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The barrel was the weekest part

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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The barrel was the weekest part

Unread postAuthor: tghhs » Mon Apr 05, 2010 9:24 pm

So i was out testing this launcher:
http://www.spudfiles.com/forums/tghhs-a ... 20207.html

After i'd just given it a new chamber and barrel, because it had a tinny leak through the front bushing that was annoying me. I used pn9 for the barrel this time though.

I took it up to 100 psi, like i always did and.... POP! hu????? looked at the pressure gauge; 60psi, hmm????? took a step back and looked at it; no problem there. pulled the trigger; all good, actuated just dandy. Looked inside the barrel, Oh F**K!

Has this happened to others? Here at SF, the common belief is that pipe can take more pressure if it's on the out side. Well, im not sure this is true, at least when a piston is pushed against it.

Was i a fool? should i have expected this? What do you guys think?
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Attachments
bummer.png
The barrel, after i took at apart.
Bent barrel out side gun.png
Inside barrel.png
Inside barrel 2.png
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Unread postAuthor: deathbyDWV » Mon Apr 05, 2010 11:30 pm

Well, that hasn't happened to me...

It seems like the outside would take less pressure than the inside since it has more surface area... But it also seems that the pipe, when pressure is on the outside, would try to compact together like an arch in a building, making it stronger... As long as there aren't any imperfections...
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Unread postAuthor: psycix » Thu Apr 08, 2010 10:12 am

Weird. PN9 should be able to hold 131 psi (from the inside).


Common belief is that a pipe is able to hold at least the same pressure from the outside as the inside.
But I guess that is not the case if it is deformed and became somewhat epileptic.

Any experts with a mathematical explanation nearby?
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Unread postAuthor: tghhs » Fri Apr 09, 2010 1:25 am

Yeah, that would make sense. I'm sorta thinking that maybe the barrel support could have slightly bent it out of shape, because it was quite a tight fit.

Also, because of the pretty extreme valve seat to diameter ratio, the piston would have been putting much more force on the barrel than most cannons.
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Unread postAuthor: absinthe » Fri Apr 09, 2010 1:40 am

i don't see how a pipe could handle the same pressure on the outside as the inside, as this demonstrates, you only need to crush the pipe on the inside on the outside it needs to rupture
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Unread postAuthor: ONEWING » Fri Apr 09, 2010 2:11 am

True abinthe, difference between crushing and exploding. Its like the ,pvie of the gas truck that imploded or a 44 gal drum that will implode when pulled to a vacuum, less then 1bar (14.5psi) pressure on outside. http://www.youtube.com/watch?v=Zz95_VvTxZM
http://www.youtube.com/watch?v=j3tqK6thgqU
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