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Would this work? (semi-auto BB gun)

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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Would this work? (semi-auto BB gun)

Unread postAuthor: Infernal Maveric » Mon Mar 26, 2007 11:49 am

Hi guys.

I was podering if this set-up would work at all.

Image

It would all be copper, but the huge chamber would be an old FE that I would empty and fit to the copper fittings.

The barrel would be 8mm pipe (6mm ID) and i would brobably need to sleev it with a 10mm pipe.

The other pipes would either be 22mm or 28mm piping which I have alot of.

Please tell me if its worth making, as I dont want to waste a weekend doing this just to find out it would never work.

Thanks,

Arpad
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Unread postAuthor: jackssmirkingrevenge » Mon Mar 26, 2007 12:44 pm

How exactly is the QEV piloted?

Something like this?
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Unread postAuthor: Infernal Maveric » Mon Mar 26, 2007 12:45 pm

It would be piloted by a Blowgun, but the pilot would refil from the preasure comming back from the chamber.
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Unread postAuthor: Hotwired » Mon Mar 26, 2007 12:47 pm

I guess the restriction of the BB barrel would help slow down the venting of the FE.

Then the pilot port could recharge from the small (it's going to have to be pretty small) bleed tube from the FE.

It's going to be a bit wasteful on air as the bleed tube to the pilot side will be open all the time when its only going to be useful when the blowgun is off.

A linked system to shut off the bleed tube when the trigger valve is open would be good.
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Last edited by Hotwired on Mon Mar 26, 2007 12:52 pm, edited 1 time in total.
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Unread postAuthor: jackssmirkingrevenge » Mon Mar 26, 2007 12:52 pm

In that case, it depends on the difference between blowgun output and the flow coming from the cylinder. The blowgun must have a larger flow than the refill tube, otherwise the valve will never actuate, on the other hand the refill tube must have sufficient flow to reseat the valve quickly otherwise your air will run out pretty soon.

It could be a difficult mechanism to tweak, I suggest you incorporate some sort of variable device on the refill tube (it doesn't have to be complex, could be as simple as a jubilee clip on a rubber tube) that will allow you to alter the rate of flow to get the system working well.
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Unread postAuthor: Hotwired » Mon Mar 26, 2007 12:54 pm

The vexing bit about this is I was thinking of a similar system only yesterday when I was fiddling with the two valves on the grip controls on my cannon...

It's all staying quiet though :P
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Unread postAuthor: Infernal Maveric » Mon Mar 26, 2007 2:08 pm

So i assume you mean that the bleed tube would need to be smaller than the 6mm tube right?

I realy won't be able to put a ball valve on the bleed tube as:

A it will be too small
B will defy the point of it being semi-auto.

And what is a Jubilie clip? Those plastic clips that you put ove a rubber tube in a hoispital ECT?
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Unread postAuthor: noname » Mon Mar 26, 2007 4:33 pm

Just use a blowgun as a main valve, it'll last longer and be cheaper.
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Unread postAuthor: Hawkeye » Mon Mar 26, 2007 5:32 pm

I think you're better off with a piston valve and the chamber in the position of a stock with a smaller firing chamber where you have the extinguisher. You could have it set up with a small one way valve at the neck of the extinguisher. The one way valve could share a spring with the piston. When the piston slams back it will hold the one way valve shut and then release it as it bounces back. The pressure differential will then allow the one way valve to open and refill the firing chamber.
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Unread postAuthor: hi » Mon Mar 26, 2007 6:25 pm

I think that the bb's will jam up in the feeder, maybe a clip would be better
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Unread postAuthor: jackssmirkingrevenge » Mon Mar 26, 2007 9:27 pm

noname wrote:Just use a blowgun as a main valve, it'll last longer and be cheaper.


For a 6mm launcher that's probably the best idea.
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Unread postAuthor: spudthug » Mon Mar 26, 2007 9:34 pm

DO NOT WASTE A QEV+A FIRE EXTINGUISHER ON A BB GUN!!!!!!

ok now that my rage is over...did u get this idea from my post when a-98 made those diagrams??jsut wondering...if u r going to do this make it for a bigger barrel for paintballs or marbles...plus a qev and that fe at 100 psi would most likely blow that barrel off...

oh and u CANT use regular fittings in a FE it is a special machine thread..u can use 1/2 fitting but only iron!!!! u cant wel/solder copper to anything but brass and copper (that would be safe) and u especially cant solder copper to iron...make the fitting iron and nothing else...look at my gun just look for a pneumatic posted by me a few days ago....it is lockd becaue i got into a fight but look at the first page...



EDIT: i didnt read the psots somebnody may have pointed this out but im tired so im not going to...u cant make a qev semi auto....it has no sealing mechanism after it lets it all go....
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Unread postAuthor: noname » Mon Mar 26, 2007 10:30 pm

Bet ya 50 bucks you can. :wink:
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Unread postAuthor: frankrede » Mon Mar 26, 2007 11:28 pm

Why not use a 1/8"QEV?
They would give you more shots and plenty power?
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Unread postAuthor: Killjoy » Tue Mar 27, 2007 12:16 am

Im with noname spudthug, if you set you mind to it, anything is possible (Well not anything but yeah whatever). This design is possible it will just needs a little tinkering.
Heres my idea, get two ball valves, and move the handle on one so they line up, but when the pilot valve is closed, the valve to the chamber is open, but just barely so that when you open the pilot valve, the fill vlave will close almost instantly. You could then use a spring to close the valves once you release pressure on the handle of the pilot valve.
You would probably have to grind down the little lip on one valve which prevents it from turning 360 degrees. Let me draw a pic.

Edit:Nevermind i just remembered how much i suck at making diagrahms that are understandable, if you don't get my idea then just forget i mentioned it (probably wouldn't have worked anyways).

By the way, good diagrahm infernal.
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