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Multishot cannon wont ignite.

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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Unread postAuthor: Ragnarok » Wed Dec 10, 2008 9:13 am

whitewolf wrote:So in fact the way I did it was more safe than if I had of sealed the whole thing up.

No, it really wasn't.
The whole point of these cannons operations is that the pressure is directed through the breech and into the muzzle. Doing any thing other than that defeats the point of operation, and causes other areas of hazard - in this case, a wildly flying plumbing fitting.

What would have happened if all the pressure could not have escaped through that little hole within the fraction of the second that the explosion took place? It would have blown the cannon up.

Again, no it wouldn't have blown up. The cannon's materials are capable of withstanding the pressures generated by the combustion of such a mix for an indefinite amount of time, far longer than the pressure peak will last.

It sounds to me like you're trying to justify your, to be frank, poor decision with a retroactive explanation for why you did it. None of your justifications hold any water for us, because we've spent many years gluing cannons, and then - Shock, horror - not having them explode.

I am more worried about it exploding AFTER I seal it up, because in that situation there is no telling which part of the cannon is going to fail, and how.

Half true (likely points of failure can usually be identified well in advance of any event, but being certain is unlikely), but the point is, that with a well built cannon, there should be absolutely no failures anyway.

Not gluing on a fitting ensures you know where it's going to fail - it also ensures you know when, which will be the next (and every) time you fire it - and completely voids the point of the cannon.

It's simple maths.
My cannons that have been glued completely: 0 destructive failures per shot, the ideal.
Your unglued cannon: 1 destructive failure per shot, the worst possible.

focusing it all in one spot, which might have been my eyes or my hands.

If you're fretting over that, (a very unlikely event in the first place) wear safety goggles - which you should really be doing anyway.
Your hands might get minor burns, but shouldn't be unduly injured by the short burst of heat - you can also wear gloves if you want.

Radiation wrote:in such an unsafe manor

Unsafe manor? You mean, like it's got weakened floorboards, a haunted cellar or a murderous butler?

Sorry, but while the rest of your post was fine in terms of language, you got a little muddled up there.
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Does that thing kinda look like a big cat to you?
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Unread postAuthor: jrrdw » Wed Dec 10, 2008 12:39 pm

Ok guys thats enough picking him apart now. The importent thing is he learns by the mistake he made and I think it's safe to say he's been told.

Now solvent weld it back together, give it a name and put up some damage pics.
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Unread postAuthor: Ragnarok » Wed Dec 10, 2008 1:05 pm

jrrdw wrote:Give it a name

I suggest Delilah, Jessica, or Stephanie.
If you don't like those, you could go with Sarah or Andrea.

Far more original than all of these 'destructive' names like "Kill-o-spud 5000".
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Unread postAuthor: jimmy101 » Wed Dec 10, 2008 1:16 pm

whitewolf wrote:Yes yes, but hear me out first, its not that simple. If I had of glued it, where would all the force have went? The force would have had one way to escape: the small hole that is the muzzle. My muzzle is much smaller than the ones I see on this site.

What would have happened if all the pressure could not have escaped through that little hole within the fraction of the second that the explosion took place? It would have blown the cannon up.

Hang in there whitewolf, were not ripping you a new one just for fun (though it is fun to give newbies a hard time :twisted: )

Foks around here have been doing this for a long time. Several are very serious about understanding what makes a spudgun work, how it works, the pressures involved, the pressure rating of the parts used, how to get the most pressure given a particular set of parts etc.

Knowledgeable spudders design their cannon so that they will survive the worst case scenario. In a combustion gun that would be what happens when the ammo jams in the barrel. The "gun" is now a closed combustion chamber. There are no exits for the pressure created by the combustion process. The gun is designed to withstand this worst case scenario with out blowing up, comming apart, cracking or in anyway damaging itself or the operator.

Indeed, if you ignite propane + air in a closed, properly glued PVC chamber pressure will peak at less than 120 PSIG. Well within the pressure rating of pressure rated PVC. (Indeed, 120 PSIG is less than half the rating of the most common sizes of pressure rated PVC.)

Heck, I've done many closed chamber firings. The chamber doesn't even make any noise when it combusts. Even in a sealed chamber the pressure only persists for a second or so after ignition. Heat trasnfer from the hot gases to the chamber walls drops the pressure back to 0 PSIG within a second or so. The PVC only heats up a couple degrees, barely enough to detect with your hand.
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Unread postAuthor: jrrdw » Wed Dec 10, 2008 1:30 pm

Ragnarok wrote:
jrrdw wrote:Give it a name

I suggest Delilah, Jessica, or Stephanie.
If you don't like those, you could go with Sarah or Andrea.

Far more original than all of these 'destructive' names like "Kill-o-spud 5000".[/quote]

Wish I'd thought of that! All girl names Rag, come on now. I don't see you naming any of yours a girlie name! :twisted:
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Unread postAuthor: Ragnarok » Wed Dec 10, 2008 3:00 pm

jrrdw wrote:All girl names Rag, come on now.

Well, you want to give it a boys name?
Surely someone (we probably know who) would comment on a matter like "shooting off" - or just something like that.

I don't see you naming any of yours a girlie name!

You evidently don't know what the last combustion still in my collection is called then. :tongue5:

Wish I'd thought of that!

If you want to call a cannon "Kill-o-spud 5000", go nuts. ;)
Perhaps write it down the side in fancy italic script if you're really dedicated.
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