Turbo pump - vibration and noise at a certain RPM

[Plat]

I have picked up a used pfeiffer turbomolecular pump and controller for pretty cheap.

It runs like a champ, completely smooth and quiet except for when it’s first starting up.

As it approaches 5500 rpm, it starts vibrating somewhat and sometimes produces a momentary scraping noise when the vibration is worst. This noise then stops and the vibration fades away as it continues speeding up.

The vibration definitely seems to cause the scraping noise. It never occurs at any other time.

The pump looks to be in excellent condition otherwise. It looks pristine inside and the bearings are smooth and not loose or tight.I’m just concerned about the noise and vibration because it doesn’t seem normal. I have never worked with a turbo pump before so learning here.

I don’t understand why, if the vibration was caused by the rotor being off balance, wouldn’t the vibration keep getting worse at higher speeds?

Do you think I should just run it and hope for the best or definitely try rebuilding it?

 

[phinds]

I don’t understand why, if the vibration was caused by the rotor being off balance, wouldn’t the vibration keep getting worse at higher speeds?

could be hitting a resonant frequency of the bearings or something at that particular speed but only that speed.

 

[nsaspook]

A scraping noise is never good. A slight increase in vibration at one or more points is normally because of a mechanical resonance in the rotor, that's normal during a spin-up. I would suspect it was dumped hard a few times, warped a few blades to almost touching (touching slightly during max vibration) and is slightly unbalanced causing stress on the blades at high speed. It might blowup in 30 seconds pumping a large gas load or it might last years with a light load and minimal stress.

If it does fail at full speed the results can be expensive.

A clean destruction.

A dirty one on an Ion Implanter at full beam power.

Every bolt nut sheared off as the turbo lifted from the chamber at e-5 Torr vacuum.

Found a few that hit the top of the enclosure.

The studs are designed to break at X pull. This reduces the possibility of the chamber wall being warped
by a turbo failure.

Ion source and beamline pumps

Turbo parts inside ion source chamber. Ion beam manipulator.

 

[phinds]

View attachment 246153

Ouch !

 

[nsaspook]

Ouch !

It dusted all the product in the machine with graphite combustion/destruction products

The shiny edge on the top wafer is what they all should look like. The once white label on top of the wafer holder is what every inch of the normally clean processing end chamber looked like after the implosion shock-wave traveled inside the machine from the source failure.

His turbo was pretty cheap because the risk of damage is high during a turbo failure.

 

[Tom.G]

Send it back to the manufacturer for evaluation or rebuild. Very likely the lowest-cost approach.