TECHNICAL INFORMATION
32
87-900-867-01(A)
The recommended gas flow maintains a pressure
into the pump body higher than the forevacuum
pressure.
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.
1. Purge gas line
2. Pressure
regulator
3. Gas purge valve
4. Gas purge port
5. Forevacuum
pump
6. Turbopump
7. Vent
valve
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.
The recommended procedure to vent the system
and the pump avoiding the contact between the
pump bearings and the corrosive gas is described
in the following points:
However if the effect is grater, than the case
should be carefully reviewed by Varian's specialist.
As a matter of fact, in case of high magnetic fields,
also important forces might be generated and ap-
plied to the rotor.
1. Close the corrosive gas flow into the system.
2. Leaving the Turbo-V pump and the backing
pump running and the purge gas flowing, wait
for enough time to evacuate the corrosive gas
from the system.
ACCESSORIES
DESCRIPTION PART
NUMBER
Inlet screen, ISO 250
969-9306
Heater band, 120 V
969-9812
Heater band, 220 V
969-9811
Vent valve with fixed delay
time
969-9833
Vent device with adjustable
delay time
969-9831
Forepump SD 700, with 3
ph., 220/380 V, 50 Hz motor
949-0860-080
Forepump SD 700 with 1
ph., 120/220 V, 60 Hz motor
0424-P1241-307
Forepump SD 700, with 3
ph.,
universal motor
0424-P1241-337
3. Open the Turbo-V vent port slowly until to
reach atmospheric pressure in the system.
4. Turn off the Turbopump.
5. When the Turbo-V pump and the backing
pump are stopped and the system is at at-
mospheric pressure, for a better bearing pro-
tection it is advisable to leave the purge gas
flowing into the Turbo-V pump, with the
chamber or the Turbo-V vent valve opened, to
avoid system overpressures.
If the vent valve can't be kept opened, the
backing pump should be left operating.
For a complete overview of Varian's extensive
product lines, please refer to the Varian catalog.
