Fusor Forums

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):

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

Richard Hull

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.

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

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.

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

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.

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.

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

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.

Your picture shows 0.1 torr not 0.1 mtorr. If that's the pressure you are getting with a turbo, that explains the temperature issue.

0.1 torr is my foreline vacuum, the gauge is visible in the first image.

There is no high vacuum gauge yet, as the high vacuum side is just blanked off with a viewport.

Hello, I'm glad to see that your pump is working! I also have an untested pump, an Edwards EXT250, lying around and I have to admit that it's pretty nerve racking. What is the model of your pump?

Good luck with your pump! Yea the first pump down and shutdown is pretty tense! My pump is almost the same as yours, it is the Edwards EXT255H. Driven by an exdc160 controller.

oh, I had no idea these EXDC controllers existed. I had to order a big bulky EXC 300. I had thought about making my own driver and from my meagre knowledge i believe my pump's motor is just brushless motor with some hall effect sensors. Sadly my fear of blowing something up got the better of me.

That's the problem. it's a 3 phase AC motor. The controller is a full-on inverter/VFD!

I found a quirk, by the way. I fed the EXDC160 72VDC in, and the pump wouldn't spin faster than 80% ish - this bummed me out yesterday.

Today I turned my SMPS up to the nominal 80V - and by magic, the speed output instantly showed 100% ! No change in turbo sound pitch, and very fast. I assume the speed out scale (0-10V = 0-100%) doesn't work brilliantly when the controller is undervolted. Either way problem solved.

Spin-up time to 10% is now fairly rapid, I'm going to monitor the temperature over an hour or so to ballpark how much load is on.

Whatever did the trick; more clamps, cleaning surfaces, buffing the PSU (a good scientist always covers his tracks by changing multiple variables at the same time)
now the pump coasts at 28-30 degrees C after an hour of run-time, and at 100% speed.

I call success for now! I'm pleased with the results.

Speaking of limits, I'm a bit annoyed the EXDC80/160 doesn't furnish an analog temp out, as I know the pump has a temperature sensor, the EXDC does detect overtemp.

I consider 6 clamps a minimum on a 4.5-inch system ISO port.

Richard Hull

I have read specifications that sais 8 clamps as well.

And then seen commercial, high volume produced instruments running 4 clamps. I think it has a lot to do with what is clamped. on an instrument with a machined thick-walled vacuum chamber where the pump is mounted to the body, the rigidity is likely great enough that only 4 is needed.

really, the larger the flange, the fewer clamps should be needed, as the force on the joint increases with area under vacuum. approx 1 kg/cm^2, or 78 kg on a ISO100 blind. 490 kg on a ISO250!

Obviously, if the joint is under any load (like a radial turbo sticking out, or holding a heavy vacuum system, one would use all the clamps there's room for for mechanical stability.

Chamber arrived today!

A bent ISO100 piece with 2 KF25 ports.

After 30 mins, a pressure better than 10^-6 torr was reached (I got my inverted magnetron gauge going - first try!)

I'm very happy with this outcome. Temperature is still coasting in the high 20's *c with no active cooling.

I've made a small video about my vacuum system and discuss some design considerations.

Hope you enjoy!

https://www.youtube.com/watch?v=ubcKrm9fWzQ

Nice vid; should post some pics to archive here.

Thanks! I'll try and take some better ones, but most of it is on the previous pages here.

Took some better pictures of the so far 'final' setup.

Hope you enjoy!

It should be a short trip to fusion from here. Great work!

Richard Hull