OPERATION
SPECIAL PROCEDURES for CRYOPUMPING OXYGEN and OZONE
Be aware of the presence and concentration of oxygen and/or ozone in the process gases being
cryopumped. If oxygen concentrations exceed 20% (richer than in normal air), the cryopump
system must be constructed, operated and maintained according to oxygen manufacturer’s
standards. This includes materials of construction and approved vacuum pump oil for oxygen
service.
Cryopumping oxygen or ozone requires special precautions and frequent regenerations. Ozone
can react violently with charcoal. Daily regeneration may be required. Use an inert gas purge
during regeneration at a sufficient flow rate to minimize the explosion hazard.
Do not operate any ignition source (electric heaters, ionization gauges, etc.) in the cryopump
side of the high vacuum valve.
Be aware also that an ionizing process being cryopumped may produce ozone and create
explosive conditions.
Ozone can be identified by a “fresh air” odor as detected during a thunderstorm or pungent
odors similar to those from arc welding. Popping and/or cracking sounds, like from arcing or
welding, during regeneration indicate ozone’s presence.
If ozone is present:
a. Reduce the oxygen content in the process gas mixture to the lowest level allowable.
b. Follow all of the above precautions for oxygen. The cryopump must be regenerated daily.
Contact a SCAI Service Center if you have any questions.
Prestart Check
1. Check that the cooling water lines are connected. Turn on the coolant and check the lines
for leaks. Tighten fittings if necessary. See Specifications in the Compressor manual for
cooling requirements.
2. Check that all electric cables are connected:
a. Compressor power cable.
b. Cold head cable.
c. Remote on/off cable, if installed.
3. Check that the circuit breaker is closed.
4. When the compressor is at room temperature, 20°C (68°F), the pressure gauge(s) should
indicate the equalization pressure. See Helium Gas Pressures in the Specifications section
of the Compressor manual. Higher or lower temperatures will result in correspondingly
higher or lower pressures, but these pressure changes are normal. Abnormally lower
readings indicate that some of the gas charge has been lost. Refer to the Maintenance
section for instructions on charging, cleaning and leak checking.
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