Ulvac CRYOPUMP CRYO-U Series Instruction Manual page 81

Troubleshooting
Problem
(Continued)
Ⅴ．
Pumping performance
of the cryopump is
lowered.
Examples
・Temperature is higher
than the normal value.
・Pumping speed is
falling.
･ Vacuum
level has
worsened.
･ Helium
gas filling
pressure is lower than
the specified value.
A-4
Possible cause
4) Failure of the refrigerator unit or
the compressor unit.
1) The ultimate pressure of the
vacuum chamber after roughing is
still high.
2) A large amount of gas has been
captured.
3) High partial pressure of helium
remained in the cryopump.
4) Leakage
① Air-to-vacuum leakage at
attaching parts or ports on the
cryopump.
② Helium leakage caused by the
slack of helium gas joint.
5) Internal equipments of the
cryopump becomes loose in
the following parts:
① Thermometer mounting bolts.
②Mounting bolts of 80K shield,
80K baffle, and 15K cryopanel.
ULVAC CRYOGENICS INCORPORATED
Corrective action
Contact our Service Engineering
Division or the nearest CS center.
Rough pump to
allowable crossover pressure or less
(Recommended value: 40Pa). Refer
to Sec. 5.6 for details.
Regenerate the
described in Sec.6.
Purge helium with dry nitrogen gas to
reduce the partial pressure of helium.
Detect the leakage by the evacuation
method using a helium leak detector
or mass analyzer, and stop the
leakage.
Detect the leak point by Sniffer
method using a helium leak detect
or or by the bubbling method with
soap, and stop the leakage.
If no leak is found, contact our
Service Engineering Division or the
nearest CS center.
If necessary, disassemble
cryopump and
temperature sensing part firmly to the
second stage of the refrigerator unit.
Replacement of the indium sheet is
required.
If necessary, disassemble the
cryopump and retighten all screws.
Replacement of the indium sheet
is required.
the maximum
cryopump as
the
remount the