First turbo pumpdown - smooth sailing!

[ChristofferBraestrup]

I'm excited beyond words!

After owning a -presumed working- turbo for a year, and having bought parts here and there since then, today my ISO100 viewport and clamps came, and I was finally able to test it.

After an hour at rough vacuum, it had stabilized at around 0.1 mtorr, and I dared switching on the turbo. It spun up beautifully, no vibrations to speak of. It reached "TMP OK" - meaning 80% full speed in a matter of minutes, and a steadily climbing speed into the 80's %.

My actual ISO100 chamber hasn't arrived yet, and I have yet to make a controller for my active inverted magnetron gauge, so the ultimate pressure to be achieved remains to be seen.

Shutdown went smooth also, I'd say this was a successful first test!

The setup:

Homebrew PSU/controller for the EXDC160 TMP driver:

The pirani gauge controller (Edwards APG-m-nw16):

[Richard Hull]

I assume you blanked the turbo off with what appears to be a large view port glass?? The Photo is puzzling.

Richard Hull

[ChristofferBraestrup]

Yes, exactly right! From the image it just looks like turbo pump murder. There is a huge viewport clamped over the pump flange.

I'm not sure what material the window is made from, if its quartz I feel like I got a bargain, but more likely borosilicate glass.

[Richard Hull]

Whew! I am glad for both of us. I guessed right and you still have a working pump. Actually, beyond the possibility of an open throated pump sucking in something damaging, the pump would not spin up dangerously on most systems if left uncovered due to high pressure drag forces, sort of self limiting. There is nothing wrong with open throat quick testing to the level of just making sure the pump and controller will spin as a working unit for just a few seconds of runup and then power down.

Richard Hull

[ChristofferBraestrup]

Right. I was relieved the bearing seemed good, since that's hard to tell at a low RPM fast on/off.

I hadn't thought about the open turbo thing, that makes sense. I guess the catastrophic failure mode is rapid venting while the pump is at max (60.000rpm) speed.

Even if the viewport cracked i dont think the recompression would be rapid enough to do in the pump.

The whole setup gets quite toasty, after an hour I would estimate 60°C. I should really add a fan to the turbo, although on many a mass spectrometer, the TMPs routinely run without forced air or water, and just coast at 50-60 C.

[John Futter]

Christoffer
I'm puzzled by the high turbo temp 60 degrees is high considering assumed no load ie blanked off.
when a turbo that hasn't been used for some time is started you are supposed to ramp it up part way through its range and stop doing it again and again creeping higher in rpms.
This is to reallocate the bearing lubrication evenly.

hopefully your next try will result in lower temp as you have done the first cycle albeit a bit higher than recommended

[Dennis P Brown]

Most ceretainly add a good fan; while 60 C is an acceptable 'bake out' temp for a turbo its is too high for typical operation. A fan will also extend the useful life of the turbo.

Waiting to reach 0.1 milli-torr to turn on the turbo isn't necessary. I routinely start mine anywhere from 50 to 100 milli-torr and that takes just a few minutes (and that is on a large chamber system taht had been previously been open to air, not a no-load, small system.) However, most mechanical pumps will struggle to get below a few microns (or a few milli-torr.) Either your mechanical pump is extremely good or your calibration might be off.

Also, a very proffessional rack mounting system you created for the turbo controller & vacuum gauge.

[ChristofferBraestrup]

Thanks for the replies!

I will install a fan for continued use at some point. My forline pump is pretty excellent, an almost brand new 2-stage Cole-Parmer pump, with just a gauge fitted on it, I can get slightly below 10^-2 torr. The initial vacuum was to set all the clamps, as they need re-tightening after pumpdown, and make sure the viewport didn't crack, and was vacuum tight.

The temperature is not that uncharacteristic, in my experience. On a differentially pumped 3-turbo MS, the time-of-flight tube pump (very little load) is running un-cooled at a similar temperature. There's no reason to tempt fate, though, I will add some decent cooling.

My fore-line looks a bit Rube Goldberg-esque, the hose coming up from the roughing pump is so stiff this was the only way It would work. I will improve that at some point.

[Richard Hull]

John is right with his concern. I run a Pfeiffer TCP050 and after one hour the motor base is barely warm to the touch. What is the capacity of your pump? Mine is 50l/s and never gets much above ambient.
Since you have no way of measuring you seal on the window, perhaps it is not all that good and a leaky load is being placed on the pump not allowing it to sync to design speed. Just a thought.

Richard Hull

[ChristofferBraestrup]

I will look into possible leaks. The trouble with the ISO-100 system is that there's no "good" indication of how tight the clamps should be. 5 Nm is often cited, but who has time for torque wrenches right?

Alternatively, the small metal profile of the viewport might provide more flex than a large, rigid pipe section or pump body. Maybe the window in particular could benefit from more clamps around the edge.