Can a house hold copper pipe hold a vacuum?

Every fusor and fusion system seems to need a vacuum. This area is for detailed discussion of vacuum systems, materials, gauging, etc. related to fusor or fusion research.
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Andynerd
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Can a house hold copper pipe hold a vacuum?

Post by Andynerd »

I was wondering if a 2"-4" copper pipe can hold any sort of vacuum. I was going to assume since they can contain a fluid much greater then atmospheric pressure that they should be able to withstand the atmospheres pressure. Then again that is using the pipe for a completely opposite purpose then it was designed for. If there was a calculation to find out what kind of vacuum it could hold that would be great.
richnormand
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Re: Can a house hold copper pipe hold a vacuum?

Post by richnormand »

I have done it several times with 1" and 1.5” pipes up to 2 feet. Biggest issue was to get them clean for good vacuum.

My guess would be that 2" and bigger is good too, but you should look at the wall thickness closely. It might by OK for short lengths, then you might need regular braces to prevent buckles on long lengths, all depends on the wall thickness.

Have a look at :

http://www.copper.org/applications/plum ... 4apps.html

under 4.12 on medical vacuum piping.
Conrad Farnsworth
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Re: Can a house hold copper pipe hold a vacuum?

Post by Conrad Farnsworth »

I believe the FAQ's outline this somewhat. As far as metal thickness goes. Its all here but its like a needle in a haystack
Andynerd
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Re: Can a house hold copper pipe hold a vacuum?

Post by Andynerd »

Sorry I didn't see that in the FAQ must have missed it... Anyway I was just planning on using a 2" copper fitting (the kind that's a T shape the name escapes me). Since it has thick walls especialy around the middle. I was going to use it to be my chamber for a very small demo fusor. I saw it done with 2" borosillicate tubing but I don't live anywhere near a place to get some. So I thought copper pipe might be a close second. Only issue is figuring out a viewport...

I guess I could always try using a testube instead but I don't know how much vacuum a testube would handle.
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Rich Feldman
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Re: Can a house hold copper pipe hold a vacuum?

Post by Rich Feldman »

Strength will not be a problem at 2" size. I expect not at 4" size and any standard "pipe" thickness; can't point to a reference but Google should be able to do the job.

The plant where I work has vacuum (for mechanical equipment) distributed with 2" copper pipe. The main joints use solderless couplings and tees with internal gaskets, crimped onto the pipes with a hydraulic tool. For one-off use, I might try drilling holes for set screws.

When that system went in, a co-worker told me of his experience at a plant with many high-vacuum pumps. Roughing vacuum was distributed in copper pipe from a central station. Apparently they were troubled by leakage flow from porous plumbing (? !), and mitigating it by painting the outside with epoxy. (?)

It's hard to imagine a test tube, or even a glass cigar tube, not strong enough to safely be evacuated. As with all glass vessels, the concern is local heating when your demo plasma is going.
All models are wrong; some models are useful. -- George Box
Andynerd
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Re: Can a house hold copper pipe hold a vacuum?

Post by Andynerd »

I agree with the test tube thing. Since most test tubes or lab equipment is made from borosilicate glass I wouldn't expect a small run with the demo plasma to cause much problem. All I need is a few minutes running the demo plasma to test my experiment.
I assume the leak rate on typical plumbing valves shouldn't be to bad.
Starfire
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Re: Can a house hold copper pipe hold a vacuum?

Post by Starfire »

The maximum pressure differiental from a vacuum is one atmosphere - very large dia pipes of very thin wall may be a problem but standard domestic pipe must meet standards which require withstanding several atmosphere test pressure.
tligon
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Re: Can a house hold copper pipe hold a vacuum?

Post by tligon »

Sure it will!

Pulling a vacuum on copper is the best possible test of your "sweating" skills. Any tiny leak in the solder will show you your lack of skill. I have not tried lead-free solder with a vacuum yet, but silver soldering is used in vacuum work and ought to be slightly better than lead/tin.

We used to make vacuum UV sensors using copper chambers with special windows, at a lab where I used to work. We placed the parts, unsoldered, in a high vacuum system, and applied steps of inductive heating to the parts. At fairly low heat the copper cleaned itself, going very bright and shiny. Then we backfilled the system with a little halogen gas (the UV detector) and jacked the inductive heating up to melt a ring of silver solder that sealed the window in place.

The resulting sensor was good for some years. The clean copper surface inside probably acted as a "getter".
David Geer
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Re: Can a house hold copper pipe hold a vacuum?

Post by David Geer »

Gotta agree with Tom. Silver/lead alloy solder is best for copper or tin metals. I've worked in building pipe organs in a family business and harmonics also requires perfect seals and we used the silver/lead bar stock solder with a soldering "hatchet". Has a decent melting point and very easy to work with. Strong solder connections even up to 40-50lb 20' piping.
- David Geer
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