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Please check my math Chamber to barrel ratio ?

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Please check my math Chamber to barrel ratio ?

Unread postAuthor: tatfree » Fri Mar 12, 2010 11:27 pm

So far I have read on the topics of barrel to chamber ration from Page 133 on this forum all the way down to page 50 and it seems mixed on what to use for the ratio. I had heard a few times the rule of thumb seems to be make your air chamber volume the same CI as your barrel volume.
If this is correct for best performance I have put this together ,can you double check my math ?

1 barrel that's 2" Inside diameter and 24" long = 75.36"

2 chambers @ 1.5" Inside diameter and 21" long = 73.92"

I will be running anywhere from 10 PSI to 200 PSI max using a palmers regulator. I am also going to be using a 3/4 QEV with a ball valve if that matters.

Anyone see anything wrong with my math, and ratio ?


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Unread postAuthor: Crna Legija » Fri Mar 12, 2010 11:34 pm

i like to have a bigger chamber like 1.2/1.
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Unread postAuthor: Gippeto » Fri Mar 12, 2010 11:59 pm

Have you modeled your "creation" in ggdt yet?

The reality is that increasing chamber volume will increase power, but at a cost. (Dramatically increased gas usage for minimal velocity gains.)

I suggest you model it in ggdt, and swap variables until you reach your personal "balance point" with regard to chamber size/pressure, gas consumption, etc. and go with that.

1:1 is just a rough guideline IMO.

And I get 74.22 cu.in for the chamber volume. :)
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Unread postAuthor: tatfree » Sat Mar 13, 2010 12:04 am

I have tried going to that ggdt chart but it won't let me put anything in. Almost like it's an old link.

I will be using an on board 4500PSI nitrogen tank that's only 70Cubic inch when full, so I want to preserve as much air as possible :P

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Unread postAuthor: Gippeto » Sat Mar 13, 2010 2:16 am

You have to download ggdt and install it on your computer.

http://www.thehalls-in-bfe.com/GGDT/installation.html

Follow the directions.
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