Vacuum Chamber Construction

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Mark Rowley
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Re: Vacuum Chamber Construction

Post by Mark Rowley » Thu Feb 27, 2020 8:40 pm

A+ in my book. Here’s why.
You are not a professional welder but your effort and extreme focus are far beyond 99.99999% of most people here who attempt this type of work on their own. ESPECIALLY at your age! Bravo to the extreme!

In the realm of amateur work (which is what this group is about) you get top scores.

Mark Rowley

Ps...yes, there’s always room for improvement. But that’s true for even the best cut diamond in the history of human existence. Doesn’t mean an A+ isn’t warranted.

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Nicolas Krause
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Re: Vacuum Chamber Construction

Post by Nicolas Krause » Tue Mar 03, 2020 12:18 am

I am now working on the pumping system of the fusor. In addition to the previous vacuum sensor and uC board I've mentioned earlier I also have a surplus vacuum pump and turbopump without controller. I haven't turned on the vacuum pump since I bought it, nor have I monkeyed around with the turbopump. At this point I plan on working on the vacuum sensor circuit, and then building a controller for the turbopump. At that point I can start to troubleshoot the complete vacuum system.
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Rich Feldman
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Re: Vacuum Chamber Construction

Post by Rich Feldman » Tue Mar 03, 2020 12:56 am

Nice looking sock there.

How 'bout starting with vacuum gauge, then characterizing the rotary vane (backing) pump?

Scratch-building a turbo controller would be a learning exercise much bigger than making and welding your chamber parts.
You can go a long way without it.

I would plumb up the chamber, with or without turbo pump, and learn the pumpdown behavior.
Then light a plasma using any old HV power source.
I don't remember whether NST-powered plasmas typically extinguish at pressures attainable with rotary pump (50 micron? 10 micron?)
They sure do in pencil-size glass tubes.
All models are wrong; some models are useful. -- George Box

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Nicolas Krause
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Re: Vacuum Chamber Construction

Post by Nicolas Krause » Tue Mar 03, 2020 1:25 am

Funnily enough I feel a lot more comfortable on the electronics side than the machining and welding side. I've got an electronics technologists diploma, I'm 3/4 of the way through an electrical engineering degree, and I've done some embedded programming for a small oil company up here in Canada. I think like a lot of people I initially joined up here hoping to be the one to crack the fusion puzzle, but reality sets in and instead this project has turned into a tremendous self-education tool. While I think building a motor controller would be tough, it's exactly the kind of thing I'd like to learn how to do.

All that being said, I think I'm going to take your advice Rich and test the backing pump with my vacuum gauge first, then I can move on to the turbopump controller.

I do have a couple options for high voltage supplies, I bought a high voltage transformer a few years back and I've got a busted spellmann supply I picked up off of eBay last year. Finally the quickest route might just be to grab one of those precipitator supplies off the internet.

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Mark Rowley
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Re: Vacuum Chamber Construction

Post by Mark Rowley » Tue Mar 03, 2020 2:21 am

Nicolas, the precip supplies work ok with the 2.75" system but will not put out the current needed for a large spherical arrangement like yours. Theyre cheap enough and it could be worth a try, just dont expect much from them with your arrangement. They may be ok for plasma / vacuum testing as long as you keep a sharp eye on the current draw.

Rich, it's been my experience to have NST driven air plasma extinguish well within the range of a decent roughing pump. Going below 35mTorr things quickly get flickery.

Mark Rowley

Rex Allers
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Re: Vacuum Chamber Construction

Post by Rex Allers » Tue Mar 03, 2020 5:06 am

from Nickolas:
"All that being said, I think I'm going to take your advice Rich and test the backing pump with my vacuum gauge first"

Yes indeed. One step at a time when possible and that is a basic good one. What kind of gauge have you?

If your gauge is good and on the pump input that sets the best you can expect at the pump.

I'd use just that one pump first onto your chamber to see if you can prove there are no big leak problems. If things look good seal the chamber off and see how it holds the max vac you achieved. That should define any minor leak issues.

Last, go on to add the secondary pump (Turbo or diff). At lower levels outgassing issues might look like leaks.

Issues along the way need to be worked on or thought through. You are doing great.
Rex Allers

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Nicolas Krause
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Re: Vacuum Chamber Construction

Post by Nicolas Krause » Tue Mar 03, 2020 6:07 am

Hi Rex,

I have two, a pirani and a thermocouple. I'm going to start with the thermocouple, build a circuit and write a little program to measure the pressure and update a spare LCD I've got lying around. As far as my vacuum pump. there are a couple issues, first it has no electrical chord atm, and second its leaking a decent amount of oil from the black tube out its back. The pump is a leybold trivac D4A, I've managed to find a copy of the manual online, so I'll go through that next.

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Re: Vacuum Chamber Construction

Post by Rex Allers » Tue Mar 03, 2020 7:08 am

Re:
" its leaking a decent amount of oil from the black tube out its back"

That sounds unusual to me. Not sure what to make of the black tube or this leak of oil. Not something I would expect from a normal working pump.

Key, I guess, is what vacuum you get at the input of the mechanical pump. Second, does it have other issues -- like: what's with this oil you mentioned.
Rex Allers

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Richard Hull
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Re: Vacuum Chamber Construction

Post by Richard Hull » Tue Mar 03, 2020 2:15 pm

Is this leak in between the motor and the back of the pump body? If so, you have a shaft oil seal leak.
A year ago I purchased an Edwards speedivac 2 at a yard sale for $5.00. It leaked oil, copiously, at the seal. I finally got around to ordering the oil seal ($32.00 - Duniway). Installed it and cleaned the fairly clean looking guts. It had a decent vacuum to the thumb over the inlet once new oil was in it. After the fix, I had zero oil leak. Unfortunately, it would not indicate on a TC gauge. So, I hooked up to the normally shunned, but telling 0-30-inch gauge and it would pull 26-inches!!! (~40 torr!!). I was hoping for at least 20 microns, (0.02 torr). I now have a perfectly sealed, worthless pump. Oh well....

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.

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Nicolas Krause
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Re: Vacuum Chamber Construction

Post by Nicolas Krause » Fri Mar 06, 2020 2:27 am

After reading parts of the manual and inspecting the pump visually the leak appears to be from one of the oil drain ports. So it may not be a leak after all! A black rubber tube is hooked up to a brass fitting and it is this tube that the oil is draining out of. I'm not sure if anyone can explain the reason for this hookup, in the manual it shows a screw in the drain port. I had to put a new power chord in place, the old one had been chopped off. I'll wait to put the cover for the power chord connection back on until I've ordered a strain relief plug, the current one I have is too small for the chord in question. After making the connections I've plugged it in and the pump turns on and appears to work without too much trouble! I'll have to complete my vacuum gauge circuit next to characterize the pump.
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