valveless gun, update with new videos

Show us your pneumatic spud gun! Discuss pneumatic (compressed gas) powered potato guns and related accessories. Valve types, actuation, pipe, materials, fittings, compressors, safety, gas choices, and more.
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trollhameran
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Tue May 13, 2008 2:27 pm

Ive seen topics made for valveless designs where the ammo is used to seal the barrel so that air cant escape untill a trigger is released letting the ammo through. So i thought id make a prototype as im hoping to use the idea for a shotgun design in the near future. the prototype is basically a short length of copper tube with a whole drilled in it for the trigger (a nail) to go through infront of where the ammo (a potato) will be. it took me literally a minute to make it and it seems to work quite effectively at 110psi, it smashes the potato into very small pieces, bear in mind that this is just using the potato to seal the barrel and the actual gun i make will have rubber seals inside the barrel.

Also im looking for ideas of how i can make the shotgun pump action but so far all my ideas have big flaws in them due to the valveless design, so if anyone has any ideas that would be great.



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Last edited by trollhameran on Thu May 15, 2008 3:45 pm, edited 1 time in total.
iknowmy3tables
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Tue May 13, 2008 2:43 pm

not that impressive, seals surprisingly well, one problem is the lack of any chamber volume
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trollhameran
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Tue May 13, 2008 3:10 pm

yh i will have a much bigger chamber volume on the gun when i make it but this was just a test to see if it would seal well enough to be feasable
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pat123
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Tue May 13, 2008 3:41 pm

cool, how much air leaks around the potato? it has to be one of the fastest opening and best flow "valves" if it doesn't leak.
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trollhameran
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Tue May 13, 2008 3:47 pm

a very small amount of air leaks out but im going to test it in a day or two with a rubber seal inside to see if that stops the leak completely
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jrrdw
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Tue May 13, 2008 3:56 pm

Sgort87 and I was kicking this idea around a little bit. I think you may be the first to build a working model. A potato held back 110 psi, how did you pull the nail out? a tow truck??? :shock: Here's what I drew up in paint about a year ago. --

Image
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FeLeX
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Tue May 13, 2008 3:57 pm

Nice man!! Didn't think potato would seal that good! Make it into a single shot sniper rifle! How much psi were the shots at??
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trollhameran
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Tue May 13, 2008 4:37 pm

jrrdw: the nail was quite hard to pull out, you could feel there was alot of force pushing against it from the potato. I think what im going to try to do is get a rubber o ring and put it in a coupler then have the barrel one side of the coupler and the chamber the other side so that the o ring is sandwiched in between the barrel and the chamber, hopefully that will help it to seal even better.

FeLeX: it was at 110psi
Im planning on making it into a shotgun but it will have interchangeable barrels so I will most likely make a sniper barrel for it as well.

Possibly going to try to make some custom rounds for it using the same principle as these bottle stoppers Image So that when the chamber is filled the pressure will force the round into the trigger and the round will compress and the rubber will be pushed out so that it seals in the barrel then when the trigger is released the round springs open so that the pressure can push it down the barrel.
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pat123
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Tue May 13, 2008 4:55 pm

I have an idea for the pump action part. have a tube with a 45 degree elbow below the barrel.put an oring across inside the pipe near the top to keep all of them from coming out. put a stick in the other side that seals in the pipe. this is too hard to explain i will post a pic.

i think this would work
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psycix
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Tue May 13, 2008 5:59 pm

@ pat123
I think that setup will blow out the "stick", and make it act like a pneumatic ram, and all balls will fly out too if things break.
Till the day I'm dieing, I'll keep them spuddies flying, 'cause I can!

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Eddbot
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Tue May 13, 2008 6:56 pm

what if you had a valve at the end of the barrel that worked on the same principle as a piston pilot, you load the projectile(think of it as the piston without a stopper), then close the valve at the end of the barrel, then pressurize the chamber, the valve at the end keeps the pressure in(like a blowvalve), then when the valve is opened the projectile is fire out the barrel like when a piston exhausts, but without a bumper to stop the piston, launching the projectile, the only problem i can see is finding a valve that uncovers the whole barrel fast enough
:edfirst:
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trollhameran
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Wed May 14, 2008 1:05 am

pat 123 i think i have an idea how i could make your idea work, ill draw a design for it then ill post it up here.

Eddbot: do you think you could post a pic of how your idea would be set up so that i can have a look and see exactly how it would need to be made for it to work
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daxspudder
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Wed May 14, 2008 1:21 am

so why not just use a burst disk, there is no valve involved, except the fact that you have to pressurize it somehow, like maybe a SCHRADER VALVE...
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trollhameran
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Wed May 14, 2008 1:40 am

to be honest i dont really understand how burst discs work
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Hydra
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Wed May 14, 2008 1:49 am

Pretty simple.
A burst disk is made from something that ruptures at lower pressures. WHen that pressure is reached, the burst disk bursts.. fulfilling its final job and all the air comes out. Its supposed to be the best valve in terms of performance and flow, but the worst in cost and management.
Its usually used in hybrids. There is alot of pressure already but the disk doesnt break. Now when you explode the pressurised fuel mix there are huge pressure which break the burst disk.
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