Crossover - Ulvac CRYO-U Series Instruction Manual

Operation
２． When the pressure of vacuum chamber has reached 40Pa, close the roughing valve
（RV2）and then turn off the roughing pump.
If you use an oil-sealed rotary pump as a roughing pump, and rough pumped for a
long time at the pressure of 40Pa or less, it is rec
the rough pumping line.
To determine the crossover pressure, refer to Section 5.6.
Open the main valve（V1）
３．
When the pressure of the vacuum chamber has reached t
４．
with vacuum process such as deposition or sputtering. The time required t
the intended pressure depends on the volume, contents, and the wall conditions of
the chamber, etc.
If the abnormal rise of the pressure in the
cryopump case may dew. It may cause short-
cryopump. Be careful about the operating condition of equipment, and surrounding safety.
5.6

Crossover

Crossover pressure is pressure (roughing pressure) of the vacuum chamber immediately
before opening the main valve to evacuate the vacuum chamber by cryopump after
roughing the vacu
called the maximum allowable crossover pressure. The moment the main valve is opened,
the gas of the vacuum chamber is flowed into the cryopump and evacuated, but when the
flow rate of the gas exceeds the limit, cryopump cannot restore its evacuation performance,
and it gets hot and expels the gas evacuated so far.
The maximum allowable crossover pressure can be obtained by the following formula.
[Crossover Pressure Calculation]
Maximum allowable crossove
pre ssure (Pa )
5-4
for fine pumping the chamber by the cryopump.
um chamber. The maximum allowable roughing pressure in this case is
Max. quantity of sucked gas instantaneously
processable (Pa•L)
r
≦
ULVAC CRYOGENICS INCORPORATED
ommended to add a fore-line trap in
he required value, proceed
CAUTION
chamber break s out during operation, the
circuit if an elec trical device is put under the
Volume of vacuum chamber (L)
o reach