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My 1st PVC Combustion Cannon

Built a combustion 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 1st PVC Combustion Cannon

Unread postAuthor: WWarrior234 » Tue Jan 31, 2006 9:31 pm

I just built my first potato cannon
Image
however i can't get the air fuel mixture right, for some reason it will not push a potato through all the way out. Oh by the way here is a picture of the firing mechanism.
Image
The Specs:
5' Schedule 40 PVC
3 Way elbow
2 Threaded end caps
Double prong grill ignitor
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Unread postAuthor: cardinals08 » Tue Jan 31, 2006 9:38 pm

where is the chamber? you are probably pushing the potato way to far down for it to go. with that you would only want to push the potato about 2 feet down, unless you have a smaller piece of PVC inside the bigger one.
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Unread postAuthor: WWarrior234 » Tue Jan 31, 2006 9:52 pm

Ah no there's no inner pvc and i was shoving the potato the majority of the way down the barrel, also i was having trouble getting my hairspray to ignite, the air mixture was not getting enough air should i drill rifling holes in the barrel?
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Unread postAuthor: WWarrior234 » Tue Jan 31, 2006 9:54 pm

oh and a lot of the air escapes from the holes i had to drill for the ignitor posts to go into the gun is there anything that i can seal that with?
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Unread postAuthor: sergeantspud2 » Tue Jan 31, 2006 9:58 pm

you need a bigger chamber, thats probably part of the reason its just not firing right. that was how my first gun looked and it always just "puffffed" out of the barrel. maybe you could buy some 3" pvc with a threaded end so you can screw it into the back where the plug would go.

did you use pvc glue?
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Unread postAuthor: CS » Tue Jan 31, 2006 9:59 pm

Damn! Looks like you need to work on your ratio to! That is like 1:6 ratio. Ill add more to my post in a bit I just have to go right now...
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Unread postAuthor: cardinals08 » Tue Jan 31, 2006 9:59 pm

well, you should have had wires on your ignitor, and you should have attached them to screws in your chamber that were close enough for a spark. I say get a piece of bigger PVC for the chamber, or get a smaller piece and make the smaller piece the barrel.
your C:B ratio (Chamber:Barrel) should be close to 1.5:1, your chamber should have a higher volume then your barrel, not the other way around. Not meaning to be rude or anything, but you have alot to learn about spudding
also, instead of double posting, edit your post
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Unread postAuthor: WWarrior234 » Tue Jan 31, 2006 10:55 pm

ok i'll keep that in mind from now on and the as for the ignitor two holes were drilled into the chamber and some end caps were put onto the posts to give the spark, i would post a picture but i can't get a good shot, I already tried. I originally planned to use plans for another gun that i had seen that would use the 3" PVC but i couldn't find any 40 schedule or any that were rated for psi so i had to go with the standard combustion and i didn't have any real plans, i was at school and they go crazy when you look up anything with gun in it so i had to search for potato cannon and i couldn't find any combustion plans so i made them up on the fly while at lowes purchasing my merchandise, and thanks for the ratio tip on the barrel.
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Unread postAuthor: K40T1C » Wed Feb 01, 2006 12:18 am

yeah dood that is defintitley to small of a ratio between the barrel in the chamber... the chamber should be about 1.5 times as big as the barrel
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Unread postAuthor: WWarrior234 » Wed Feb 01, 2006 12:54 am

Ok then i have a question about that, say i was to use an elbow piece and curve the chamber back around and through say a 3" piece of pipe on there how would I ignite that, or am i thinking the complete wrong way?
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Unread postAuthor: K40T1C » Wed Feb 01, 2006 1:17 am

u mean like doing a full u turn... you would need to use a larger diameter pipe because like i mentioned earlier, the ratio has to be 1.5:1... so if you used the same diameter, tha camber would be almost 1.5 time as long which would look kind of ugly... it would be extremley un orthodox but i expect it could be done some how...you would probably also want to have multiple sparks for a more even combustion... it would really be easiest to fix this if you simply put a chamber attached to the bck of the gun (using 4" or something) and just moved wired the igniter to the back...also i would suggest either using caulk or epoxy to seal the leak near the igniter because when u add the cahmber, the explosion will be more powerful and you may get hot gasses on you... ill try to make some type of drawing for you
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Unread postAuthor: WWarrior234 » Wed Feb 01, 2006 10:11 am

Cool thanks whenever just send it to me.
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