38 R&DMagazine June 2014 www.rdmag.com
The launch of a new vacuum pump line from Oerlikon Leybold marks the arrival of a
long-awaited development in turbomolecular pump design.
The concept for a turbomolecular vac- uum pump is based on a very basic principle: mechanical motion can be transferred directly to gas molecules to
create a vacuum. This idea, which was first
implemented by molecular drag pumps in
the 1930s and 1940s and later refined in the
first turbomolecular pump in 1958, has been
so effective that few other solutions exist to
provide this high level of vacuum performance in such a compact space.
Designed so that rotors with angled fins
spin in a single direction, turbomolecular
(or turbo) pumps push air from one “stage”
to another, compressing flow air. To do this
effectively, the pump must operate at high
speeds, building up friction heat that has
always dictated how reliably a pump can run.
Modern ceramic ball bearings are extremely tough, but must be cooled by oil that eventually must be changed in order to prolong
the life of the expensive bearing. This oil, a
low vapor-pressure grease, can also introduce
contamination, especially on the low-pressure side of the pump. Magnetic bearings
have been the preferred solutions to eliminate use of oil, but they are consistently
more expensive to manufacture.
At Pittcon 2014, Oerlikon Leybold
Vacuum, Pittsburgh, Pa., introduced its
first turbomolecular pump that combines
both magnetic and traditional mechanical
The “hybrid” approach used in the new
Turbovac i was employed to not only reduce
the use of oil in its pump, but eliminate it
completely, potentially bringing oil-free
turbo pump operation to a wider set of customers.
Since 2009, says Dieter Mueller, global sales
support manager at Oerlikon Leybold Vacu-
um, the company started basic development
on a new vacuum pump. Engineers evaluated
the overall performance of every component
of the system, starting from the basics. They
were equipped with a set of performance
goals that would help guide the development
over the next five years. One of the biggest
goals was to offer a substantial improvement
in reliability. The design specification called
for a pump that would last four to five years
“But we also wanted to double quality.
We wanted to improve mean time between
failure (MPBS),” says Mueller. “Our goal was
to develop a pump that would be relevant
through the year 2020 and beyond.”
Another goal was to deliver a pump that
would provide higher sensitivity and better
analysis capability when used for research.
The developers also sought higher pump
But specifications alone didn’t guide the
development process. One of the major
aspects analyzed was Oerlikon Leybold’s
manufacturing capabilities. Substantial met-
allurgical analyses conducted during pump
development helped inform the company
about changes that could be made during
the manufacturing process to improve pump
reliability and improve responsiveness to the
needs of their customers.
“In order to fulfill the needs for some of
our OEM customers, such as makers of mass
spectrometers, we have to produce pumps
quickly, three months or faster,” says Mueller.
Hybrid bearing eliminates oil change
Oerlikon Leybold offers several types of turbomolecular pumps and they vary mainly
in the type of rotor suspension that is used.
In the past, the line-up was split between the
Turbovac, which features mechanical rotor
suspension, and the Turbovac MAG, which
features a magnetic suspension for the rotor.
Each is equipped with a classic turbomolecular pump with the option of a compound
stage for use with backing pumps.
The new Turbovac i cleaves to the same
classic formula, but differs in bearing design.
Called a “hybrid”, the new bearing combines
the features of a mechanical and magnetic
bearing design system, with a ball bearing on
the fore-vacuum side and a magnetic bearing on the high-vacuum side. The magnetic
bearing is passive and uses repulsive forces
between permanent magnets to control the
rotor position. This allows that bearing to be
non-contact and free of oil. The ball bearing,
meanwhile, is designed to be easily accessible for servicing and oil changes. This type
of bearing design has been implemented
in the recent past by other turbomolecular
pump manufacturers, notably Pfeiffer and
Edwards Vacuum. In the case of Pfeiffer’s
hybrid pump, which has been on the market
for a number of years, the bearing can be
serviced in the field in just 30 min. As little
as 10 years ago, most turbomolecular pumps
required shipment to the factory for refur-bishment and oil changes. In the last five
years, Edwards Vacuum also shifted to hybrid
bearings for its EXT line of pumps.
Five years of development preceeded the
launch of Oerlikon Leybold Vacuum’s most
advanced turbomolecular vacuum pump, the