Capillary tubing & connectors for chromatography for D2?

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Rich Feldman
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Capillary tubing & connectors for chromatography for D2?

Post by Rich Feldman » Sun Mar 11, 2018 7:03 am

Vacuum Technology seems to be the least inappropriate forum to discuss gas flow things.

At flea market this morning, I found what looked like a short optical fiber cable. Wasn't able to make a point of light appear at the center of a ferrule end. On closer inspection, we seem to have a capillary tube with some kind of 10-32 threaded connectors.
DSCN0143.JPG
Later I saw some possibly-compatible female connectors, with threaded plastic plugs to keep dirt out, on pencil-size stainless steel tubes for chromatography.

Does anyone here know what these connectors are called?
If the flex tube in picture is really 20 um ID, as hinted by the tag, it might serve as handy flow restrictor for pressure-regulated deuterium. (Mass flow controllers are unnecessarily high-tech.)

By the way, I had a seller space today and got rid of a ton of things, in exchange for little or no money. Had a bag full of the black objects which share the picture above. Instead of pricing the whole bag, I sold them by the foot & pleased a number of customers.
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Dan Knapp
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Re: Capillary tubing & connectors for chromatography for D2?

Post by Dan Knapp » Sun Mar 11, 2018 1:00 pm

These are indeed liquid chromatography fittings. I used these in my previous career. They are designed to hold very high pressure, but they will also work for vacuum, much like Swagelok fittings. Whereas the term “Swagelok” is often used generically for internally threaded nut ferrule fittings (like “Xerox”for copiers), to my knowledge there is no generic name for this type fitting other than “chromatography fitting.” There are multiple manufacturers of this type of fitting, and each tends to have its own ferrule design; so for best seal, it is critical to use compatible fittings even though the 10-32 threads will match. To overcome this compatibility problem, there are plastic fittings available that incorporate the male thread and ferrule in one piece. One of the major manufacturers is IDEX/Upchurch. Their catalog is a useful reference.
Tubing used with these fittings is available in very fine bore (to maintain chromatography resolution) so it could be used as a capillary leak for deuterium. The plastic chromatography tubing is usually PEEK, but fluoropolymer (“Teflon”) tubing is also used. If using fluoropolymer, one should be aware that some fluoropolymers are permeable to hydrogen. I don’t know about PEEK. Metal capillary tubing would be best. Although these fittings and tubing could be used for a capillary leak, connecting them to the rest of one’s system would require very expensive adapters that would likely negate any cost advantage.
Of possible use to the fusor group is that the plastic fittings can be used as a cheap low voltage vacuum feedthrough. You simply drill and tap (using a bottom tap) a hole in the flange using the dril end taper to form the ferrule seat. You then drill a smaller through hole to pass the insulated wire. The fittings are most often made for 1/16 and 1/32 inch tubing, so you use insulated wire with OD close to that. I’ve used these feedthroughs successfully for medium vacuum (millitorr range) ion sources, but never tried them for high vacuum use.

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Rich Feldman
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Re: Capillary tubing & connectors for chromatography for D2?

Post by Rich Feldman » Tue Mar 13, 2018 6:22 am

Thank you, Dan, for the prompt and very detailed response.

Here are two more unfamiliar connectors with 10-32 threads and tapered metal ferrules.

This one came from the flea market, I think, many years ago.
DSCN0168.JPG
Is the flat-tube section for heat exchange?

The other one is part of my new argon-flow setup. Had some ex-industrial regulator-gauge-valve sets from craigslist. This one was all-stainless, until I changed the cylinder attachment from some DIN thing to a CGA 580 nipple and nut.
DSCN0172.JPG
If the cylinder were standing vertically, instead of sideways, it would almost be tipped over by the weight of the regulator set.

I think its stainless capillary came from the unit in the first picture, or one just like it. The valve came with an adapter, MPT to something with 10-32 male thread and internally tapered sealing surface. I made an "unnatural coupling" nut, threaded 10-32 all the way through. Seems to make a good enough connection for the purpose, but probably isn't what the makers had in mind. At the tube's outlet end, a rubber hose carries argon at atmospheric pressure to a flowmeter.
DSCN0173.JPG
The metal tube ID is about 0.031". I had to barely crack the valve open to get a low enough flow. Then, remembering an old trick from fusor.net, I found a 0.030" diameter straight pin & inserted that into the straighter end of the stainless tube. That added enough of a restriction that the valve could be used as an on/off switch, with flow adjusted by the regulator pressure. Will need a more sensitive gauge, or more resistive flow path, to put a quantitative value on the pressure.
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Re: Capillary tubing & connectors for chromatography for D2?

Post by John Myers » Tue Mar 13, 2018 7:58 am

It looks like a gas chromatography column, but not sure why it would be flattened.

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Re: Capillary tubing & connectors for chromatography for D2?

Post by prestonbarrows » Sat Mar 17, 2018 3:59 am

Rich Feldman wrote:
Sun Mar 11, 2018 7:03 am
...
Outside of intellectual curiosity, is there any particular reason you are interested in such connectors/tubing Rich?

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Re: Capillary tubing & connectors for chromatography for D2?

Post by Richard Hull » Sat Mar 17, 2018 7:31 am

A nice coil of this capillary tubing makes a great gas flow restriction system choking off D2 flow rates so that a simple needle valve can control D2 flow into a fusor. About 5-10 feet in a coil is should do the trick and has been used by a number of fusioneers who can't afford a micro needle valve or a precision leak.

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