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PUMP USED IN PRESENCE OF MAGNETIC
FIELDS
Magnetic fields induce eddy currents in the rotor of
a turbomolecular pump that tend to oppose to its
rotation.
The result is increased electrical power consump-
tion by the motor, most of which is dissipated in
the rotor.
Since the rotor is not in contact with the stator the
above power can leave the rotor mainly by radia-
tion and hence the rotor may be overheated while
static parts of the pump remain cool.
This effect is strongly dependant from the inten-
sity, time function and distribution of the magnetic
field.
In general, therefore, an increase in pump current
can be expected.
If this increase is lower than 50% of the current
value drawn by the motor in high vacuum opera-
tion, no particular problem should be expected.
However if the effect is grater, than the case
should be carefully reviewed by Varian's special-
ist. As a matter of fact, in case of high magnetic
fields, also important forces might be generated
and applied to the rotor.
PREVENTIVE MAINTENANCE
The oil must be changed every six months or
whenever the oil becomes opaque or dark brown.
Change the oil according to the following proce-
dure:
1. Unscrew the screws attaching the oil sump to
the pump.
2. Lower the sump, empty old oil charge.
3. Clean the sump thoroughly (do not use alcohol)
and fill it with a new charge of oil.
4. Reattach the sump immediately to avoid par-
ticulate contamination, making sure the O-ring
is cleaned and properly seated. Do not over-
tighten the screws to avoid breakage of the
sump.
Do not mix oil; use only Varian T.A. oil.
ACCESSORIES
DESCRIPTION
Inlet screen
Vent valve with fixed delay time
Vent device with adjustable delay
time
Varian T.A. oil, 100 cm
Varian T.A. oil, 1000 cm
Forepump SD 1400 with 3 ph., uni-
versal motor
For a complete overview of Varian's extensive
product lines, please refer to the Varian catalog.
32
TECHNICAL INFORMATION
NOTE
PART NUMBER
969-9308
969-9833
969-9831
3
969-9901
3
969-9902
P1261-337
87-900-838-01(B)
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