Turbo molecular repair covers two machines: the turbo molecular pump (also written turbomolecular) and the controller that drives it. When a system stops reaching high vacuum, either one can be the cause. Here is how each works, what wears out, and how to tell which one has failed.
How a turbo pump works
Inside the housing, a stack of bladed rotor disks spins between rows of fixed stator blades, at up to 90,000 rpm. The angled blades strike gas molecules and knock them toward the exhaust, stage by stage. This works only when the gas is thin enough that a molecule crosses from blade to blade without hitting another molecule first.
So a turbo pump never works alone. A backing pump, such as a rotary vane pump, takes the exhaust side down to roughly 10⁻² mbar and carries the gas out to atmosphere. Together they reach clean vacuum from 10⁻³ down to 10⁻¹⁰ mbar.
Where you find them
That clean vacuum is why turbo pumps sit on semiconductor etch and ion implant tools, coating systems, and research chambers. They also run inside analytical instruments: mass spectrometers and helium leak detectors both carry one.
What the controller does
A brushless DC motor drives the rotor, and the controller powers the motor. The controller can be a separate box or electronics built onto the pump. The controller also guards the pump. It trips to a fail state when an interlock opens, the pump runs hot, or the pressure climbs too high. It can also open the vent valve as the rotor slows.
Controller faults have their own post: Controller electrical faults.
What wears out
Bearings, first. A common design holds the rotor on a permanent magnetic bearing at the high-vacuum end and an oil-lubricated ball bearing at the exhaust end. In Edwards' EXT pumps the bearings typically last more than 20,000 hours, less on demanding duty, and they are not user-serviceable.
Then the rotor. Dust wears the blades, and enough of it can mean a new rotor. Every start and stop counts too: Edwards gives the EXT rotor a typical life of 40,000 to 50,000 cycles. Venting a pump at full speed with too fast a pressure rise shortens its life, and hard knocks damage the bearings.
More on bearing wear: Turbo pump bearings. For service intervals, see Turbo pump maintenance.
Which one failed?
Edwards' fault-finding table for its EXT pumps is a fair general guide:
- Nothing happens at start, though the power, fuse, interlocks, and cable are fine: if the controller's first speed light never comes on, Edwards points to the controller; if it does, to the pump.
- The rotor will not turn freely: suspect the bearings.
- The pump is noisy or vibrates: first rule out resonance with the system and vibration carried up from the backing pump. Irregular noise that keeps getting worse points to a bearing; a constant high-pitched one, to a rotor out of balance.
The full checks, from power to cooling, are in Troubleshooting turbo pumps.