Well, I'm not new to building combustion cannons, but i am new to building pneumatic cannons, after i built mine yesterday, i let the glue dry until today and was just testing it at around 30 psi. or so. my question is, how high can i safely take the pressure? I'm deathly afraid it might explode in my face or something on it will fail, even though i made sure everything was glued correctly. One of the reasons I'm so afraid is that i can hear a small leak somewhere on one of the fittings, but everywhere else seems ok. i do know that the lowest pressure rated item in the design should be the sprinkler valve at (100 psi. ?), but i couldn't help myself not t go past 60 psi.
So, should i quit being a woosey and shoot it at 100 psi. ? lol
or...?
how safe is this thing??
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bigbob12345
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Check all your fittings and pipe to see if they say NSF-DWV. If they do then scrap the cannon and build another one with the proper fittings and pipe. If it says NSF-PW then it is pressure rated and you can take it all the way to 140psi before it starts getting dangerous.
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mafia_mike
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ah, sorry i forgot to mention those things.
all the fitting are pressure rated, and i used PVC primer and solvent to "glue" the pieces together
i do not have pictures of it yet, my camera's batteries decide to crap out every time i want to take a picture of something
all the fitting are pressure rated, and i used PVC primer and solvent to "glue" the pieces together
i do not have pictures of it yet, my camera's batteries decide to crap out every time i want to take a picture of something
That reminds me of my feeling with pvc, constantly crapping my (proverbial) pants at the thought of an explosion. I moved to copper and compression fittings, and i feel so relieved. If you're terrified like i was, just switch to metal, its cheap in the US.
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MrCrowley
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Is the leak in the PVC fittings or on a brass fitting/something else?
If it's on a PVC fitting you probably didn't twist the pipe and fitting 90 degrees when you glued them, by twisting them as you push them together you insure a perfect weld.
So if the leak is coming out of the fittings chances are you weld isn't as good as it could be and may be weaker then needed. It's up to you to decide whether or not you want to replace it or not.
If it's on a PVC fitting you probably didn't twist the pipe and fitting 90 degrees when you glued them, by twisting them as you push them together you insure a perfect weld.
So if the leak is coming out of the fittings chances are you weld isn't as good as it could be and may be weaker then needed. It's up to you to decide whether or not you want to replace it or not.
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mafia_mike
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the one leak that i can hear is coming from a 90 degree elbow in the back, at 60 psi. its a small whisper of a leak. all up and down the cannon ive put my ear to everything and that's the only place ive heard a leak. i had originally had two leaks (1/4'' fitting on my modded sprinkler valve) but i added more layers of teflon tape and that fixed that leak. really to be more specific do i need to be worried about anything rupturing if there is a leak?
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mafia_mike
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lol, i guess the reason why it makes me really nervous is because when i work with a combustion cannon, the pressure packed inside goes "boom" and then its gone. but with a pneumatic cannon , you have to wait for it to fill really slowly, as if its building suspense
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TurboSuper
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If you used NSF-PW fittings, then odds are the fittings will blow apart from improper glueing rather than grenading in your face.
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mafia_mike
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yes, i have all NSF-PW fittings.
i guess the question now is: its perfectly safe to take it to say 100 psi. or so ?
i guess the question now is: its perfectly safe to take it to say 100 psi. or so ?
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TurboSuper
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I take my cannon to 120 PSI regularly. If you built it right, it should be fine.
"If at first you dont succeed, then skydiving is not for you" - Darwin Awards
Mike it's 100% safe to take to 100. 120 would also be ok, anything above, and your risking a bit. The leak will not really affect the structural integrity.
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mafia_mike
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alright, safe of mind is all i need. actually the only other thing i need is fixing my C:B ratio lol. i first made it with a 10' x 2'' barrel, and a 10' x 3'' chamber (yes i know the C:B is way off but my friend and i were joking about how BIG it was) i do plan on getting a 3'' coupler tommorow and chopping the chamber down to prolly 3-4' or so
edit: (that c:b sounds about right doesnt it?...i'd like confirmation of that before i start cutting PVC!)
edit: (that c:b sounds about right doesnt it?...i'd like confirmation of that before i start cutting PVC!)
Last edited by mafia_mike on Sun Jun 22, 2008 10:24 pm, edited 1 time in total.
If you want to know what pressure you can use, you should check ALL your fittings and pipe and write down the pressure ratings.
The lowest rating is the pressure you can use in this gun.
The lowest rating is the pressure you can use in this gun.