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Chamber Diameter vs Barrel Diameter

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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Chamber Diameter vs Barrel Diameter

Unread postAuthor: Gun Freak » Sun Apr 18, 2010 8:59 pm

Ok so me and Clemsonguy are discussing whether a 1.5" gold ball barrel will be choking the flow of a 1.5" chamber. I don't want to downsize the valve because I have all the parts measured out and I don't want to upsize the chamber to 2" because it would be way too big.
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Unread postAuthor: clemsonguy1125 » Sun Apr 18, 2010 9:03 pm

By the way the barrel is 1.5 SDR,
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Unread postAuthor: jackssmirkingrevenge » Sun Apr 18, 2010 10:45 pm

do the math ;)

compare (barrel inner area) to (chamber inner area - barrel outer area)
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Short fat chamber vs long and skinny

Unread postAuthor: Technician1002 » Sun Apr 18, 2010 11:11 pm

In general, the shorter and fatter the chamber is for a given volume, the higher the pressure remains through the shot. On a long skinny chamber, the gas must accelerate to the valve, encounter flow resistance, thus dropping the pressure on the way to the valve. Then high speed flow in the valve produces even more loss.

Higher pressure at the valve puts a higher volume of compressed air from the chamber into the barrel with less loss through the valve. In a short fat chamber the last 1/2 the air charge has a much shorter and lower resistance path to the valve. In a long skinny chamber, the path is long and restrictive.

In a combustion launcher, the shorter chamber has a shorter flame propagation path and less surface area to steal the heat of combustion for a longer lasting pressure spike from combustion. In this regard, a combustion chamber has that additional advantage when fat.

I hope this helps. This is one of the reasons we decided on a short fat chamber for the t shirt competition launcher. GGDT does not model that, but only uses chamber volume in the calculations. I wish it did so we could try to model different chamber configurations.

If this is insignificant and trivial performance changes or fairly major, I have no idea. I have not seen enough modeling on the subject to really know.

This is my 2 cents worth on the subject.
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Unread postAuthor: Gun Freak » Mon Apr 19, 2010 5:40 pm

So it isn't really worth upping the chamber size to 2" because the performance gain will be minimal...
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Unread postAuthor: irisher » Mon Apr 19, 2010 5:43 pm

gold ball barrel
If you can afford to shoot gold balls just buy Larda's cannon :lol:
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