Death of a turbo

Chad Orzel at Uncertain Principles currently has a nice post up on vacuum pumps – equipment that’s pretty much essential for anyone doing any kind of nanofabrication or materials characterisation work. Coincidentally, someone in the lab hauled out a turbopump today so we had an opportunity to take some photos.

Though, of course, you really, really never want to see turbopumps in this state.

Here’s a view through the top connecting flange of the turbo. Normally, you should see quite nice, regular, closely-spaced blades arranged around a central shaft, much like the turbines of a jet engine. Obviously that’s not quite the case here – this is a turbopump that’s just gone through a rather catastrophic failure, possibly arising because of some small object, a wafer fragment say, dropping right into it. There’s usually a safety mesh placed over the turbo opening to prevent such occurrences from happening, but sometimes holes get ripped in it.

A large turbopump like this usually has its turbines spinning around 3000 rpm or so – about 50 times per second. That’s pretty darned fast, and when something gets in the way of something with this much angular momentum, well, bad things happen. Like turbine blades jamming and then shearing off:

A turbopump typically contains a series of rotors; each one compressing and driving gas towards the outlet leading to a backing pump. Here, about two or three levels down, the rotor itself has been thrown off axis:

Did I mention that these guys can cost SGD$100,000 or more?