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Chamber Barrel ratio (Pneumatic)

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 Barrel ratio (Pneumatic)

Unread postAuthor: carl2.0 » Wed Dec 12, 2007 6:13 pm

Hey guys

I just want to know what is the chamber barrel ratio for pneumatics. I heard that combustions have a diff ratio
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Unread postAuthor: octane89 » Wed Dec 12, 2007 6:15 pm

Anywhere from .8:1 to 4:1. There won't be to much of a power difference, the big deal is how much flow you can have. The more air (cubic inches) and flow of it, the more power.
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Unread postAuthor: rna_duelers » Wed Dec 12, 2007 6:24 pm

Also how quickly you can flow the air,in other words valve speed and type has more of an impact on the power then the ratios.Anything above 1:1 in my opinion is good but also the pressure you are going to run it at also has an impact on the power achieved.

Got a rough design you want to throw at us?
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Unread postAuthor: bigbob12345 » Wed Dec 12, 2007 6:25 pm

Yea it really doesnt matter but supposedly 4:1 is the best ratio
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Unread postAuthor: rna_duelers » Wed Dec 12, 2007 6:38 pm

There is no 'best' ratio.Valves have a much larger impact on the performance of a gun then the ratios,if you were to open a 50mm ball valve and vent a chamber of say 1000cc into a barrel off 1000cc so the ratio of 1:1 you would get a velocity of X from the projectile,use the same chamber same barrel same projectile and pressure but use a 3/4 QEV that open in milliseconds and you would have a higher increase in velocity.

Ratios have very little to do with the power achieved and the efficiency of a launcher.
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Unread postAuthor: octane89 » Wed Dec 12, 2007 6:40 pm

With combustions, you build based on C:B ratios. With pneumatics, you build based on valve design.
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Unread postAuthor: DYI » Wed Dec 12, 2007 6:47 pm

At normal pressures, the "best" C:B ratio for pneumatics is around 0.2:1.
Obviously however, increasing chamber size will always increase performance. The .2:1 ratio assumes a fixed chamber size.
Please, download GGDT and save yourself the trouble of posting topics like these. I really don't know how people even design pneumatics without it.
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Unread postAuthor: bigbob12345 » Wed Dec 12, 2007 6:56 pm

And what would normal pressures be. Ive always heard the ideal ratio is 4:1 but I could be wrong.And your all right that the ratio hardly matters at all it is mostly just the valve flow and opening speed that matters so dont worry about the ratio just get a really good valve
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Unread postAuthor: Novacastrian » Wed Dec 12, 2007 8:10 pm

bigbob12345 wrote:And what would normal pressures be. Ive always heard the ideal ratio is 4:1 but I could be wrong.And your all right that the ratio hardly matters at all it is mostly just the valve flow and opening speed that matters so dont worry about the ratio just get a really good valve


You are right that you are wrong.
C:B ratios differ from person to person, it's a never ending argument.
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Unread postAuthor: DYI » Wed Dec 12, 2007 8:27 pm

The 4:1 thing assumes a fixed barrel size for some reason. It is near the point where the diminishing returns make increasing the chamber size any more pointless. But really, by increasing chamber size over 1:1, all you're doing is wasting gas. By normal pressures, I meant what your average compressor or bike pump can put out, no more than 160 psi. At these pressures, around 0.2:1 IS the perfect C:B ratio, assuming a fixed chamber size (which it usually is). There is no debate otherwise, because a larger chamber will always mean increased performance for a given barrel.
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Unread postAuthor: LikimysCrotchus5 » Wed Dec 12, 2007 8:45 pm

Rna_duelers the 50 millimeter might offer better performance only because the ball valve has a bigger flow rate even though it opens faster. But essentially you are right. it all depends on the cannon design. I kno i had a time where a 3/4 inch ball valve performed better for me than a 3/4 sprinkler.
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Unread postAuthor: Eddbot » Thu Dec 13, 2007 2:27 am

i think someone should do some experiments using a basic inline pneumatic, altering the c:b to to every whole number like 1:1, 2:1, 3:1, and use the same modded sprinkler in every test, just so we could get some baseline data for the C:B ratio debate. not me...way too expensive :munky2: ... monkeh!
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Unread postAuthor: jackssmirkingrevenge » Thu Dec 13, 2007 2:34 am

You can model it with GGDT to give you a rought idea of performance. In general, bigger chamber = better performance and more noise. By how much performance actually improves however depends on your valve, barrel length etc. - again, model it in GGDT to get an idea before you build.
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Unread postAuthor: ALIHISGREAT » Thu Dec 13, 2007 2:38 am

Eddbot wrote:i think someone should do some experiments using a basic inline pneumatic, altering the c:b to to every whole number like 1:1, 2:1, 3:1, and use the same modded sprinkler in every test, just so we could get some baseline data for the C:B ratio debate. not me...way too expensive :munky2: ... monkeh!


there is not really much point because the general rule is to put on a barrel as long as you can and uness you have a tiny chamber it should always give an increase in performance (although it may only be small) because in most pneumatics air is not exactly wasted but not used to its full potential because a few fps could be gained by having a longer barrel.
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Unread postAuthor: BigGrib » Thu Dec 13, 2007 6:07 am

i think the most efficient chamber barrel ratio for a pneumatic would all depend on your pressure you're gonna run. a 1:1 ratio would be most efficient if you were running at twice the atmospheric pressure would it not?? As Far as most powerful it doesn't freaking matter. power that damn thing up and launch some spuds!!!!!!
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