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9x mix and beyond Pneumatic cilinder

Post questions and info about hybrid (compressed gas with fuel) powered cannons here. This includes discussion about fuels, ratios, ignition systems, build types, safety, and anything else relevant.
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Unread postAuthor: paaiyan » Thu Jul 26, 2007 3:13 pm

UH, no. I just know that this is the easiest way to tell. Helium should be very good, it apparently only liquefies at very low temperatures.

OK, as far as I can tell, you'll never liquefy pure helium, unless you have an apparatus to cool it down to about -450 degrees Farenheit. So pretty much, if you're using a 9x mix, helium is your best bet. And good news! It's pretty cheap.
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Unread postAuthor: Intel Xeon » Thu Jul 26, 2007 3:33 pm

I'm talking straight out of my ass here, but I thought you couldn't burn helium, seeing as how it is an inert gas...
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Unread postAuthor: Jumpin Jehosaphat » Thu Jul 26, 2007 3:35 pm

Helium is a noble gas so it shouldn't be combustible... It would be even better than pressureized air or CO2 for pneumatics because of its light weight. You wouldn't want to use helium in a hybrid for the same reasons that you would not use CO2. Hydrogen is probably the best fuel for use in a hybrid, but I'm not sure where you can buy it in convenient compressed bottles.
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Unread postAuthor: Intel Xeon » Thu Jul 26, 2007 3:41 pm

So, what is with paaiyan's 'helium is the best bet for a 9x mix'?
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Unread postAuthor: Modderxtrordanare » Thu Jul 26, 2007 3:45 pm

Jumpin Jehosaphat wrote:Helium is a noble gas so it shouldn't be combustible... It would be even better than pressureized air or CO2 for pneumatics because of its light weight. You wouldn't want to use helium in a hybrid for the same reasons that you would not use CO2. Hydrogen is probably the best fuel for use in a hybrid, but I'm not sure where you can buy it in convenient compressed bottles.


People use helium in pneumatics due to is being a very lightweight gas, and allowing one to obtain better preformance from it.

In a combustion (or hybrid), you have to have something that burns. (obviously) A propane-air or butane-air mixture is what the majority of people use.

P.S. CO2 is denser than air.
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Unread postAuthor: Jumpin Jehosaphat » Thu Jul 26, 2007 3:47 pm

Well I would have thought he meant hydrogen except he mentioned it is cheap to get, but I think you have to make your own hydrogen which can be a pain...
A problem with helium and hydrogen both is that they are easy to leak. Any tiny pinhole leak will release gas, your solvent welds and threaded fittings have to be literally perfect.

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Modderxtrordanare wrote:People use helium in pneumatics due to is being a very lightweight gas, and allowing one to obtain better preformance from it.

In a combustion (or hybrid), you have to have something that burns. (obviously) A propane-air or butane-air mixture is what the majority of people use.

P.S. CO2 is denser than air.

True, helium's light weight can be used to get supersonic spuds without too much difficulty. I think paiiyan just got helium and hydrogen mixed up in his mind, no big deal.
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Unread postAuthor: paaiyan » Thu Jul 26, 2007 3:52 pm

Blarg. I lost track of what I was doing and was thinking straight pneumatic. Yea scratch that.
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Unread postAuthor: CannonBall » Thu Jul 26, 2007 3:53 pm

well producing hydrogen is no problem.
I ve got the hoffman device but i dont think hydrogen wouldn't be smart with oxygen
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Unread postAuthor: paaiyan » Thu Jul 26, 2007 4:13 pm

WEll, as far as I can tell, you can compress hydrogen that far without it liquefying, so it is viable. You just need to find out the most you can combust without going over your burst pressure.
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Unread postAuthor: CannonBall » Thu Jul 26, 2007 4:25 pm

well i might as wel use oxy acetylene....
i wrote burst pressure wrong at first post..
burst pressure should be around 100.000psi no way i could destroy my chamber right.... even with acetylene
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Unread postAuthor: DYI » Thu Jul 26, 2007 4:27 pm

Well, at 20x the mix will be detonating anyway, almost no doubt of that (unless you have a uselessly small chamber). It would be interesting to see how much abuse that 'indestructible' cylinder of your's could take. Hydrogen isn't usually as good a fuel as propane for many reasons (like the fact that it burns far more rapidly than propane, detonates with great ease, and has very low density), but propane probably isn't an option here (don't know if anyone has conclusively proven the truth of the partial pressure argument), so alternative fuels are required. However, if you can get gasoline to work and meter it precisely, it would likely be a slightly less grisly sight for the people who come wondering what the hell that noise was, and why little chunks of stainless steel mixed with the smoking remains of human flesh have been raining down for 5 minutes.
JK, but I think this 20x hybrid should be made out of something more impact resistand than stainless steel, like aluminum. REALLLY, REALLLLLY thick aluminum.
EDIT: Just saw the above post. You had originally said burst pressure was 725 bar, but 100,000psi burst pressure cylinder would probably stand a decent chance of surviving a 20x mix (just don't do 20x O2/H2 mix). How thick is that thing?
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Unread postAuthor: Jumpin Jehosaphat » Thu Jul 26, 2007 4:34 pm

You should be fine if the gun can really take that much pressure.
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Unread postAuthor: DYI » Thu Jul 26, 2007 4:40 pm

The chamber should be OK, but the fittings may be where you start to run into trouble. Steel fittings would likely shatter, and fittings made of other materials wouldn't be strong enough. Good luck getting C2H2 to 20 bar. If you try that, the gruesome scenario that I described in my above post may well become reality, especially if said C2H2 is mixed with air, or, god forbid, pure Oxygen.
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Unread postAuthor: Jumpin Jehosaphat » Thu Jul 26, 2007 4:50 pm

Does steel shatter? I think the only real trouble might be finding fittings that are the correct size, just what are you using for a chamber and can it easily be fit to normal steel fittings?
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Unread postAuthor: iknowmy3tables » Thu Jul 26, 2007 4:53 pm

well hydrogen is the best candidate for high pressure, but you really got to try a oxygen mix
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