System Manual
Oxford Instruments Plasma Technology
OpAL
WARNING
BEFORE PROCEEDING WITH ANY MAINTENANCE WORK, READ SECTION 1 - HEALTH AND SAFETY.
6.8
Pump lubricants
CAUTION
When changing or topping-up the lubricating oil in a pump, always use oil
of the same brand and type. If a change of brand or type is contemplated,
refer to Oxford Instruments Plasma Technology for advice.
6.8.1
General
The lubricating oils used for pumps where the oil comes into contact with the pumped
gases, i.e. oil-sealed pumps such as rotary vane types, should be chosen to meet the
specific characteristics necessary for the process involved.
The vapour pressure must be low at the temperatures reached at the rubbing surfaces.
Viscosity should not vary significantly over the temperature range involved, and the water
absorption rate and content must be low.
Lubricating oils generally fall into one of two categories: mineral (hydrocarbon) based oil
or synthetic oil such as perfluorinated polyether. The synthetic oils are normally used
where they come into contact with strong oxidants such as nitrogen dioxide, oxygen, or
one of the halogens.
6.8.1.1
Perfluorised polyethers
Perfluorised polyether (PFPE) lubricants have the following properties:
a) They are stable up to 350°C, i.e. they do not decompose below this temperature.
b) They are chemically inert. They will, however react with Lewis acids (BCI
3
, AICI
3
etc.) at temperatures over 100°C.
c) They do not polymerise under the impact of high-energy radiation.
d) Since they tend not to keep contaminants suspended, always consider whether
suitable oil filters are needed for the application.
e) They do not 'age' and therefore, if used correctly, need not be replaced during the
lifetime of the pump.
f) Any contaminants in the lubricant may be removed by fitting clean filters and
letting the pump run for several hours with inert gas ballast, the intake port
having been closed.
g) They do not protect metal surfaces against corrosion. Pumps should therefore
always be flushed with inert gas. Pumps using PFPE should be allowed to run
continuously, unless the process is non-corrosive and the pump is vented to dry
Nitrogen.
h) PFPE is incompatible with hydrocarbon oils, i.e. mineral oils, conventional greases
and cleaning agents.
If a pump uses PFPE lubricant only Freon 113 or Frigen 113 may be used as a
cleaning agent, and only PFPE grease may be employed.
Maintenance
Printed: 14-Jul-10, 8:14
Page 6-13 of 16
Issue 4: July 10
Summary of Contents for OpAL
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