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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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An Autopsy...

Unread postAuthor: roboman » Mon Dec 22, 2008 4:59 pm

Yesterday, while at my friend's birthday party, he and I decided it would be fun to bring over my 2" pneumatic, to shoot water balloons. After we ran out, I decided to partially fill up the barrel with water. I've done this before, with no problems, however, apparently the cannon decided it didn't like me that day. While it was standing vertically, the manual bleed valve triggered, causing the air tank to explode violently, right around my pressure gauge. Fortunately, I was the only person near it at the time. The barrel kicked back, and hit me a place where no guy wants to be hit. Luckily, I had the barrel against my chest, which shielded my body from the shrapnel.

Any ideas as to how the tank split? It was made out of 2" sch. 40 PVC, and was connected to a 3/4" sprinkler valve. I only had 95 psi in it, and the PVC was rated for something like 200 psi.

I'll post pics ASAP.
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Unread postAuthor: JDP12 » Mon Dec 22, 2008 5:07 pm

my guess.... non pressure rated parts? until i see pictures i can't be sure.
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Unread postAuthor: roboman » Mon Dec 22, 2008 5:17 pm

Nope...I made sure to buy all pressure rated pipe and fittings.
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Unread postAuthor: MrCrowley » Mon Dec 22, 2008 5:20 pm

I'm guessing, without seeing pictures, that you have some small diameter fittings on the chamber maybe connecting the chamber to the valve, and that the recoil of the water in the barrel put too much strain on these fittings.

I'm guessing the pressure gauge was also close to these small diameter chamber fittings, and seeing as drilling a hole in a fitting weakens the part, the cannon decided to fail at that point.

Though I really have no idea without seeing a diagram or pictures. Did the tank actually split like you said or did it shrapnel?
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Unread postAuthor: JDP12 » Mon Dec 22, 2008 5:21 pm

another thing is that you could've screwed the pressure gauge into just the pipe, and not through a double layer
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Unread postAuthor: Gippeto » Mon Dec 22, 2008 5:27 pm

As we are "guessing", I'll throw my thoughts into the mix. :)

1) You tapped your pressure gauge into a single layer of pvc, thus creating a failure point.

2) "Less than careful" handling.


3) Temperature related weakness combined with #2. (Was it cold outside?)

Awaiting pics.

Edit: Damn I type slow. :(
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Unread postAuthor: roboman » Mon Dec 22, 2008 5:31 pm

#1 is a possibility, however, I am very careful with my cannons, thus eliminating #2. I live in SoCal, and yesterday, it was 72 and sunny.
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Unread postAuthor: Gippeto » Mon Dec 22, 2008 5:35 pm

Lucky, WARM bugger. :)

It's -25C here currently. (-13F).
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Unread postAuthor: raptorforce » Mon Dec 22, 2008 5:35 pm

i dont think 2inch pvc is 00 psi rated i have 1 1/2 inch pvs and its only ike 150 or something. So 2inch would have to be less then that so you were probably to close to the limit and ys maybe it didnt like you and got old and grumpy and couldnt take it any more and blew out
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Unread postAuthor: Gippeto » Mon Dec 22, 2008 5:37 pm

Really? The 1 1/4" stuff I have is rated for 370psi @73F.
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Unread postAuthor: roboman » Mon Dec 22, 2008 5:47 pm

I just found out... pressure rated @ 280 psi. The valve was rated at 125 psi.

Pics may be a while, Photobucket was (yet again) being stupid and wouldn't upload my files.
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Unread postAuthor: SP00K » Mon Dec 22, 2008 9:47 pm

another thing is that you could've screwed the pressure gauge into just the pipe, and not through a double layer


Aww crap.










It's okay, I'm building a cannon right now and I almost did that. Phew, talk about a close call. I've made that mistake before with disastrous results.
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Unread postAuthor: Xxplosive42o » Tue Dec 23, 2008 12:14 am

Definitely need pics before I can make an accurate assumption.

BTW, Where in socal do you live? I'm over in Burbank JFYI.
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Unread postAuthor: Hydra » Tue Dec 23, 2008 12:26 am

I think Mr.Crowleys guess is right.
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Unread postAuthor: Velocity » Tue Dec 23, 2008 3:30 am

I agree that pics would be helpful...though, no "damage shots" please :roll:
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