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An Autopsy...

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Unread postAuthor: roboman » Fri Dec 26, 2008 10:52 pm

There was a gauge on the pump and on the cannon. And, yes, both gauges worked.
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Unread postAuthor: iisthemuffin » Sat Dec 27, 2008 12:22 am

If you want help roboman you should be honest. You condradict yourself. You said that "it was a possible" that your guage was in a single layer, then your pictures show it was certainly in a single layer. There is no way you were unsure about that.

Also, you said the gun fired on its own but then when jimmy said something about that, you said "you might have" fired it with your foot. How do you not know? Cannons dont fire on there own unless the valves fail and you didnt say anything about that either.

What i take from this is that you tapped thehole through a single layer and also fired your cannon carelessly even though you say you are so careful. A careful person would not accidently fire their cannon with their foot.

Its hard to believe that it ruptured when it was fired too. If it was fired it had somewhere to go. The air could have escaped out of the barrel but instead it busts through the pvc? I almost dont believe it. As soon as the valve was opened the force on the pipe was decreased. theres no way it would blow when it loses pressure?

Also, in your first picture, the nipple that threads into your adapter was broken atapart that was inside your adapter. If it were to blowout there wouldnt it have happend in part of the nipple that didnt have a piece covering it?

Something doesnt add up here. Im not acussing or anything but i honestly get a feeling that the cannon was dropped or that something that shouldnt have happened did happen.
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Unread postAuthor: TurboSuper » Sat Dec 27, 2008 1:05 am

I can't help but feel like it somehow flexed in a direction it shouldn't have. PVC may be strong, but it's also quite brittle. Mabye the water also created some kind of shock when responding to the high pressure. Ever hit PVC with a hammer?

Anyways, it seems like all these failures happen when people decide to shoot water, so it really begs the question: Why do people insist on shooting water?
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Unread postAuthor: frankrede » Sat Dec 27, 2008 1:13 am

TurboSuper wrote:I can't help but feel like it somehow flexed in a direction it shouldn't have. PVC may be strong, but it's also quite brittle. Mabye the water also created some kind of shock when responding to the high pressure. Ever hit PVC with a hammer?

Anyways, it seems like all these failures happen when people decide to shoot water, so it really begs the question: Why do people insist on shooting water?
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Unread postAuthor: starman » Sat Dec 27, 2008 1:26 am

TurboSuper wrote:I can't help but feel like it somehow flexed in a direction it shouldn't have. PVC may be strong, but it's also quite brittle. Mabye the water also created some kind of shock when responding to the high pressure. Ever hit PVC with a hammer?

Anyways, it seems like all these failures happen when people decide to shoot water, so it really begs the question: Why do people insist on shooting water?


I agree with you turbo. A flex force that fed back in the air chamber and ultimately caused by the mass and fluidity of the water ballon in the barrel. Also the rubber balloon may have had a significant friction and gotten "caught" in the barrel as it started out. I would have guess the barrel would have broken though.
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Unread postAuthor: psycix » Sat Dec 27, 2008 10:46 am

But why does a chamber blow when firing (aka venting pressure out of it)?

You sure you didnt just drop it or put it down hard?
That would make more sense:
Chamber takes a hit.
Chamber blows.
Pressure wave from chamber slams barrel.
Barrel connector breaks.
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Unread postAuthor: iisthemuffin » Sat Dec 27, 2008 7:06 pm

Exactly my point psycix. It just doesnt make sense. I feellike hes not telling us something.
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Unread postAuthor: roboman » Sat Dec 27, 2008 10:54 pm

I was holding it vertical when it blew up. While I was taking pictures, I noticed that the manual bleed switch was in the "open" position, which leads me to believe that an accidental triggering was the cause of this. I'm guessing that the recoil from the water was great enough to snap the barrel off. However, if the barrel snapped off, it should have vented all of the pressure from the tank, and the tank shouldn't have blown. When the valve is standing on end, the bleed switch is very easy to knock open with one's foot, or virtually anything else that brushes up against it. A wire broke off of my electronic trigger, and since I didn't have a soldering iron handy, I couldn't fix it while at the party. For the last few shots, I used the bleed valve as a trigger, which worked fairly well. The lever either rubbed up against my foot or some other object (rocks, etc.) and ended up triggering the cannon.

Basically, I am just wondering how the tank shrapneled, since there was no obvious cause.
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Unread postAuthor: nibbler125 » Sat Dec 27, 2008 11:52 pm

older spud guns will develop microscopic cracks in them over time and eventually cause it to explode depends how old the gun is. also if you wernt watching it someone could have accedently dropped it and thought no biggy and didn't tell you
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Unread postAuthor: roboman » Sun Dec 28, 2008 12:03 pm

The cannon was only about 2 months old. Also, one of my friends told the people who were holding it that it would explode if they dropped it, so they gingerly set it down and nobody touched it until we started shooting. :D
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