by Doug Coulter » Mon Nov 22, 2010 5:00 pm
I have been looking at a little Pfeiffer leak valve (solenoid operated) and auto fuel injectors for this too. I don't think the thing you propose will work, or at least not unless it's not much pressure on either side of the valve. I may just try to make a solenoid/needle valve from scratch here, actually, we'll see. On-seat leakage is an obvious concern unless almost pressure welding forces are used, which has its own set of issues. It's still in the "I'm pondering the design" phase here. And "how to handle stuff so tiny, as it has to be to get the flow rates desired".
I did make a cool little ion source that would have looked a lot like that. I had gas coming out of the end of a .005" capillary tube, and a hole in a flat plate about .010" away, about a .020" hole.
At that point, the gas was still at fairly high pressure (didn't have time to expand to the tank pressure yet), and just 500v would light it off and ionize it, even at tank pressures in the e-5 mbar range. Looked like a little torch flame in operation, and trying it with N2, you could see physical separation between where the various spectral lines were emitted, as well as shock diamonds in the "flame". It looked about as cool as you could imagine (and probably was quite cold in fact). This was hard to keep working due to the tight spacings and sputtering though, so I went with the other one.
I also got a weird effect with diatomic gases that kinda freaked me out. After running that thing for maybe a minute, with maybe 5 watts in, the whole tank contents would produce a bright flash and the tank would go "tink" as if hit by a hammer -- at e-4 mbar pressures! I quit doing it, as the EMP that produced also killed things nearby, how, I haven't a clue -- wasn't much of a way for it to get out of the tank but it did -- a long chain polymer of N's that collapsed into N2? Not a clue -- It was a little too exciting for me though, and expensive when a PC a few feet away went up in flames. At any rate, I stopped doing things that way.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.