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Valveless ? 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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Will it work?

yes
5
83%
no
1
17%
 
Total votes : 6
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Valveless ? Pneumatic

Unread postAuthor: Spuddin » Tue Jun 10, 2008 7:58 pm

I got this idea from hotwired. so i drew a quick pic to see if u guys think it will work. should be cheap enough to make. the only special item would be the O-ring.
Hotwired wrote:A pneumatic.

It was a very odd design... it was a pressurised broom handle and the valve was a short plastic tube with one sealed end. Which was also the barrel.

Pushing the barrel further into the broom handle exposed holes cut into the side of the plastic tube and shot out the pencil or pen or whatever was in there.
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Unread postAuthor: n-strike » Tue Jun 10, 2008 8:03 pm

You lied! You said you wouldn't use a valve! You used a schrader valve! I'm just kidding. In all seriousness, I thought it didn't work at first, but then I read the "slide the barrel back and the air from the chamber enters the holes in the barrel and pow!" part. This might be a little retarded, but wouldn't it be kinda hard to push the barrel back with so much pressure building up behind it?

Happy 200th post, by the way.
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Unread postAuthor: Spuddin » Tue Jun 10, 2008 8:06 pm

i have no idea...
ok use a cork instead of the schrader valve.
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Unread postAuthor: n-strike » Tue Jun 10, 2008 8:07 pm

A little off topic, but where did the smiley come from? I swear it wasn't there the first time I looked at it...

And I was just kidding about the schrader valve part, but a cork...hm...
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Unread postAuthor: VH_man » Tue Jun 10, 2008 8:58 pm

technically this is a valve...... its the same valve used in inline Pump Paintball guns and the Airforce Condor..........

if you replaced the "pushing back" part with a hammer, youd have a kick-butt hammer valve gun.
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Unread postAuthor: SteelSovereignty » Tue Jun 10, 2008 8:58 pm

Looks like it might be okay, worth a test I'd say.
If your interested in this kind of operation you might want to check this link out:
http://nerfhaven.com/homemade/zero_semiautovalve/
made for nerfs, but pneumatics are all the same.

I'm not sure how good a moving barrel would be for accuracy, also maybe try to incorporate something to make it not waste all air in one shot?
Just suggestions, looks good!
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Unread postAuthor: clide » Tue Jun 10, 2008 9:46 pm

It will work, but it will take:

pi*.5^2*100 = 78.5 lbs of force to open at 100 psi.

The radius of .5 is used because the OD of 3/4" SCH40 is approximately 1"

I say it would be pretty hard to open.
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Unread postAuthor: Hubb » Tue Jun 10, 2008 10:22 pm

clide wrote:It will work, but it will take:

pi*.5^2*100 = 78.5 lbs of force to open at 100 psi.

The radius of .5 is used because the OD of 3/4" SCH40 is approximately 1"

I say it would be pretty hard to open.


What if the end cap on the barrel was replaced with a cone?
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Unread postAuthor: blind909 » Tue Jun 10, 2008 10:24 pm

Where would you find a cone that can be inside a pressurized chamber?
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Unread postAuthor: n-strike » Tue Jun 10, 2008 10:53 pm

Haha, I knew it would be hard to open! Unless you get someone to sit on it, but that would just shove it up there, and...ooh...AND NO NERFHAVEN! I WAS BANNED FROM THERE!
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Unread postAuthor: pizlo » Tue Jun 10, 2008 10:56 pm

Nit picking pizlo sees a problem here. You can't move it back instantly, so I figure your projectile will be out the barrel before your holes are a quater open. You probably willget bad performance because of this.
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Unread postAuthor: Hubb » Tue Jun 10, 2008 10:57 pm

I found this on the search.

I figured ant would have an answer. The only big problem I see is it leaking a bit when the barrel begins to slide (other than the hard opening).

As far as a cone goes, one could surely be improvised or machined.
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Unread postAuthor: Atlantis » Tue Jun 10, 2008 11:17 pm

This defiantly could be used for pneumatic cartridges, just shove this into the breech and the bolt would push the back in and the barrel would stop at the main barrel. A bolt/spring mechanism could help with the force needed. THis could also make a cool artillery style cannon with shells, let the weight of the main barrel on large calibers fire the valve.

P.S. A cone has the same horizontal cross section as an endcap so the same amount of force would be pushing in on it.
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Unread postAuthor: jackssmirkingrevenge » Wed Jun 11, 2008 12:41 am

Atlantis wrote:This defiantly could be used for pneumatic cartridges, just shove this into the breech and the bolt would push the back in and the barrel would stop at the main barrel. A bolt/spring mechanism could help with the force needed.


This is exactly how Saxby-Palmer air cartridges work, though they were replaced by the more compacy and "realistic" brocock tandem cartridges.
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Unread postAuthor: trollhameran » Wed Jun 11, 2008 1:43 am

Maybe if you could make the surface area of the cap behind the o ring really small if would make it a bit easier to push the barrel back. How big are the holes in the barrel going to be?
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