A turbo molecular pump's rotor can turn at up to 90,000 rpm, carried by its bearings. The bearing design decides most of the pump's maintenance: what it needs, how often, and what wears it out early. There are three designs, and the pump's manual tells you which one you have.
Ball, hybrid or magnetic
Ball bearings. Two lubricated ball bearings carry the rotor, both on the fore-vacuum side, where the lubricant stays out of the high vacuum. Leybold's TURBOVAC 35 to 1000 C pumps, for example, run on grease-lubricated bearings.
Hybrid bearings. A ceramic ball bearing on the fore-vacuum side, fed by an operating fluid reservoir, works with a permanent magnetic bearing on the high-vacuum side that holds the rotor without contact. Pfeiffer's hybrid HiPace pumps are built this way.
Magnetic bearings (maglev). Electromagnets and distance sensors hold the rotor in suspension on five axes, with no lubricant at all. In a power failure, the spinning rotor powers its own bearings while it slows. If the outage lasts, an integrated safety bearing takes over at very low speed and brings it safely to a stop.
Service intervals by maker
Intervals differ by maker and model, so follow your pump's manual. Some published examples:
- Leybold's grease-lubricated TURBOVAC 35 to 1000 C: a bearing exchange no later than 10,000 to 15,000 operating hours, depending on size.
- Leybold ceramic-bearing turbopumps: a ceramic bearing exchange every 2 years.
- Pfeiffer hybrid-bearing turbopumps: new operating fluid and new bearings every 4 years, or a full overhaul in a service center every 4 to 5 years. The HiPace 60 P manual says at least once every 4 years.
- Maglev: Leybold rates the TURBOVAC MAG for up to 80,000 hours or 10,000 cycles without maintenance, and Edwards calls its STP maglev pumps zero maintenance.
Harsh duty shortens all of these. Pfeiffer asks owners to ask its service team about shorter intervals for extreme loads or impure processes.
Every maker's schedule, side by side: Turbo Molecular Pump Maintenance.
A spare on the shelf ages too
Lubricant ages even when the pump is off. Pfeiffer warns that aged operating fluid can make the ball bearing fail, and calls for fresh fluid after at most 2 years out of use. Before fitting a stored spare, find out when its lubricant was last changed.
What shortens bearing life
- Venting too fast. Leybold: "The slower the pump is vented, the longer the service life of the bearings will be."
- Knocks while running. Leybold says to avoid sharp shocks and sudden changes in position while the pump runs.
- Outside vibration. Pfeiffer warns that strong vibration, earthquakes included, can push the rotor into its safety bearings.
- Particles and aggressive gases. On pumps with purge gas, Leybold says to vent through the purge gas valve, so particles, dust and aggressive gases are not forced through the bearings.
Signs of a failing bearing
The makers' troubleshooting tables point to the bearings, among other causes, when a pump:
- makes unusual or loud running noise, or vibrates;
- overheats;
- fails to reach its rated speed or its ultimate pressure.
Act on the noise early: in Leybold's table, a defective bearing means new bearings, and a seized pump means a new pump.