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My first pneumatic blew up on me!

Built a pneumatic cannon? Then post it here! This section is for completed, finished cannons that you have built. Please include pictures and information.
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My first pneumatic blew up on me!

Unread postAuthor: GrafixBoy » Sun Sep 23, 2007 8:26 pm

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this thing blew apart on me twice. i havent really gotten a good shot off yet because now I'm scared of it. I didnt let the glue set overnight or nothing when i pumped it up. i dont have a pressure gauge on it yet so i dont know how much pressure was in it when it blew. how long does it take to fill it up to good pressure? i pumped it up with a shop air compressor. not no rinky dinky bike pump. its a 4" tank workin its way down to a 1.5" barrel. Is the tank overkill? Home Depot didnt have any 3" pipe. if i add screws to the joints would that help. i put screws in where it came apart the first time with thread tape and it stayed together. the second time it came apart was at the top elbow where it comes out of the 4" to 3" reducer. im a total newb at this so give me your thoughts even if its just to tell me that im an idiot and i built it all wrong. BTW. I can build AK-47's all day long but this cannon has got me scared like a lil school girl now.
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Unread postAuthor: potatoflinger » Sun Sep 23, 2007 8:29 pm

It probably blew on you because almost all (maybe even all) your fittings are dwv. (not pressure rated)
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Unread postAuthor: GrafixBoy » Sun Sep 23, 2007 8:32 pm

what does the pressure do to it to make it come apart. its not exploding. just coming unglued.
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Unread postAuthor: thespeedycicada » Sun Sep 23, 2007 8:35 pm

dude scrap that death trap it has dwv fittings on it and i dont see primer stains wihich means it will go boom again.well actually if you already glued it it might not make a bond even with primer if you dont know what dwv is it basically means even if you gun seals you take it to high an KABOOM!! you have pvc shrap all over you.also is that chamber pipe even pressure rated i've never seen pressure rated pipe with black writing only cell core which is a VERY VERY bad thing.
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Unread postAuthor: HaiThar » Sun Sep 23, 2007 8:35 pm

Are you using primer and pvc cement? when you do it, you need to prime, and then you must use the cement and let it set for 24 hours.
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Unread postAuthor: spudgunnerwryyyyy » Sun Sep 23, 2007 8:37 pm

Ok, g-boy the fittings have surface area, pressure hits surface area making fitting come out. But this is because you are using dwv and dwv doesn't have deep enough sockets to have a good holding bond.
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Unread postAuthor: mopherman » Sun Sep 23, 2007 8:42 pm

ok dude, its three steps. Prime, Cement, cure for 24 hours. get some pressure rated fittings before you put it together. Also get a ten foot barrel, seriously. I would not want you putting together my Ak47.
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Last edited by mopherman on Sun Sep 23, 2007 9:00 pm, edited 1 time in total.
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Unread postAuthor: super spuder » Sun Sep 23, 2007 8:57 pm

umm one thing to say "B:C RATIO"
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Unread postAuthor: noob of noobs » Sun Sep 23, 2007 9:12 pm

You build AK-47's? For whom?
Anyway, everything everybody's said here is true. You're using DWV fitting which are notorious for blowing up, it doesn't look like it was properly assembled, and that looks like Cellular core pipe as your chamber. You're quite lucky, it's a blessing that you did use DWV fitting. If not, your chamber would explode, and those explosions are a lot worse (think schrapnel. :shock: ) Also, you'll probably have to order parts or settle for less on your chamber, since hardware stores seldom sell pressure rated pipe or fitting above 2."
Good luck.
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Unread postAuthor: GrafixBoy » Mon Sep 24, 2007 5:42 am

super spuder wrote:umm one thing to say "B:C RATIO"


what is the ratio?
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Unread postAuthor: frankrede » Mon Sep 24, 2007 6:43 am

GrafixBoy wrote:
super spuder wrote:umm one thing to say "B:C RATIO"


what is the ratio?
Notice he only replies to the least of his concerns.
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Unread postAuthor: GrafixBoy » Mon Sep 24, 2007 7:07 am

frankrede wrote:
GrafixBoy wrote:
super spuder wrote:umm one thing to say "B:C RATIO"


what is the ratio?
Notice he only replies to the least of his concerns.


my real concerns were already answered. the comment "umm one thing to say "B:C RATIO".... was vague. so yeah. i replied to that one.
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Unread postAuthor: thespeedycicada » Mon Sep 24, 2007 7:33 am

just take off the valve and make it over under but instead of using that giant cell core chamber use whatever your barrel is but only if its pressure rated!
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Unread postAuthor: psycix » Mon Sep 24, 2007 9:50 am

Scrap that gun!!
Its a death trap!!

-Fittings - DWV - will explode when above like 70psi
-Chamber - celluar core - you like PVC shrapnel inside your belly dont you?!
-How can the glueing pop off? learn to use PVC primer and cement!
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Unread postAuthor: MrCrowley » Mon Sep 24, 2007 10:00 am

I would ban you from ever building a spudgun again until you know what you are doing, but that's not possible for me.

My suggestion: Chuck the gun away, the whole thing, don't even think about building another one, spend at least a few months on spudfiles looking through all the pneumatic cannons on this website and researching how spudguns, pressure, gravity and physics work together to give you a safe launcher.

You clearly have no idea what you are doing, I will list problems with you and your launcher, it is your job to find out about them.

1) you have no idea what you are doing
2) you have no idea what you are doing
3) you used DWV fittings, they are not pressure rated, have short socket depths and are incredibly thin.
4) You have no idea what pressure rated fittings are
5) you can not read instructions on the back of the glue and primer cans
6) you don't know how physics or pressure work in spudguns
7) you don't have a guage to see how much pressure you have in the chamber

Thats all for now, I have more.
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