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Want to build first 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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Want to build first combustion cannon

Unread postAuthor: vng21092 » Mon Dec 09, 2013 8:46 pm

Is PVC strong enough to safely handle the expansion of the gas/fuel when ignited? Also, can the chamber be the same size pipe as the barrel as long as the volume of the chamber is larger/equal to the barrel volume?
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Re: Want to build first combustion cannon

Unread postAuthor: jackssmirkingrevenge » Mon Dec 09, 2013 8:58 pm

vng21092 wrote:Is PVC strong enough to safely handle the expansion of the gas/fuel when ignited?


If made sensibly, yes. Avoid thin walled pipe and fittings and make sure your components are correctly joined.

Also, can the chamber be the same size pipe as the barrel as long as the volume of the chamber is larger/equal to the barrel volume?


Yup, it doesn't even need to be equal - even half the barrel volume will do.

This is with the chamber volume at around 60% of the barrel volume:



Make sure you fuel it correctly, I recommend syringes: how-to-database/topic22301.html
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Re: Want to build first combustion cannon

Unread postAuthor: vng21092 » Tue Dec 10, 2013 3:21 pm

If 60 percent of the barrel volume is ok, then whats the point of some people going to 150 percent? (1.5:1) Just for power? And does primer really make that much of a difference? Can I just use PVC cement by itself? Also, because the gas/fuels can come from different sources, I'd assume they have different values when referring to combustion/expansion volume, how would I know how much to use with each fuel? I'm planning on using propane, is there like a method to find out?
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Re: Want to build first combustion cannon

Unread postAuthor: jackssmirkingrevenge » Thu Dec 12, 2013 5:03 am

vng21092 wrote:If 60 percent of the barrel volume is ok, then whats the point of some people going to 150 percent? (1.5:1) Just for power?


That and no love for efficiency ;)

And does primer really make that much of a difference? Can I just use PVC cement by itself?


You can try, but don't come cryin' when the thing asplodes in yer face.

Also, because the gas/fuels can come from different sources, I'd assume they have different values when referring to combustion/expansion volume, how would I know how much to use with each fuel? I'm planning on using propane, is there like a method to find out?


C'est tout dans le wiki: spud_wiki/index.php?title=Common_Fuels_for_Combustion_Spudguns
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Re: Want to build first combustion cannon

Unread postAuthor: vng21092 » Thu Dec 12, 2013 2:57 pm

You can try, but don't come cryin' when the thing asplodes in yer face.

... Would that really happen? I'm concerned now... I thought primer just softens the PVC so the cement would bond it better, would the joint be THAT much stronger with primer? O_o
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Re: Want to build first combustion cannon

Unread postAuthor: jackssmirkingrevenge » Thu Dec 12, 2013 3:23 pm

Why take the risk? Follow the manufacturer's instructions ;)
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Re: Want to build first combustion cannon

Unread postAuthor: vng21092 » Thu Dec 12, 2013 4:10 pm

only problem is... I already built the chamber without the primer, it's relatively small, 1 1/4'' x 6'', does the small size help at all? Smaller sized pipes are suppose to handle higher pressures right?
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Re: Want to build first combustion cannon

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Re: Want to build first combustion cannon

Unread postAuthor: jackssmirkingrevenge » Thu Dec 12, 2013 4:35 pm

I'm not saying it will explode, but an unprimed joint is weaker than a primed one. You might want to try it out from behind cover for the first could of times, with heavy projectiles to force pressure.
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