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Starting my advanced combustion tomorrow

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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Starting my advanced combustion tomorrow

Unread postAuthor: Rogue » Tue Nov 06, 2007 11:23 pm

i was going to build it out of all sch 40 pressure rated pvc. for the propane meter i was wondering if i coud just use pvc to build the meter.would that work.



features that it will have:

5.5ft long gb barrel
normal bbq ignition(will this work??)
a 3'long 4" wide chamber (overkill?)

and everything else normal




if i like the way this one turns out i will invest money in a stungun ignition and a clear piece of pipe(forgot name) for the chamber.


can anyone give me any other tips or point out flaws?



thatks,

roguE
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Unread postAuthor: cwazy1 » Tue Nov 06, 2007 11:33 pm

a pvc meter would work, but you gotta make sure that NONE of the liquid propane gets into the meter (either using a regulator or using a very long hose from the propane bottle to the meter.

BBQ ignition is fine.

a 3 foot long 4" chamber is WAYYYYYYYYYYY overkill and a waste of propane. with ur barrel size, a 1 foot long 4" pvc chamber is the perfect ratio.
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Unread postAuthor: Rogue » Tue Nov 06, 2007 11:44 pm

can you explain that pvc meter thing please?

so shoud i build it outta metal?
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Unread postAuthor: cwazy1 » Tue Nov 06, 2007 11:56 pm

well if you have a pvc propane meter (cheaper indeed), you will need to make sure that *liquid* propane does not get into the meter. the reason for this is because liquid propane is very cold and will make the pvc brittle and might eventtually cause it to explode when u fire the cannon or just when metering your propane. BUT. if you really wanted to use pvc (not advising it) you would have to prevent the liquid propane to get into the meter and only allow gaseous propane right?? well there are a couple of ways to do this: either use a propane meter like a burnzomatic and mod it or do the cheap method: instead of making the hose that goes from your propane bottle to your meter like 6 inches, make it like 2 feet so that by the time that the liquid propane enters the hose, it will be gas when it reaches your meter. understand??

if you build it out of metal, it will not explode because metal does not turn brittle when subject to cold. BUT if liquid propane goes get into ur meter, it will eat away at your teflon tape at the threads and will eventually cause it to leak. but theres no way around that so just be careful.

in general, metal is beter, more expensive, more weight. pvc will be MUCH cheaper but you just gotta be extra careful.

********liquid propane is in the bottom of your propane can, about 1/2 of the bottles volume is liquid. ***********
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Unread postAuthor: Rogue » Wed Nov 07, 2007 12:09 am

ok thanks. how much would a metal meter cost vs a pvc?

so if i used pvc i coud just make the hose like 2' long AND use pvc?
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Unread postAuthor: hi » Wed Nov 07, 2007 12:27 am

here is a picture of a meter i just finished tonight. I too am building an advanced combustion of about the same size. this only cost me about $20, minus the pressure guage which is about $7. so $27 total.

Image

in my opiton it looks better made of metal than pvc.
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Unread postAuthor: Novacastrian » Wed Nov 07, 2007 12:38 am

The name of the clear pipe you were thinking of is Polycarbonate :)
You missed one thing in your design- a chamber fan! Do you want an extra (approx) 30% bang or not 8)
Good luck with your build.
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Unread postAuthor: jimmy101 » Wed Nov 07, 2007 1:24 pm

Like Novac said, in order for a combustion to be "advanced" it pretty much has to have a chamber fan. The fan will boost performance more than will a meter pipe.

Nothing wrong with a PVC meter. Metal is great but hardly a requirement. A syringe
is even cheaper (and made of plastic) and just as accurate, but can be hard to find.

Double bevel the muzzle.

The chamber is way too big. The gun will perform better (give a higher muzzle velocity) with a correctly sized chamber.
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Unread postAuthor: Fnord » Wed Nov 07, 2007 1:44 pm

Alright, I'm gonna put this PVC meter thing to bed:

Pvc DOES become more brittle when it gets cold, but, in this case, brittle does not necessarily mean less strength, it means less impact resistance. Because meters are not subjected to shock loads like a chamber is, there is no reason why it should fail.

Don't hit it/drop it and you'll be fine. If you do, any explosions will be minor.


As to the rest: If you get a clear poly chamber, you MUST get a lighted LED fan. The lights will have a critical effect on your gun because they look cool :). If you know any computer geeks, talk to them. They may be able to get you one for free.

3 feet of 4" is overkill. I think theere might be a 1 foot piece of 4" clear pvc on ebay. It has been there for a long time.
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Unread postAuthor: cwazy1 » Thu Nov 08, 2007 7:29 pm

hi: that meter cost you 20$?? that is total bs..lol how much did those ball valves cost??
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Unread postAuthor: spudgunnerwryyyyy » Thu Nov 08, 2007 7:34 pm

Hey dude people get good prices and shop thrifty dont doubt them. I can get 1/2" ball valves for 4 bucks.
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Unread postAuthor: cwazy1 » Thu Nov 08, 2007 7:44 pm

haha then you're lucky! mine are 9$ ea.

but back onto the topic.
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Unread postAuthor: spudgunnerwryyyyy » Thu Nov 08, 2007 7:45 pm

Yeah pvc would work. But metal is way cooler.
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Unread postAuthor: BigGrib » Thu Nov 08, 2007 8:05 pm

Yeah the 3' 4" chamber is way too big mine is 2' 4" chamber and I have a 7' golf ball barrel and it is like .9 to 1 cb ratio i think for yours i'd go down to like 18 inches long. as far as your meter i'd go metal or here is my meter that works awesome
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Unread postAuthor: LikimysCrotchus5 » Thu Nov 08, 2007 8:58 pm

i kno this question is very noobish but considering i have never made an advanced combustion or a combustion in general, the guage on the propane meter is just a regular guage. And to meter your propane, you simply open the ball vavle and that lets in the propane and you fill until you are at a certain psi. Then close the ball valve, then open the other one and that lets in the propane you just metered into your chamber.
And i have another question. When you turn on the fan to mix the propane, doesnt that just push the air and the propane out through the barrel?

@bigGrib: oo :o so thats the kind of propane tanks people use. I see those at homedepot all the time. I thought that was some other type of fuel.
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