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Vacuum Breaker

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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Vacuum Breaker

Unread postAuthor: spuzi14 » Sun Aug 17, 2008 3:09 pm

My summer job at a local school led to the replacement of a vacuum breaker:

<a href="http://s68.photobucket.com/albums/i39/playshackysack/Spudguns%20and%20stuff/?action=view&current=IMG_0290.jpg" target="_blank"><img src="http://i68.photobucket.com/albums/i39/playshackysack/Spudguns%20and%20stuff/IMG_0290.jpg" border="0" alt="vb2"></a>

That piece of metal just so happens to be a darn close shape of a combustion spudgun. I only say combustion because I love combustion veggie accelerators.

More pictures:

<a href="http://s68.photobucket.com/albums/i39/playshackysack/Spudguns%20and%20stuff/?action=view&current=IMG_0292.jpg" target="_blank"><img src="http://i68.photobucket.com/albums/i39/playshackysack/Spudguns%20and%20stuff/IMG_0292.jpg" border="0" alt="vb4"></a>


<a href="http://s68.photobucket.com/albums/i39/playshackysack/Spudguns%20and%20stuff/?action=view&current=IMG_0293.jpg" target="_blank"><img src="http://i68.photobucket.com/albums/i39/playshackysack/Spudguns%20and%20stuff/IMG_0293.jpg" border="0" alt="vb5"></a>

<a href="http://s68.photobucket.com/albums/i39/playshackysack/Spudguns%20and%20stuff/?action=view&current=IMG_0295.jpg" target="_blank"><img src="http://i68.photobucket.com/albums/i39/playshackysack/Spudguns%20and%20stuff/IMG_0295.jpg" border="0" alt="vb7"></a>

I understand how this item normally works on a urinal and I thought it may help me plug those holes and find a lid for this thing but so far I'm still stuck. I got the ignition fixed but I just can't figure out how to plug the back. I think it may be too thin to thread it. I was considering using a black plug like what you find in a stationary tub in the basement. I just wasn't sure how I would make it stay on. The inner diameter of the chamber section is really close to socket weld fittings for 1 1/2 inch SCH40 PVC. I think that's what I mean...I don't know, it's been way too long since I played with all this.

Any ideas on how I can plug the back of this cannon without loosing excessive chamber volume?
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Unread postAuthor: blind909 » Sun Aug 17, 2008 3:32 pm

Look at this diagram, pretty much self explanitory, And you fuel it by spraying your fuel down the barrel, or add a 1/4 inch ball valve to the end of the cap, and spray it through the ball valve. :wink:
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Unread postAuthor: spuzi14 » Sun Aug 17, 2008 3:52 pm

Ohh yeah...there is copper pipe. I forgot about copper pipe.

I was just going to shoot some propane from a Burnz-a-matic in there. No meter, just simplicity.
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Unread postAuthor: Radiation » Thu Aug 21, 2008 12:21 pm

cheaper and easier for spray and pray is this:

Image

This method requires the butane canister (preferably one with a plastic nozzle) and a used aerosol can. Take the nozzle off the used aerosol can, cut down the plastic nozzle on the butane canister to a size that will fit the aerosol nozzle from the used canister.

It's cleaner than right guard etc, it's fast and it's easy. I usually hold the bottle upside-down to spray out the liquid rather than gas as it is easier to measure IMO.
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Unread postAuthor: spuzi14 » Thu Aug 21, 2008 12:59 pm

I assume I can get that at Walmart or something?

Thanks for the suggestions. As soon as I finish my current cannon, I'll be working on this one.
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Unread postAuthor: marpat » Thu Aug 21, 2008 1:05 pm

blind 909s idea is quite close to mine only i would cut the slots off on the fat end and then just use some expoxy to put an end cap on it then possibly use a piezo that screws in and out
that way yuo can just choot your fueklt hrought the hole where the piezo goes

so fueling and firing would go like this
1 put in projectile
2 uscrew piezo
3. spray in fuel
4 rescrew piezo
5 fire
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Unread postAuthor: Radiation » Thu Aug 21, 2008 2:11 pm

spuzi14 wrote:I assume I can get that at Walmart or something?

Thanks for the suggestions. As soon as I finish my current cannon, I'll be working on this one.


Any where that sells refuelable lighters and even some places that don't. Cigar shops, cigarette stores, even grocery stores have them sometimes. They're about 2-3 bucks usually and don't require much more than the nozzle for the most part. If you get one with a metal nozzle just wrap electrical tape around it to the thickness of the inside of the used nozzle.

For small guns they're great, for larger guns they can be a total pain, but once you get the method they're much better for spray and pray than hairspray or other crap that makes you gun smell like a baked potato laced with perfume.
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Unread postAuthor: cdheller » Sat Aug 23, 2008 12:39 pm

A fairly simple way to convert your sloan urinal tailpiece into a simple combustion .
"acquire" the rubber vacuum breaker that fits in big end,cut so it extends past holes ,throw cut off bottom,plastic insert,cardboard friction ring aside.

The flange on top is 1 1/2 flanged drain ,the nuts (like under your kitchen sink ) have the same thread pitch and size as 1 1/2 ips .
It doesn't taper and seal on the threads though, the rubber top of vacum breaker does that.
although 1 1/2 nuts for drains will fit the ones on the bottom of a flushometer tailpiece on a toilet have 2 or 3 times the threaded length ,pvc ones slightly more also.edited to add (the nut that conects the tailpiece to the valve with the bottom shielding(?)might be a good plan)
1 1/2 cleanout plug on top w ignition threaded onto nut and your set.

firing should go something like

load ammo
stick butane nozzle in slot past rubber ,.fill
fire
stick toothpick sized object thru slot past rubber breaking seal
purge air w/ repeated passes of a ramrod/bore brush?
remove toothpicks and repete.

Hope this helps
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Last edited by cdheller on Sat Aug 23, 2008 7:00 pm, edited 1 time in total.
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Unread postAuthor: jimmy101 » Sat Aug 23, 2008 4:32 pm

:idea:
To me, the "vacuum breaker" looks more like a starting point for a reed pulsejet engine.
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Unread postAuthor: spuzi14 » Sat Aug 23, 2008 11:39 pm

I appreciate both of your replies. Cdheller, it never even occured to me to look at the style of fittings under my sink. I guess I've been away from the work bench for so long that I've become a bit dull as far as thinking outside the box goes.

Jimmy101...pulse jet never even crossed my mind. That's a tough choice, spudgun or pulse jet. I mean this thing would be perfect to make a small jet powered car. I wonder if I can get these things from anywhere else without having to buy the whole friggin urinal :x

EDIT:I know pulse jets get crazy hot. Will thinwall metal hold up to that?
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Unread postAuthor: SEAKING9006 » Sun Aug 24, 2008 8:58 pm

spuzi14 wrote:I know pulse jets get crazy hot. Will thinwall metal hold up to that?


There is no freakin way it will. I see videos of guys who built turbines out of turbochargers just for fun, without much research, and I watch as they crank it up until it glows red, and I'm literally sitting there going, 'Dear God, it's gonna blow up at any freaking moment. These guys have no [censored]ing clue what they're doing.'


It WILL melt/blow up.
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Unread postAuthor: spuzi14 » Mon Aug 25, 2008 2:21 pm

Well I don't know much about pulse jets but I mean I was concerned about it melting in on itself. I didn't think or I didn't know they could explode.
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