Ulvac CRYO-U Series, Instruction Manual

Page: 87 / 106

CRYO-U
®
Cryopump Instruction Manual
ULVAC CRYOGENICS INCORPORATED A-5
Problem
Possible cause Corrective action
Ⅴ．
(Continued)
Pumping performance
of the cryopump is
lowered.
6) Performance of the refri-
gerator is deteriorated.
①
Helium gas is heavily
contaminated.
②
Helium filling pressure is
deficient.
Perform decontamination
procedures described in Sec.8.5.
Use helium gas with purity of
99.999% or more.
Add helium gas with purity of
99.999% or more to the specified
value.
If no cause is found, contact our
Service Engineering Division or
the nearest CS center.
7) Performance of 15K cryopanel is
deteriorated.
①
Excessive water vapor
adsorption .
②
Since the roughing valve was
accidentally opened in the cold
condition of the cryopump, the
panel has been contaminated
with impurities gas.
③
Since rough pumping was
performed at 13Pa or less for a
long time using the oil-sealed
rotary pump, the panel has
been contaminated with oil.
Introduce dry nitrogen or argon and
repeat rough pumping.
Or, heat the cryopump with a band
heater or an inner heater (available
as option).
Replace 15K cryopanel. When an
oil-sealed rotary pump is used for
rough pumping, the panel may be
contaminated with oil.
Replace 15K cryopanel.
Be sure not to perform rough
pumping at 40Pa or less for a long
time.