Identifying Diff Pump Inlet Type

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.
Jerry Biehler
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Re: Identifying Diff Pump Inlet Type

Post by Jerry Biehler » Sun Sep 03, 2017 11:32 pm

Honestly, on the roughing side of things teflon tape is fine. Don't solder stuff, especially using regular solder, you need to silver braze.

Silviu Tamasdan
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Re: Identifying Diff Pump Inlet Type

Post by Silviu Tamasdan » Sun Sep 03, 2017 11:48 pm

Well I don't intend to solder directly the diff pump to the forepump if that's what you mean. :) I want to solder (or braze, but using solder would be easier) a KF-10 adapter to the diff pump outlet so I can use KF-10 hardware between it and forepump.
I've read in several places that using lead-tin solder is fine, especially on the low-vacuum side.
There _is_ madness to my method.

Jerry Biehler
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Re: Identifying Diff Pump Inlet Type

Post by Jerry Biehler » Mon Sep 04, 2017 2:37 am

Chances are the fitting is going to be stainless and that wont solder with standard solder. You either need silver solder or sil-phos.

ian_krase
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Re: Identifying Diff Pump Inlet Type

Post by ian_krase » Mon Sep 04, 2017 5:30 am

I prefer Loctite 290 because I can take it apart.

John Futter
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Re: Identifying Diff Pump Inlet Type

Post by John Futter » Mon Sep 04, 2017 9:56 am

Jerry
Hard Silver solder is not good for stainless where as ordinary solder works just fine
You have to have the right flux (killed spirits of salts with a 20 drops of Phosphoric acid added {and two drops of HF acidif you can get it})and not over heat the stainless, vacuum tight joints to 10 to the minus nine millibar no problem

Teflon tape is shit in the hands of the amateur I see this post has already slavered some other compond over the tape presumeably to try to fix a leak.
Teflon creeps so a leak that is sealed today will be a horrendous leak tomorrow.
The correct way to use it is to minimize the amount so it is used as a lubricant to allow the joint to be made by compression/ interference --not some huge amount of extremely slippery tape packing that moves to reduce pressure in the joint and allow a leak

We make Ln2 coolers for our systems and all use soft solder (60:40 tin lead) (you could use other soft solders especially those with a few percent silver) to join copper to stainless these joints go room temp to -197 Degrees C several times day
and do not leak according to our Helium leak detector, the final proof of ultimate vacuum of 2 by ten to the minus 8 millibar using a pfeiffer turbo.
If you use silver solder (hard solder silfos etc) it will crack sooner than later. Our experience a couple of weeks before a leak opens up, soft soldered joints now going ten or more years with no leaks.

Usually soft soldered threaded joints can be unwound by using a little heat (nowhere the melting point) and the bonus is you can redo them with out heating and they reseal perfectly.

I've only been doing this for forty years and no failures yet

ian_krase
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Re: Identifying Diff Pump Inlet Type

Post by ian_krase » Mon Sep 04, 2017 11:38 am

Wait, silver brazing lasts *weeks*? How big are these leaks?

Because that would suggest that my entire system would be leaking like a sieve which it isnt.

Silviu Tamasdan
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Re: Identifying Diff Pump Inlet Type

Post by Silviu Tamasdan » Mon Sep 04, 2017 12:22 pm

It may definitely depend on what conditions the joint is exposed to. If it goes through several cooling/warming cycles a day to LN2 temperatures, I can see how a stiffer solder could develop cracks where a softer one wouldn't. Whereas if it's more or less at RT all the time that wouldn't happen.

Thanks for the information everyone, it's pretty much in line with what I had been reading. I have experience with soft soldering (mostly for electrical work) so that would be an easier approach for me (though I've never done copper to SS before; I knew about that flux formula though). I did order a small amount of silver braze and flux and will be experimenting with it - I don't have oxy-acetylene equipment though, I hope a MAPP torch will work. The pump outlet is a 3/4" pipe connected to a several pounds mass of metal, so I may run into issues with heat transfer. If a regular torch doesn't work, I have parts to assemble an H2/O2 generator (fortunately those are relatively cheap and plentiful due to the "HHO" craze) and may use that to fuel an oxy-hydrogen torch.

John, about that flux. The only kind of HF I seem to find is 10% gel for dental porcelain etching, like this one: http://www.ebay.com/itm/PORCELAIN-ETCH- ... SwZ1BXegWW Do you think that would work in this application?
There _is_ madness to my method.

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Re: Identifying Diff Pump Inlet Type

Post by John Futter » Mon Sep 04, 2017 7:19 pm

Silviu
I do not like flame type soldering very much
If your MAP torch is heating a soldering bit OK
I use an electric 150 watt iron.
First I clean the area with a SS wire brush then using a cotton bud or similar
I coat the area to be soldered with flux
with a reasonable amount of solder on the bit I hit the fluxed surface and rub the bit back and forth
all going well the area should be perfectly tinned.
If you overheat the area you have to regrind all affected areas and start again

not sure about your gel
but alot of hardware shops sell glass frosting fluid (30% HF)

Ian
Yes a Fusor with hard soldered joints will fail due to the heating and cooling due to fusor runs
has alot to do with the differing contraction /expansion rates of the solder the SS and any other metal / alloy introduced

Jerry Biehler
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Re: Identifying Diff Pump Inlet Type

Post by Jerry Biehler » Tue Sep 05, 2017 12:59 am

HF? Be very careful with that stuff, goes right through your skin and attacks your bones. Then you get to have a calcium gluconate drip so it goes after that instead of your bones.

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