Specifications

Turbo
Pumps
Turbo-V Pumps
193
Varian, Inc. Vacuum Technologies
In general, the vibrations caused by an electric motor or
bearing are even lower than those caused by unbalance.
They may be relevant in the case of bearing damage or
because of excitation of a natural resonant frequency of the
system connected to the pump. In the second case,
the system structure should be modified by adding mass,
changing the stiffness and/or inserting a vibration damper
between pump and system.
Operation in Presence of Magnetic Fields
Magnetic fields induce eddy currents in the turbomolecular
pump rotor that tend to oppose its rotation. As a consequence
the power delivered to the electrical motor is increased.
Since the pump rotor is not in contact with the stator, all the
heat generated by the eddy currents must be dissipated by
radiation, so the rotor can be overheated even if the static
parts remain cool.
According to our tests, the maximum magnetic field that our
pumps can tolerate is:
• 50 Gauss in the transversal direction
• 100 Gauss in the axial direction
In these cases, a power increase to the motor can be
expected.
If the magnetic field is greater than the above values a shield
must be used in order to have a residual magnetic field
around the pump below the value specified.
Please contact Varian for more details.
Electrical Interfacing
The input/output of our controllers have been designed to
give maximum flexibility to operate the pump remotely.
Two types of interface are offered for the following two
controller families:
• Rack controllers (including V 81, V 301, V 550, V 700HT,
V 1000HT)
• Navigator controllers (including V 301, V 551, V 701,
V 1001)
Please contact Varian for more details.
Turbomolecular Pump Bearings
and Lubrication System
The Turbo-V pumps incorporate Varian’s innovative ceramic
bearing design with a proprietary ultra-low vapor pressure
solid lubricant, which enables these pumps to provide a long
service life and a high degree of cleanliness under most
operating conditions. This lubrication system is a superior
feature of Varian Technology and guarantees no contamination
of the vacuum system, especially when compared to other
oil-lubricated turbomolecular pumps (See figures 5-6).
The ceramic bearings utilize balls made of silicon nitride, a
polycrystalline material with an amorphous intergranular
binder base that offers the following advantages:
Hardness
This is a critical aspect of bearing design, and it closely
relates to bearing performance and reliability. The silicon nitride
material used in Varian’s Turbo-V bearing system is twice as hard
as conventional steel providing dramatic improvement
in wear resistance while minimizing the effects of surface
contact and stress.
Weight
Silicon nitride is 40% less dense than conventional steels, which
helps to reduce centrifugal loading and stress levels at high
rotational speeds, especially in the bearing race area.
Friction
Silicon nitride’s low coefficient of friction enhances wear
resistance and adds to the bearing’s operational life.
Thermal Stability
With its low thermal expansion coefficient, the silicon nitride
bearing material ensures that tight tolerances and mating
component fit will be maintained over an extremely wide
temperature range. In addition, silicon nitride has an
outstanding resistance to fracture by thermal shock.
Chemical Stability
Silicon nitride is virtually inert.
1
611
H
2
10
-9
10
-10
10
-11
10
-12
16
H
2
O
21 26 31 36 41 46 51 56 61 66 71 76 81 86
a.m.u.
N
2
O
2
CO
2
P (Torr)
1
611
H
2
10
-8
10
-9
10
-10
10
-11
10
-12
16
H
2
O
21 26 31 36 41 46 51 56 61 66 71 76 81 86
a.m.u.
N
2
O
2
CO
2
CF
2
C
3
F
CF
3
C
5
F
P (Torr)
Typical Competitor Pump
Typical Varian Pump
Figure 5
Figure 6