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multiple chambers

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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multiple chambers

Unread postAuthor: jon_89 » Fri Mar 20, 2009 7:44 pm

Would there be any benefits or downfalls to having multiple chambers? I typed the numbers in hgdt with two different chambers with eqaul volume and they came out to the same velocity.
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Unread postAuthor: psycix » Sat Mar 21, 2009 2:24 pm

For combustion guns you'd better have one big chamber instead of two small ones. This is because you would need a spark gap in each chamber, while one chamber with multiple would be more effective.
Also connecting the multiple chambers will make the gun unnecessary complex and may result in power loss.

A chamber with the same length as the diameter * the number of sparkgaps will theoretically be the best option when choosing between multiple chambers with the same volume.
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Unread postAuthor: jimmy101 » Sat Mar 21, 2009 2:40 pm

The other problem with multiple chambers versus a siingle chamber is that you increase the surface area to volume ratio. That means you'll loose more energy to heat loss.
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Unread postAuthor: rcman50166 » Mon Mar 23, 2009 9:15 am

However having multiple chambers will increase the life expectancy of the gun. An example is my "General". It has two 4 inch chambers which is the equivalent of a single chamber of around 5 and a half inches. Pipe at that size would get me worried about structural failure when it is fired at Sch 40. But I needed the power to propel projectiles out of a 3 inch bore barrel. So I had to use two chambers instead of one.
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Unread postAuthor: psycix » Mon Mar 23, 2009 6:22 pm

That just depends on the wall thickness vs the pipe diameter rcman.
If the wall thickness increases proportionally, there is nothing wrong with larger diameter pipe.
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Unread postAuthor: rcman50166 » Mon Mar 23, 2009 6:54 pm

yes that is true, but i don't recall any pipe that does that. With the pipe I'm talking about the pressure rating goes down. It's been a while but i think it's around 60 psi for 6 inch dia PVC while it goes up as the diameter gets smaller.
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Unread postAuthor: psycix » Tue Mar 24, 2009 12:37 pm

SCH40 (or any other SCH) means that the wall thickness stays the same, and yes, in that case, the pressure rating of larger pipes is lower.
However, SDR pipe is meant to keep the same wall:dia ratio. SDR=Standard dimension ratio.
Now you know a pipe that does that. :)
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Unread postAuthor: rcman50166 » Tue Mar 24, 2009 2:26 pm

Hmm.. curious, do they sell SDR at places like home depot or lowes or a major home improvement chain like that?
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Unread postAuthor: starman » Tue Mar 24, 2009 3:06 pm

rcman50166 wrote:Hmm.. curious, do they sell SDR at places like home depot or lowes or a major home improvement chain like that?


Yes, lately there has been .75", 1", and 1.25" SDR being sold at my local Lowes and Home Depot...no 1.5" unfortunately...pushing it as a cheaper alternative to sched 40, and 200 psi rating is still plenty for most house hold uses.

I found it a little thinnish for real plumbing work.
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Unread postAuthor: rcman50166 » Tue Mar 24, 2009 3:41 pm

So I guess they don't sell larger sizes, cause its the larger stuff that we're after. Like 4-6" ID pipe
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Unread postAuthor: Ragnarok » Tue Mar 24, 2009 6:36 pm

psycix wrote:SCH40 (or any other SCH) means that the wall thickness stays the same, and yes, in that case, the pressure rating of larger pipes is lower.

Afraid that's not actually true. The wall thickness of SCH 40 roughly doubles between 1/2" and 3" sizes:
http://en.wikipedia.org/wiki/Nominal_Pipe_Size

As you can tell, other sizes do the same.
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Unread postAuthor: psycix » Wed Mar 25, 2009 7:19 am

rcman50166 wrote:So I guess they don't sell larger sizes, cause its the larger stuff that we're after. Like 4-6" ID pipe

Go metal then.
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