First turbo pumpdown - smooth sailing!

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Jim Kovalchick
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Re: First turbo pumpdown - smooth sailing!

Post by Jim Kovalchick » Thu Nov 19, 2020 7:40 pm

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.

ChristofferBraestrup
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Re: First turbo pumpdown - smooth sailing!

Post by ChristofferBraestrup » Thu Nov 19, 2020 8:30 pm

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.

Albert Mery
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Re: First turbo pumpdown - smooth sailing!

Post by Albert Mery » Thu Nov 19, 2020 9:06 pm

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?

ChristofferBraestrup
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Re: First turbo pumpdown - smooth sailing!

Post by ChristofferBraestrup » Thu Nov 19, 2020 9:12 pm

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.

Albert Mery
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Re: First turbo pumpdown - smooth sailing!

Post by Albert Mery » Thu Nov 19, 2020 9:22 pm

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.

ChristofferBraestrup
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Re: First turbo pumpdown - smooth sailing!

Post by ChristofferBraestrup » Thu Nov 19, 2020 10:31 pm

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.

ChristofferBraestrup
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Re: First turbo pumpdown - smooth sailing!

Post by ChristofferBraestrup » Thu Nov 19, 2020 11:22 pm

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.
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Richard Hull
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Re: First turbo pumpdown - smooth sailing!

Post by Richard Hull » Fri Nov 20, 2020 5:10 am

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

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

ChristofferBraestrup
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Re: First turbo pumpdown - smooth sailing!

Post by ChristofferBraestrup » Fri Nov 20, 2020 8:09 pm

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.

ChristofferBraestrup
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Re: First turbo pumpdown - smooth sailing!

Post by ChristofferBraestrup » Mon Nov 23, 2020 8:19 pm

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.
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