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portable multishot pistonvalved cannon

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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portable multishot pistonvalved cannon

Unread postAuthor: charizzardd » Tue Apr 21, 2009 4:53 pm

the whole goal is to achieve several shots with this puppy... Im thinkin the main chamber will have an airtight piston, sealed with an o ring most likely... this will have a very strong spring behind it so that when you pressurize it from in front of the piston the spring compresses... then as the compressed air is used up for each shot the spring pushes forward hopefully maintaining a high pressure... The air fills up a smaller chamber and pilot area and is only allowed in via ball valve.. once the actual guns chamber and pilot are pressurized the ball valve is closed.... the gun is vented and piston actuated shooting the projectile... the ball valve can then be opened again and re pressurized closed and then shot again... Again the goal is to have each shot have the same pressure as the one before it, or at least close to it... what do you guys think? im just finishing up a piston valved gun, my first one actually... i may try to attach this system to it... hopefully the picture makes it more clear if its not already.

also sorry for its blurriness but you can still make out the words if you click the pic and open it in a separate window....also i know the photo is sketchy lol i just drew it in like 5 minutes... was bored of doing dynamics homework so i thought of this real quick : )

-charizzardd
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Attachments
IMG_7176.JPG
main chamber up top... schrader to the right then the ball valve is bottom right. to the left of the ball valve is a blowgun to vent the pilott, and to the left of that is the piston valve and chamber and barrel and what not...
0421092058.jpg
just added this... perhaps to address the amount of force required by the spring to keep the pressure up, i could use a small volume of air larger than the volume im planning to regulate... the larger diameter will provide a large force at not as high psi and the spring will just help... if i were to make it 3 inch pipe behind 2 inch pipe just filling it to 50 psi would supply 353 pounds of force... the spring would just help as the volume expands.. or i could possibly attach the spring on the other side of the first concept so it is pulling rather than pushing...
0421092058.jpg (26.8 KiB) Viewed 441 times
Last edited by charizzardd on Tue Apr 21, 2009 8:12 pm, edited 1 time in total.

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Unread postAuthor: twizi » Tue Apr 21, 2009 5:00 pm

it might work but why not just get regulated co2 and then have this setup and get alot more shots
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Unread postAuthor: charizzardd » Tue Apr 21, 2009 5:26 pm

Its always more fun to make it yourself i think. besides then i have to pay for co2 and a regulator... id rather just make it out of 5 dollars worth of parts and be able to use my compressor... or even scale this down and have it just attach to a smaller gun... maybe make a quick connect setup so i can carry more than one around and have lots of shots... would be pretty cool i think.
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Unread postAuthor: Lentamentalisk » Tue Apr 21, 2009 6:27 pm

Well you are completely off on the spring. The way you have it set up, it will do almost nothing to stabilize the pressure. What you need is a constant force spring, and realistically, probably twenty or so of them... If you think about it, in a 2" pipe, for the chamber, you will need 314lbs of force on the piston to keep the pressure at just 100psi. Far cheaper than trying to make this setup would be to invest in CO2...
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Unread postAuthor: Hotwired » Tue Apr 21, 2009 6:58 pm

Such springs do exist but they are a right bugger to play with.

I had a look at some when I was musing over the same theme of spring loaded piston in chamber a few months back.

I was not thinking of using it as a massive regulator though.
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Unread postAuthor: Moonbogg » Tue Apr 21, 2009 8:08 pm

I really like the creative thinking you have done here. Its a great. I'm not sure if it will work the way you are hoping for however. What I see happening is the spring simply adding to the pressure in the chamber by a small amount. You could just do away with the spring and pressurize your chamber a little higher, then get a few shots out of it that way, like a pre charged pneumatic air rifle.
This design you have reminded me of how a spring piston air rifle works. I thought maybe you could do away with the compressor and simply use the spring to slam the air through the barrel. It works well with air rifles, however, having owned a magnum powered air rifle myself (Beeman Kodiak) I know how how force it takes to cock that small spring, and thats with using the end of the barrel as a huge lever.
In order to get good power from a spring alone, you would need a monster of a spring and probably a 6ft lever to cock it lol.
Anyway, my point here is that theres no such thing as a bad idea. "Bad" ideas usually lead to good ones. So keep thinking. You are on a path to something good, I can feel it. Perhaps youn could do some simple testing with a really small, weak spring and just a tube or something like that just to get a feel for how it will behave. Pressure will certainly not be even for the different stages of spring compression. But using the whole spring for one shot would work provided you can cock it back.
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Unread postAuthor: psycix » Wed Apr 22, 2009 6:36 am

Actually, instead of a spring, you could use a air spring (compressed air). Now note, that when using an air spring, this is essentially the same as a chamber extension, but then with a piston in between!
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Unread postAuthor: sniper hero » Wed Apr 22, 2009 9:05 am

design it like a paintball gun
the chamber diagonaly and the small chamber as a grip :wink:

I like your thinking! :D
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Unread postAuthor: Hawkeye » Wed Apr 22, 2009 10:00 am

Just thinking out loud... You might be able to buy a "water hammer" which has a small pocket of air sealed behind a piston. If you attach that to the larger chamber it might work like you hope the spring will.
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Unread postAuthor: THUNDERLORD » Wed Apr 22, 2009 12:01 pm

I think it is a good idea with potential myself.
I was thinking similarly with my co2 tyre filler and about connecting a shrader in an endcap on a small piece of pipe, and having a plunger inside the pipe with water filling pipe on the other side , I could have a high pressure squirt gun.
I realized, I'd still have the same pressure that forced the water out left in the pipe that could still be used(work).

With gas stored as gas (as opposed to co2 cart.s which are like half liquid) as the gas is transfered the pressure drops.

I don't think the spring plunger chamber would yield 100% back since the spring will need to be atleast slightly weaker(?)
Looks like an interesting idea charizzardd. 8)
edit: for maintaining pressure consistency
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Unread postAuthor: charizzardd » Wed Apr 22, 2009 3:36 pm

thanks for all the positive feedback!!!! im making a basic gun as it is cuz its my first piston valve gun... i havent finished that one yet... im thinking i might figure a way to apply this to it... ill add some sketches soon lol thermo test friday gotta study!!!

-charizzardd
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