HELIX CTI-CRYOGENICS CRYO-TORR 100 Installation, Operation And Servicing Instructions page 29

5.9 Determining the Number of
Crossover Cycles
The number of crossover cycles between regenerations
can also be easily calculated when the crossover pressure
and vacuum chamber volume are known:
760,000 torr liters
N
= - - - - - -
PxV
N = Number of crossover cycles
V = Volume ofvacuwn cluJmber (liters)
P
=
Pressure ofvacuwn chamber prior to crossover
(torr) (roughing pressure)
Example:
For a vacuum chamber of 100 liters and a roughing
pressure of 1.5 torr, the number of crossover cycles
between regenerations would be:
760,000 torr liters
N
= - - - - - -
= 5,060 cye/es
15 (torr)
X
100 (liters)
5.10 Cryopump Shutdown
Procedures
Typically a cryopump can be left in operation
continuously if you are not processing or not using the
vacuum chamber, by simply closing the Hi-Vac valve to
isolate the cryopump from your vacuum chamber. You
are now able to load, unload, repair or replace
components in the chamber and the cryopump will be
available for restart of the process as necessary.
If
you are planning to shut down the cryopump it is
recommended that the cryopump be shut off and a gas
purge be initiated and continued until the cryopump has
reached room temperature. At this point it can be held
under positive pressure, and rough pumped prior to
startup.
5-5/5-6
eTi-CRYOGENICS
HELIX TECHNOLOGY CORPORATION
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5.11 Cryopump Storage
If the cryopump is stored while still attached to your
vacuum system, the cryopump vacuum vessel should be
kept at slight positive atmospheric pressure with
dry
nitrogen or argon.
If the cryopump is removed from your vacuum system,
install the protective cover on the mounting flange of the
cryopunip vacuum vessel inlet before storage.
The remaining components of your Cryo-Torr high-
vacuum pump systems are fully protected during storage
if kept under positive helium pressure and all component
connections left connected. Periodically check the
helium supply pressure gauge on the compressor.
If
the
gauge reads below 245 psig (1690 kPa) or 220 psig
(1515 kPa) for CT
-lOOn,
add helium as described in
Section 7.4, page 7-2.
5.12 Hazardous Materials
AWARNING
If the cryopump has been used to pump toxic or
dangerous materials, you must take adequate pre-
cautions to safeguard personnel.
If
such a cryopump
is shipped to a Product Service Department, clearly
mark on all storage cartons the identity of the toxic or
dangerous materials to which the cryopump has been
subjected. All shipped equipment that contains
hazardous/toxic materials must conform to DOT
regulations.