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Barrel to chamber 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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Barrel to chamber ratio

Unread postAuthor: AirGunNooblet » Fri Feb 10, 2012 6:55 am

Is there a certain barrel to chamber ratio which would give you maximum efficiency with the air?
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Unread postAuthor: jackssmirkingrevenge » Fri Feb 10, 2012 7:04 am


However it depends on:

- how fast your valve is

- how much flow your valve is capable of

- what pressure you're using

- how heavy your projectile is

So the one-word answer is GGDT ;)
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Unread postAuthor: Technician1002 » Fri Feb 10, 2012 10:55 am

Most of us do not try for maximum efficiency on air cannons. Maximum efficiency and maximum power are not really close together on the performance curve.

Maximum efficiency is where the pressure accelerating the projectile has fallen to zero as it reaches the muzzle. A really small chamber or low pressure is required for maximum efficiency.

A little more pressure in the chamber can provide a much higher acceleration on the projectile and provide significant acceleration all the way to the muzzle resulting in a much higher projectile velocity. A higher pressure and/or larger chamber requires much more stored energy which is lost after the projectile is ejected, so this is not at maximum efficiency.

I dealt with this quite a bit when designing a competition t shirt launcher as it was originally pumped up by hand.

We collected considerable in barrel acceleration data on that launcher.

I have found that the choice of the valve has a huge impact on efficiency and power. For an air cannon, a valve that provides minimal drag on the air flow is a huge factor.
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