Ulvac CRYOPUMP CRYO-U Series Instruction Manual page 83

CRYO-U Cryopump Instruction Manual
®
Problem
Ⅴ．(Continued)
Pumping performance
of the cryopump is
lowered.
Possible cause
6) Performance of the refri-
gerator is deteriorated.
① Helium gas is heavily
contaminated.
② Helium filling pressure is
deficient.
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.
ULVAC CRYOGENICS INCORPORATED
Corrective action
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.
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.
A-5