Sumitomo Marathon CP-8 - Crossover Pressure Determination; Regeneration; Regeneration: Warm-Up Phase

Operation
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Because maximum refrigeration is produced when the full stroke length of the displacer is
utilized, it is normal for a very light tapping to occur when the unit is adjusted for minimum
temperature. The unit can be adjusted to reduce the tapping noise. However, this results in a
slightly shorter displacer stroke which causes a decrease in refrigeration produced and
therefore an increase in first- and second-stage operating temperatures.
Crossover Pressure Determination
Crossover is the pressure at which the isolating gate valve is opened to begin steady-state
cryopumping of the main vacuum chamber.
To determine the maximum crossover pressure, divide the crossover rating for the cryopump by
the volume of the main vacuum chamber.
Crossover Pressure (torr) < Crossover Rating (torr-liters)
Chamber Volume (liters)
The crossover rating for the Marathon
®
CP-8 Cryopump for air is 220 torr-liters. If the volume of
the main chamber is 220 liters, the crossover pressure should be 1 torr or less.
When a suitable crossover pressure has been reached, open the gate valve to expose the
cryopump to the main vacuum chamber. As a check, if the volume of gases in the main
chamber does not raise the second-stage temperature above 20 K, then the crossover pressure
is correct.
Regeneration
Regeneration removes the frozen, trapped gases from the cryopump and returns it to its full,
rated capacity. The process comprises four phases: warm-up, purge, evacuate and cooldown.
Because the time between regenerations depends upon the cryopump application, the user
must determine the most suitable interval. Cryopumps in many applications will operate two
weeks or more before regeneration becomes necessary.
Usually, regeneration is initiated when the second-stage temperature rises to 20 K, or when the
pumping speed decreases to 50% of its initial value. If the process flow is constant, the
pumping speed is one-half when the operating pressure doubles.
Regeneration: Warm-Up Phase
EXPLOSION HAZARD. AVOID INJURY. Use a fail-safe, automatic nitrogen
purge to immediately dilute toxic and flammable gases.
1. Close the gate valve to isolate the cryopump from the main vacuum chamber.
2. Stop the cryopump by stopping the compressor. If more than one cryopump is operating
from one compressor, see the section Shutdown: One Cryopump in a Multiple Cryopump
System.
3. Open the nitrogen purge valve. Gas will vent through the pressure relief valve.