Fusor Forums

Hey all,

Been too long since my last newbie post so here's a new one.

I've been searching for a capillary line for my gas line and I've found this http://www.ebay.com/itm/Coiled-Tubing-3 ... 02&vxp=mtr

It seems to be brake line tubing made of 304 stainless steel 3/16" wide, here's the official product: http://www.summitracing.com/parts/aaf-all48040

Bottom line is: Is this usable for capillary tubing? It says that it's 3/16" tubing and that's 5mm. From Richard's FAQs he's said that the capillary line should only be around 2mm in diameter so it this too wide?
Also, if anybody could direct me to somewhere else where they got their restriction tubing, if it wasn't from a local shop but on the internet,, that'd be brilliant!

Cheers,
Tom

Hypodermic Tubing:

http://www.amazon.com/b?ie=UTF8&node=700776011

Stainless Steel 316 Hypodermic Tubing, 27 Gauge, 0.016" OD, 0.008" ID, 0.004" Wall, 48" Length $22.64
ebay item number 370775122864
-Peter

Alright, cheers guys, that's brilliant.

Tom

The attachment is the theory of choked flow pressure drops and it includes a table. Strictly speaking it is an alternate method of controlling flow.
-Peter

Capillary tubing is distinct from hypodermic needle tubing. For one thing, it is available in the smaller bore sizes that are required for decent flow control, e.g. 0.005" ID (or less, if you can find it). Conductivity is related to the fourth power of the diameter by Poiseuille's Law. Even a little bit bigger is going to waste a huge amount of gas. Capillary has a heavy wall and soft temper. Hypodermic tubing has a very hard temper. You cannot bend hypodermic tubing, and in this application you would need a very long length of it.

I have used, and I recommend, the following product if you want to go with capillary:

http://www.mcmaster.com/#51755K31

Capillary is frustrating to cut and prone to getting clogged. Note that there are good alternatives to capillary with comparable cost. Laser-drilled apertures (around 10 microns is good for D2) and variable leaks (many made by CVC, often seen on eBay for under $50) are some of the most reliable.

-Carl

Thanks for the chart Peter, though I don't know if I'll actually read through the whole thing - I took a quick look already and have it saved.

Carl, your suggestion seems very good and I can probably afford it, so at this time I think that'll be my choice unless something else comes up, but I'll make sure to look into the variable leaks.

Next question: Inner grid material, I'm looking for 30mm tungsten wire/cable on the internet but can't find it anywhere. Am I misplacing .30mm with 30mm or is it just hard to find?

Cheers,
Tom

There was a thread (no pun intended) here a couple years ago about using stiff capillaries,
with a wire threaded through the middle to reduce the gas flow area and width.
Seems to me that that offers some opportunites for flow control and for unclogging.

As Carl said, industrial applications have better ways to control small flows of gas.