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How to reinforce an air cannon?

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How to reinforce an air cannon?

Unread postAuthor: ThatGuy » Sun Oct 09, 2011 6:36 pm

I'm new to this forum but have been reading posts for a while

I've been looking for a list of easy ways to reinforce an pneumatic cannon to prevent an explosion or at least decrease the damage done

I have made 2 PVC cannons but I am afraid to use them because I saw a video of a PVC chamber exploding after being pressurized then shot with a pellet gun...

I plan on using one of my cannons as an airsoft shotgun and the other as a mortar- and I would prefer neither of them exploding in my face if they get shot or I trip. Both function under 100 psi and the lowest rated pipe used is 285 I think

Any suggestions on how to reinforce the chambers in a way that would make them stronger for under $30 each?
Any help is appreciated
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Re: How to reinforce an air cannon?

Unread postAuthor: PVC Arsenal 17 » Sun Oct 09, 2011 6:49 pm

ThatGuy wrote:I am afraid to use them because I saw a video of a PVC chamber exploding after being pressurized then shot with a pellet gun...


And that surprises you?

ThatGuy wrote:I plan on using one of my cannons as an airsoft shotgun and the other as a mortar


Make them with metal air chambers. There's no sense running around with a pressurized piece of plastic. For the effort it would take to "reinforce" one, you'd be better off using metal from the get-go. Grow some manly arms and lug around the additional weight.


I suggest a properly evacuated 1lb. propane bottle bored out and adapted to NPT threads with one of these:

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Unread postAuthor: nibbler125 » Sun Oct 09, 2011 7:17 pm

You can wrap the air chamber in a few layers duck tape. This is not a substitute for glue regardless of what the mythbusters say but in the event of an explosion the duck tape will keep the chamber together keeping the shrapnel all together and steady.
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Unread postAuthor: Gun Freak » Sun Oct 09, 2011 7:31 pm

I don't think duct tape will do anything significant lol :lol:
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Unread postAuthor: Gun Freak » Sun Oct 09, 2011 7:37 pm

I've always had this idea in my head to make pvc take higher pressure.
Basically there is a larger diameter pipe around the inner chamber. The outer chamber is pressurized to whatever pressure, say 100 psi. This makes inward force on the inner chamber, so in theory, twice as much pressure than the outer chamber can be added to the inner chamber. Does this sound right?
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Unread postAuthor: Technician1002 » Sun Oct 09, 2011 7:50 pm

Gun Freak wrote:I don't think duct tape will do anything significant lol :lol:


Mythbusters made a black powder cannon entirely out of duct tape. Enough tape will do the job.

[youtube]http://www.youtube.com/watch?v=3gio6k9KycM[/youtube]


These don't flow well. I recommend a higher flow between the chamber and barrel.
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Unread postAuthor: PVC Arsenal 17 » Sun Oct 09, 2011 8:17 pm

Technician1002 wrote:These don't flow well. I recommend a higher flow between the chamber and barrel.


That's why I suggested boring out the bottle neck and with that I implied doing the same to the adapter... or at least removing the stem from it. Done right, you can get porting close to that of 1/4" brass pipe. He could probably get off a few shots using the bottle directly as a chamber or have the bottle feed into a smaller, secondary chamber - A better option that wouldn't require flow modifications anyway.

Ideally the OP would follow your brazing instructions to get much larger porting from a propane bottle (assuming he's interested in a reliable, expedient pressure vessel). Propane bottles are great IMO.
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Unread postAuthor: saefroch » Sun Oct 09, 2011 9:08 pm

Gun Freak wrote:pvcpressurevessel.png
That'd work, though I see not the purpose of such a construction. Just get something with a higher yield strength :P.

In response to the OP: There's no reasonable way to reinforce them. If somebody's shooting at you with a pellet gun while you're playing airsoft, you have bigger concerns. Using only 100psi with 285psi rated fittings is quite, quite safe. The reason the PVC failed in the video is probably because of its poor impact strength. I've attempted to burst vessels far closer to their failure point with a pellet gun, and failed because PE and associated plastics have good impact strength.
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Unread postAuthor: ThatGuy » Sun Oct 09, 2011 9:16 pm

Sorry, I should have given more information-
The mortar has a 3in diameter chamber that's about 1.3ft long and that goes down to 1.25in diameter pipe that connects to the ball valve that connects to the barrel (1.25in diameter)

The shotgun is U shaped with the 1.25in diameter chamber under the 1in diameter barrel. This is the more sketchy of the two because the 1.5ft chamber goes down to .25in diameter pipe with two elbow pieces that go to a ball valve and then the barrel. its scay because the .25 pipe bends but I'm going to secure it so it can't move.

Because of all that I can't really make the chamber out of metal... Maybe the next cannon... But even then I don't have proper tools to work with metal and I don't know where to buy metal pipes bigger than 1in.

All I have at my disposal is: a power drill, a dremel, PVC, some screws/nuts/washers, and JB weld. anything else I would have to buy I am trying to keep under $30
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Unread postAuthor: Lockednloaded » Sun Oct 09, 2011 9:32 pm

Well since its obviously not going to be shot with pellet guns while its charged, dropping is the only real issue. Why dont you wrap the chamber in neoprene or a foam of some sort? the chamber's not going to rupture under normal conditions and pressures, so it doesn't even have to be strong enough to hold it together in failure mode.
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Unread postAuthor: saefroch » Sun Oct 09, 2011 9:57 pm

You'll also need PVC primer and cement to do the job properly, though you <i>could</i> use JB weld... I don't suggest it.

You don't need metal pipes larger than 1" or any special tools to make a spudgun out of metal pipes and fittings.

The 1/4" fitting isn't sketchy, but a bad design idea. It's a huge flow restriction, all the fittings should ideally not constrict flow any more than the barrel does, that's to say they shouldn't have an area perpendicular to the flow path that's less than the cross-sectional area of the barrel. Try to find larger elbows if you can.
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Re: How to reinforce an air cannon?

Unread postAuthor: jackssmirkingrevenge » Sun Oct 09, 2011 10:03 pm

ThatGuy wrote:I have made 2 PVC cannons but I am afraid to use them because I saw a video of a PVC chamber exploding after being pressurized then shot with a pellet gun...


I know what you mean, I no longer drive after seeing this video of several pounds of C4 detonated under a car.

Stop being such a pussy :)
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Unread postAuthor: ThatGuy » Sun Oct 09, 2011 11:03 pm

:idea:

I'll just surround it with camo tape to protect it from BBs and being dropped then.....
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Unread postAuthor: jackssmirkingrevenge » Mon Oct 10, 2011 12:45 am

saefroch wrote:That'd work, though I see not the purpose of such a construction.


... apart from the fact that should the jacket leak, you've created a "triggered burst disk" style thing.




Edited by BTB:wrong choice of words buddy. :D
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Unread postAuthor: saefroch » Mon Oct 10, 2011 8:42 am

Correct, but I don't honestly expect anyone to build that...
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