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Help with semi auto pneumatic cannon valve...please!!

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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Help with semi auto pneumatic cannon valve...please!!

Unread postAuthor: lateral4 » Thu Mar 12, 2009 1:45 am

I have tried a bunch of ideas on paper to come up with a system that I can fire from a tank of compressed air or co2 without having to open and close or charge the valve. I could use some help on a design for a valve that would accomodate this. I thought about using a spring loaded piston valve but I don't know how efficient it would be. I want to shot potatoes only 50 to 75 yards but I want to be able to get the most out of my air. Any suggestions? Has it already been done and someone can guide me in the right direction. Thanks in advance.
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Unread postAuthor: inonickname » Thu Mar 12, 2009 2:21 am

Here we are again..

You want a hammer valve basically, which allows you to shoot from a single air source without using it all. Research "hammer valve" and you'll find what you need. Examples include Btb's 35 bar repeater, some paintball guns. Have a look through theories/accessories..it's full of them.
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Unread postAuthor: jackssmirkingrevenge » Thu Mar 12, 2009 4:47 am

inonickname wrote:You want a hammer valve basically, which allows you to shoot from a single air source without using it all. Research "hammer valve" and you'll find what you need. Examples include Btb's 35 bar repeater, some paintball guns. Have a look through theories/accessories..it's full of them.


As far as I know Brian's repeater used the hammer valve as a pilot.

For a large bore launcher, I think using a hammer valve directly is impractical. While brian used a hammer valve as a pilot, even a momentarily opened blowgun will do, I think a spring loaded piston is the best idea. If you want to limit waste, have a small chamber. At a decent pressure and with a good valve, 50-75 yards isn't going to require much air anyway.
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Unread postAuthor: inonickname » Thu Mar 12, 2009 4:57 am

I stand corrected- the hammer valve pilots a qev.

You can decide if the hammer valve is right for you- they're more ideal on a small scale and will require up sizing dramatically to work on this size.

An adaption of the piston valve may be best- for example spring loaded or the H.E.A.R.

(H.E.A.R.- Clide's GB Semi)

Edit: broken link
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Unread postAuthor: jackssmirkingrevenge » Thu Mar 12, 2009 5:20 am

inonickname wrote:You can decide if the hammer valve is right for you- they're more ideal on a small scale and will require up sizing dramatically to work on this size.


When you think about it though, a hammer valve that works on a commercial airgun has a tiny flow, but it's being held back by 4,500-3,000 psi of pressure. For spudguns using say 100 psi, you can make the valve much larger and still use the same size and strength of hammer.
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Unread postAuthor: SEAKING9006 » Thu Mar 12, 2009 8:43 am

Another idea is mounting the hammer valve on the piston itself and using the static wall as the striking face for the valve. Use a large diameter hose to run air to the valve and have it seal itself off from the barrel once it moves back a bit, in essence creating a giant blowback valve/bolt. Think of a hammer valve hitting a hammer instead of a hammer hitting a valve. This should allow for huge autos.
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Unread postAuthor: jackssmirkingrevenge » Thu Mar 12, 2009 9:19 am

SEAKING9006 wrote:Another idea is mounting the hammer valve on the piston itself and using the static wall as the striking face for the valve.


Interesting take, could you draw a diagram?
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Unread postAuthor: SEAKING9006 » Thu Mar 12, 2009 11:01 am

I have a drawing in a drawer. I might scan it next chance I get.

I'm in a really lax class right now on my BB.
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Unread postAuthor: SEAKING9006 » Thu Mar 12, 2009 5:26 pm

Ok, here we go. I just got all my stuff taken care of and I scanned the drawing I did a month or two ago This ones unmarked, most of my drawings have distinct markings on them.
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Unread postAuthor: jackssmirkingrevenge » Fri Mar 13, 2009 1:17 am

That looks like it would be do-able, though perhaps an overcomplication when a normal hammer valve would work just as well. Still, no reason not to have a play with it ;)
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Unread postAuthor: SPG » Fri Mar 13, 2009 6:41 am

Jack a normal hammer valve will work just as well, but what would you do to open it, if you have an inline system you end up with something like the Gunpower Stealth, and no hope of semi-auto. You could have the chamber below the barrel and have a U-shaped connector between the two but then you have dead space.

I suppose the advantage to this is minimal dead space, potential semi-auto if you balance the sizes and sprin right and of course a nice breech which could load from a magazine (but he's not drawn one of those).
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Unread postAuthor: SEAKING9006 » Fri Mar 13, 2009 11:07 am

Oh, a breech isn't very hard. What IS hard would be to make it reliable. A uniformly beveled cartridge sliding up a ramp made from the same size pipe can be done easily. I planned on studying my M1 carbine's extractor system and attempt to replicate it. There was a video posted a while back, a 1930's-40's introduction to fireams, that demonstrated a rifle going from nary a tube, up to a giant scale 1903 Springfield. Each and every part of it, too. A variation on my reverse hammer valve could seal at the breech itself, trapping gasses between the breech and piston. This would create a form of blowback bolt. However, it would only be most useful at the medium calibers (1.5in to 3in at the extreeme end) because there are systems better suited for use at the smaller calibers that can be more easily built at that scale.
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