Ulvac CRYOPUMP CRYO-U Series Instruction Manual page 19

Inert gas
I N
Figure 2 Dilution of Oxygen/Flammable Gas
(1) Whenever a cryopump stops, it is required to perform assisted regeneration
immediately to remove flammable, explosive or oxidizing gases from the cryopump
regardless of the cause of shutdown.
temperature of below -40ºC or argon as the inert gas. (In this book, the terms "inert
gas" or "dry nitrogen or argon" mean "nitrogen gas with dew point temperature of
-40 ºC or below or argon".)
Both the purge of the cryopump and the dilution of the exhaust duct with the inert
gas are required to reduce the concentration of hazardous gas and keep it under a
certain level where the gas does not burn or explode even when it evaporates
during warm-up.
Fix the purge flow rate, dilution flow rate, and regeneration cycle (pumping capacity
of flammable gas) and take necessary safety measures before starting cryopump
operation.
(2) When the above regeneration is delayed or is not conducted, all the gases captured
in the cryopump will evaporate by natural temperature rise. If the volume of such
gases is large, cryopump pressure may easily reach or exceed the atmospheric
pressure. Note that a roughing pump should not be used to pump such hazardous
gases remaining inside the cryopump as it may lead to gas explosion.
In order to exhaust the vaporized gases from the cryopump safely, make sure
to purge the cryopump with inert gas before initiating vacuum pumping.
(3) Eliminate ignition factor. Insure that there are no sources of ignition (refer to "4.
When pumping flammable or explosive gases") on the cryopump side during
Chamber
C h a m b e r
OUT
CRYO-U®
R
C RY O - U
Pressure relief valve
ULVAC CRYOGENICS INCORPORATED
Exhaust line
- Use metallic pipe and grounding.
- Determine the pipe diameter that can
prevent the pressure loss, considering the
length to the outside.
O u t d o o r
Outdoor
Inert gas
Use nitrogen gas with dew point
S-7