Ulvac CRYO-U Series Instruction Manual page 23

9. Do not charge the system with excessive helium gas
In our cryopumps, high-pressure helium gas is circulated in the system to get an effective
refrigerating cycle. Charging with helium gas more than the specified value does not
enhance the performance of refrigerator. Conversely, if the helium gas pressure exceeds the
specified value, the pressure relief valve could be open, and it would bring about the trouble
of air leakage because particles would stick to the vacuum seal in the valve. Moreover, the
excessive high-pressure gas might cause another trouble that the system would stop by
hitting the high-pressure switch in the compressor unit.
Do not charge the refrigerator with helium gas exceeding the regulated value.
10. Power source of cryopump system
Refer to the instruction manual of the compressor unit to be utilized with the cryopump,
and confirm the power source required for the system.
① Make sure to connect the earth wire to a ground terminal.
Earth : D-class grounding with the ground resistance of 100 Ω or less.
② Install ground-fault interrupter on the electric supply line for the compressor unit.
③ Do not connect any devices except a cryopump system on the outlet of the ground-fault
interrupter.
ULVAC CRYOGENICS INCORPORATED S-11