．Turn off the compressor unit.
３． Right after shutdown of the system, disconnect the helium SUPPLY and RETURN flexible
hoses at rear of the compressor unit. (See Figure 8-2.)
NOTE:
It is important to remove the flexible hoses right after shutdown in order to prevent
re-diffusion of the impurities that have been coagulated in the refrigerator unit.
４．Attach the charging adaptor to the disconnected end of the helium SUPPLY and RETURN
flexible hoses.(See Figure 8-3)
8-8 ULVAC CRYOGENICS INCORPORATED