Welch Vacuum 1376N Chemstar - Manual (Page 30)

When pumping ozone, keep the concentration passing into the pump below 100 ppm. This can be accomplished either
by miniaturizing the experimental process to reduce the quantity of ozone used or by dilution of the ozone fl ow by dry
nitrogen.
Ozone is well known for chemically attaching vacuum pump oil. DIRECTORR gold oil used in a CHEMSTAR is a highly
saturated oil that resists this attack. However you need to monitor the oil closely. An oil fi ltration system may be need
if you are seeing rapid degradation of the oil at the 100 ppm. A cellulose element should be used with the oil fi ltration
system (See Section 2 C. for more details on oil fi ltration system available from Welch).
If you will be pumping ozone at levels above 100 ppm of gas fl ow, you must switch to a perfl uoropolyethers such as
Fomblin Y06/6 (Welch Cat. No. 1408C-06, 1 Kg) - Fomblin is a registered trademark of Ausimont. Perfl uoropolyethers are
very resistant to chemical attack by ozone.
CAUTION
Failure to use Fomblin Y06/6 in applications where ozone is pumped
at concentrations above 100 ppm will lead to rapid degradation of the
DIRECTORR gold oil and CHEMSTAR pump failure.
To switch from DIRECTORR Gold oil To Fomblin, the CHEMSTAR pump must be totally disassembled and all parts
cleaned of oil. The pump must then be assembled using Fomblin. Welch can carry out the conversion for you through our
repair department. Call our factory at 847-676-8800 ext. 1 for details.
G. Anhydrides: SO
X
- Sulfur Trioxide (SO
3
) and Sulfur Dioxide (SO
2
), Hydrogen Sulfi de (H
2
S)
These gases in the presence of water have the same corrosive characteristics as the strong hydrous acids. The same
recommendations for strong acids are applicable to the anhydrides in the presence of water.
H. Fragments of Sulfur Hexafl uoride (SF
6
), Carbon Tetrafl uoride CF
4
) etc.
Sulfur hexafl uoride is a stable molecule except those gas cylinders of it normally contain variable quantities of low sulfur
fl uorides. These low sulfur fl uorides can hydrolyze in the presence of water to form hydrogen fl uoride (HF) - a compound
notorious for its toxicity and ability to corrode. Carbon tetrafl uoride (Freon 14) is also somewhat stable except that it
reacts with aluminum - CHEMSTAR pump oil cases are made of aluminum, but are PTFE lined.
Carbon tetrafl uoride is soluble in oil so the pump should be allowed to run for 10 to 15 minutes prior to pumping this
gas. This will allow the pump to reach it operating temperature. When the pump is at its operating temperature, this will
minimize the effect on a rise in ultimate pressure due to the presence of carbon tetrafl uoride in the oil. Also, the gas-
ballast should be opened during operation to also help keep carbon tetrafl uoride at a minimum in the oil.
Sulfur hexafl uoride and carbon tetrafl uoride are commonly run through electrical or microwave discharges to create highly
reactive radicals. These radicals can be extremely corrosive in their own right but in the presence of water can turn into
hydrogen fl uoride (HF).
I. Special Note: Pumping oxygen
Whenever mixtures containing oxygen or pure oxygen are used a nonfl ammable vacuum pump oil such as Fomblin Y06/6.
DIRECTORR Gold is a synthetic saturated hydrocarbon oil and is fl ammable.
WARNING
Do not use DIRECTORR gold oil when pumping gases containing more than
30% oxygen. The use of DIRECTORR gold which is supplied with the pump is
a Flammability Hazard if more than 30% oxygen mixtures are pumped.
When gases pumped into a CHEMSTAR pump exceed 30% oxygen of gas fl ow, the CHEMSTAR pump must be prepared
with FOMBLIN Y06/6 (Ausimont registered trademark). Contact the Welch factory for advice or to have your CHEMSTAR
pump prepared with FOMBLIN Y06/6 if you will be pumping greater than 30% oxygen gas fl ows.
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