Ulvac CRYO-U Series Instruction Manual page 16

3. Proceed with regeneration right
after the cryopump stops.
After stopping the cryopump operation, proceed with warm-up and rough pumping which
are parts of regeneration process in order to maintain the cryopump in a clean vacuum.
In many vacuum processes, a lot of moisture is often captured and condensed by the
cryopump. If the cryopump is left as it is after an operation stop, the captured moisture will
react with internal parts and cause corrosion. Moreover, when the corrosion of internal
parts becomes worse, it may bring about degradation of the pumping performance such as
prolongation of cooling time or rise-up of ultimate temperature as a result. Such corrosion of
inner kits occurs depending on not only moisture but also the kind and the amount of
process gas.
Therefore, make sure to perform regeneration immediately after the cryopump stops in
order to discharge water vapor. Following three steps in the regeneration sequence
mentioned in Section 6.4 are required; 1) Warm-up, 2) Discharge (desorption) of captured
gas, and 3) Pressure buildup check.
Please be aware that such corrosion of the inner kits might occur depending on the kind
or amount of the process gases, and note that when the part(s) needs to be exchanged due
to corrosion, part replacement is considered as fare paying service even if it is within the
term of a guarantee.
4. When pumping flammable or
explosive gases
Hydrogen is a typical gas which has flammability and explosiveness. When a
flammable or explosive gas is pumped with the cryopump, it must be exhausted
safely from the pump in the warm-up process of regeneration. Be sure to take the
following safety precautions.
(1). Control and manage the process condition, the time period and method of
regeneration in order to keep the concentration of the hazardous gases
discharged to the exhaust duct below an allowable value.
(2). Eliminate ignition factors completely from the pump and duct.
(3). Make sure that the safety precautions mentioned above can work well even in any
abnormal events.
Possible causes of ignition in the vacuum equipment are the followings:
Ignition by a vacuum gauge filament being turned on
Ignition by a heater with heating element(s) exposed into the process
circumstance or the like
S-4 ULVAC CRYOGENICS INCORPORATED