Chamber construction

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fpg
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Chamber construction

Post by fpg » Sun May 23, 2010 10:19 pm

I found a company that has agreed on constructing a vacuum chamber for my project. They said that I should send them some schematics on the chamber. The problem is that I do not have any experience at all on how to make schematics. I would be pleased if I could get some general advices on how to make such schematics.

I have 3 plans on my chamber design as shown in the first picture below.
Nr.1 is the classical spherical vacuum chamber.
Nr.2 is a sort of large crossed fitting (don’t now what it’s called).
Nr.3 is a cylindrical vacuum chamber (also shown in picture 2).
Which of the chambers mentioned do you think is the best alternative for a poor student?

The second picture is my basic schematic of my fusor. I wonder if it’s anything that I’m missing and if there is anything that should be changed?

The company also recommended a Santovac 5 diffusion pump fluid 100ml for 380 dollar !?
Is this a reasonable price for diffusion pump oil or is there any cheaper alternative ?

Thanks in advance

Regards Fredrik PG
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Tyler Christensen
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Re: Chamber construction

Post by Tyler Christensen » Sun May 23, 2010 10:38 pm

There are merits to every chamber geometry, you need to decide what you personally want. I like spherical chambers, I know other people have had great luck with cylinders. Generally the tee/cross option is the "budget" option because they frequently come up on ebay for low prices all pre-built. I wouldn't recommend having a tee/cross custom built, but I suppose it would be an option.

As far as schematics, here is a bit of information on how to draw the schematics: http://www.mdcvacuum.com/searchs/doc/Ch ... ometry.htm

I imagine other sites have even more information on it.

Regarding the diffusion oil, no there is no point in spending that much. You can get DC704 on ebay much cheaper ($29.50 for 50mL), that's my preferred oil. There are other oils that are even cheaper, but quality does matter.

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Doug Coulter
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Re: Chamber construction

Post by Doug Coulter » Mon May 24, 2010 1:17 am

I'm the cylinder guy here, but you know what? Tyler is correct in every regard.

The reason for that real expensive stuff doesn't obtain in most all fusors. Santovac shines in things that use very, very, low currents and often also low fields, which is mostly not relevant here.

In some conditions (think electron microscopes or some kinds of mass spectrometers) oil can build up and make an insulator of parts of low-field E lenses, which really messes up some electron microscope or surface measurement technologies -- which is why they've all moved to oil free systems entirely these days.

In a fusor, a bit of oil contamination merely is burned right off, and down the pumps it goes. I run both diff pump and oil free systems here, and there's just nothing significantly different enough to write home about, and I don't even use the DC 704 stuff, I use the even cheaper Diffoil-20 and only have a cool water top/trap on it, no problems with it. We may upgrade that system to vacuum pumps from a leak detector that run the good stuff, but that's because we have it, it's free, and the pumps are more "right sized" than the overkill ones we have on that system now, which is an important consideration here, running on solar PV power. A 6" tee doesn't exactly need the 4" diff pump and 1 hp backing pump that's on there now, is all, and it would be nice to save some kilowatts on that system.

So you don't need the really good stuff unless you're going fairly well outside the normal fusor realm, or are just a perfectionist. If you are the latter (and well off), think "turbo-drag" and "oil free" or "cryogenics".

The turbos are more convenient to run, but I can't say they really produce much better results.
We get pretty consistent results across the pump types here, for what it's worth.
Why guess when you can know? Measure!

Jerry Biehler
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Re: Chamber construction

Post by Jerry Biehler » Mon May 24, 2010 10:28 am

Are you planning on be able to open the chamber while the diff pump is up to temp? If so then you will need a valve between the diff and the chamber. This will also help throttle the pumping speed of the diff pump. If not then you can eliminate the roughing line to the chamber. It is not necessary.

DC704 or 705 is all you will need. They just want your money. I am using some stuff called Vacoil-S. Its similar to 705.

You could also top Doug's turbos and cryos with ion pumps.

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Doug Coulter
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Re: Chamber construction

Post by Doug Coulter » Mon May 24, 2010 3:47 pm

Yes, you could top them easy. I built a Ti sublimation pump kinda by accident trying to evap the stuff for deposition on something, and it works really well. I don't use that as it's just not needed for what I'm doing, and with any Viton at all in the high vacuum side, would need to run all the time.
I've not tried making an ion pump yet -- considerations of stray mag field are important to what I am doing right now. I'm sure it would work great.

I personally avoid cryo due to the running expenses -- I live a long way from anywhere you can get the cool stuff anyhow.

For me, the turbos hammer the systems down to e-7 mbar right quick, and that's plenty good enough. I get to e-6 in under 10 minutes, and with heating, see the e-7 in well under an hour. A little slower with the small turbo and more viton, but no biggie. If I am going from running to open and right back to running, it seems the system doesn't need to outgass that much -- I didn't have the door open long, and I get right back down to operation in a very short cycle time. If I'm in a real hurry, I vent with argon and that really speeds up the subsequent pumpdown, as it's not sticking to things like shop air does.

The main deal with the turbos is that they spin up and back down quick, so you don't have to have a good valve between them and the tank, and can try more stuff per day of work....for just running, the diff pumps are fine, just slower and take more caution to not get air into them when they are still hot.
Why guess when you can know? Measure!

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fpg
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Re: Chamber construction

Post by fpg » Mon May 24, 2010 9:27 pm

It will save me some cost if I can remove the roughing line and have the diff pump in series with the roughing pump instead.

I prefer the spherical chamber the most but it is the price that matters the most. I have max 600 dollar to spend on the chamber construction. I have seen several spherical chambers on the forum and I wonder if it would be possible to get my hands on some finished schematics? I don’t have any program such as CAD or anything like that and I’m afraid that the company would laugh at my hand written drawings .

Glad to hear that the price of diffusion pump oil wasn’t as high as I thought.

chad ramey
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Re: Chamber construction

Post by chad ramey » Tue May 25, 2010 3:15 am

Although not the best, Google's Sketch-up is an absolutely free design software. I'm also pretty sure that Solid Works has a free 30-day trial.

I myself have a tiny (2.75" conflat) 5-way cross that has been nice to get started with but, I'd definitely hop on board with all the sphere and cylinder guys. If you're opting for a sphere, you can acquire the hemispheres for a pretty nice price from sharpe products(some on this forum have actually used stainless steel salad bowls) . The main expense with a sphere would most likely be the flanges but some good ebay-ing skills can get those without breaking the bank.

I'll also back up Doug's recommendation of Lesker's DiffOil-20, I use it and have been very pleased.

Goodluck!
-Chad

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