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Flexible Deuterium Gas Input Hose?

Posted: Sun Dec 16, 2018 1:01 pm
by ian_krase
I'm curious if anybody has any advice on a flexible hose setup for introducing gas into their vacuum system. Normally one uses fixed metal tubing between the metering valve and the fusor -- which works well for most fusors but is inconvenient (even if bend-by-hand refrigeration tube is used) for vacuum systems that get reconfigured.

I know that thin metal bellows tubing exists, but it is dear. Maybe hardware store gas line hookup tube (the yellow stuff)?

Re: Flexible Deuterium Gas Input Hose?

Posted: Sun Dec 16, 2018 4:28 pm
by Rich Feldman
Well, Ian, here's a speculative suggestion.
How about narrow plastic or rubber tubing, for example the tubing that comes with toy PEM cell kits?
For the run between gas flow control and a not-too-hot junction close to fusor chamber.
165PLP_pd.jpg (3.01 KiB) Viewed 1293 times
Of course outgassing and permeation are a concern. Plasticiser and air molecules will work their way in and dilute the deuterium.
At what rate, compared to D2 flow that's said to be in the 10 sccm ballpark?

I think those unwanted diffusion flows will be about the same, whether tubing is under vacuum or small positive pressure (i.e. with flow restricting orifice downstream). For the latter case, an upstream flow limit would be good for safety. Then if gas hose popped off at the fusor end, and magically caught fire, it wouldn't writhe around and be hard to catch. :-)

Now let's wait for more experienced readers to set us straight.

Re: Flexible Deuterium Gas Input Hose?

Posted: Sun Dec 16, 2018 5:37 pm
by Chris Mullins
When I went from a needle valve to MFC, I also switched from 1/4" ACR copper tubing to stainless steel flexible tubing (and from standard Swagelok to VCR fittings). The switch was initially because my used MFC came with VCR fittings, but the flexible tubing made testing and installation much easier, and reduces stress on my chamber fitting (which is epoxied, not welded, so I'm always concerned about too much stress on it).

You can get 24" flexible tubing, with 1/4" VCR fittings on both ends for about $90 on ebay right now. List price for that ( ... -4-X-24FMR) is $242. There are cheaper deals on ebay that pop up, especially if you're "flexible" on the length or specific connectors. You could cut off an unwanted connector and possibly put a regular Swagelok fitting on. The flexible tubing I've seen usually has short straight ends that could be welded or used with a compression connector if you don't want the existing connectors.

Re: Flexible Deuterium Gas Input Hose?

Posted: Mon Dec 17, 2018 4:49 am
by Richard Hull
Proper metal flex with VCR fittings is super nice and highly recommended by the 1 person in 300 who use it from gas line.

Swagelock fittings with 1/8 copper common tubing for a few dollars has served me for years. I find it tough to believe that any form of "stress" on a properly installed gas fitting on a fusor could ever exist ever if hit by a hammer! A properly internally TIG welded swagelock fitting on as SS chamber cannot and should not come adrift or leak after being stressed by several hammer blows.

Richard Hull