Welch Vacuum 1376N Chemstar - Manual (Page 29)

29
C. Halogens: Chlorine (Cl
2
), Bromine (Br
2
).
If water is not present, small gas fl ows of chlorine or bromine can be pumped without major diffi culty. Welch recommends
that when dry chlorine and bromine occupy less than 5% of the total gas fl ow the gas ballast should be opened.
DIRECTORR Gold oil will work well for this gas load.
If the fl ow of dry chlorine or bromine exceeds 5% of gas fl ow, Welch recommends you dilute the chlorine or bromine by
adding dry nitrogen to the stream (See Section 3 B.). The dilution needs to bring the dry chlorine or bromine gas fl ow
back below 5%.
If the fl ow of dry chlorine or bromine cannot be brought below 5% of gas fl ow but is not above 10%, Welch recommends
that our oil fi ltration system with an alumina element be used (See Section 2 C. for information on the oil fi ltration system.)
If the fl ow of dry chlorine or bromine goes above 10%, 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 halogens.
CAUTION
Failure to use Fomblin Y06/6 in applications where chlorine or bromine is
pumped at concentrations above 10% of gas fl ow will lead to degradation of the
DIRECTORR gold oil and to the CHEMSTAR pump failing.
If the fl ow of chlorine or bromine is not dry (for example chlorine or bromine in humid air), hydrochloric and hydrobromic
acid will appear in the gas stream. You must follow the recommendations in Section 4. A for strong acids.
D. Formaldehyde (CH
2
0)
Gas loads of formaldehyde making up more than a few percent of the gas pumped can degrade DIRECTORR Gold oil.
There are a number of ways that you can protect your CHEMSTAR pump from formaldehyde. The simplest is to dilute the
gas fl ow (See Section 2 B.) An alternate approach is to use a cold trap (See Section 2 B.)
E. Trifl uoroacetic Acid (F
3
CC0
2
H)
Trifl uoroacetic acid is an extremely corrosive gas. A common application where this acid is employed is freeze drying.
Welch recommends an acid neutralization trap, cat no. 1420H-21 or 1420H-20, (See Section 2 C.) be used whenever this
gas is pumped. If in your application you will be pumping a heavy water load, such as freeze drying, a cold trap should
be used (See Section 2 C. for details and an explanation as to why) between the freeze dryer and the acid neutralization
trap.
CAUTION
When pumping heavy water vapor loads, failure to place a cold trap
between the vacuumchamber and the acid neutralization trap will lead to
rapidly saturated element and resulting in reduced effectiveness of the acid
neutralization trap.
If the acid neutralization trap affects the pumping speed and ultimate pressure adversely in your application, Welch
recommends the use Welch oil fi ltration system, cat. No. 1418G, with an alumina element, cat. No. 1418G-02.
F. Ozone (O
3
)
Ozone is a strong oxidant and very unstable.
WARNING
Ozone is an explosive hazard in its liquid form. Do not attempt to use a cold
trap to condense outthe ozone. Prior to working with ozone, read a handbook
on hazardous materials (for example, Dangerous Properties of Industrial
Materials, Sixth Edition, by N. Irving Sax, Van Nostrand Reinhold Company
Inc. NY, NY 1003, 1984) to determine if any gases you will be pumping
reactdangerously with ozone.