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Metal barrel sealing tee design

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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Unread postAuthor: Shrimphead » Tue Jul 18, 2006 11:15 am

The piston has to be bigger in diameter than the barrel so when you exhaust the pilot, there is air pushing on the other side to open it.
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Unread postAuthor: Brian the brain » Tue Jul 18, 2006 11:29 am

THe piston looks very good now.The only problem is the barrel just as big so I say get a slightly smaller barrel port.It wont restict flow noticebly.( You'll probably notice if you have an extremely long barrel)

In my shotgun the piston outer diameter is 26 mm, the barrel port OUTside ( cause that is what counts) is 22.It's almost too close.
I got away with it cause I use a lot of pressure.
The difference in diameter means the air has a surface to push on when the pilot is empty.
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Oh my friggin god stop being so awesome, that thing is pure kick ass. Most innovative and creative pneumatic that the files have ever come by!

Can't ask for a better compliment!!
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Unread postAuthor: )DEMON( » Tue Jul 18, 2006 11:48 am

When I blew into the chamber port the piston opened. The washer is bigger than the barrel. Is there no way this can work without a bigger piston? What do you mean by slightly smaller barrel port? ,do you mean I must get a smaller barrel?
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Unread postAuthor: Brian the brain » Tue Jul 18, 2006 2:11 pm

Well...that would solve the "problem"

The thickness of the tape around the piston is the only surface for the air to push on.If you say it works, it works...
It just seems like a very small surface.It might not open very fast like this.
Or maybe it will....
Just try it.If the valve doesn't open, you can always use the pvc as part of the piston, andt the metal fitting as the housing...( glue the pvc to the piston)

Try it the way it is now.
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Gun Freak wrote:
Oh my friggin god stop being so awesome, that thing is pure kick ass. Most innovative and creative pneumatic that the files have ever come by!

Can't ask for a better compliment!!
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Unread postAuthor: )DEMON( » Tue Jul 18, 2006 2:28 pm

Money is only expected in a few days. If the piston doesn't work than I will have to put the larger copper pipe and fitting back on. The piston is light, I filled it with epoxy putty(pratly putty). I am not sure of the forces involved when the piston opens, the simple logic is easy to understand but I have seen no hard research on this.The air can't only be pushing on the tape, I am sure it pushes on the sides and washer as well. I can't be certain.
I will post back when I have made more progress.

Would you try an ammo idea for me?, it is a shotgun style round which is basically a piece of pvc filled with metal balls(lead shot/bb's) and taped up each end. You will need a breech in your barrel and something to stop the round from being expelled out the barrel.
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Unread postAuthor: Brian the brain » Tue Jul 18, 2006 2:51 pm

Yes ofcourse the air pushes on all sides equally!.
but on the piston the forces even each other out.Pushing an equal amount from each side, means it wont move.
The tape makes the difference.
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Can't ask for a better compliment!!
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Unread postAuthor: Shrimphead » Tue Jul 18, 2006 2:54 pm

For your ammo idea if you just had the end of the barrel the right size for the cartridge then reduce it to the next size down so when it shoots, the cartridge can't move at all and the bb's go flying. But then you have to find a way to eject the cartridges. Maybe a repair coupling?
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Unread postAuthor: )DEMON( » Thu Jul 20, 2006 3:06 am

I am drilling out that brass fitting then gluing it inside. I will use 20mm pvc for the piston. So the it will be a 17mm+- barrel and a 20mm piston, will that be enough?
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Unread postAuthor: Brian the brain » Thu Jul 20, 2006 7:12 am

Yes it should be.
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Unread postAuthor: WOW!! » Thu Jul 20, 2006 7:49 am

Good job so far, I wazs wondering how do you connect the compresson fittings? Isnt there a little that goes inbetween the nuts?
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Unread postAuthor: )DEMON( » Thu Jul 20, 2006 8:55 am

It is alittle ring that fits over the copper pipe. You just tighten the nut on the fitting to make the ring permenantly fixed to the copper. Then you can remove it when ever.
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Unread postAuthor: Velocity » Thu Jul 20, 2006 11:54 am

nice valve... it really looks good!

A quick question... where do you get those large compression fittings? I looked on mcmaster.com, which usually has all of my spudgun parts, yet I came up with nothing :cry:
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Unread postAuthor: )DEMON( » Thu Jul 20, 2006 12:18 pm

Hehe, I am in Africa. You can not get these fittings :P It isn't even finished yet, I can do anything more until my mom gets paid next week. My 20mm piston is just going to be the small piston fixed inside the 20mm pvc, which fits nicely in the copper. It has taken soooo long to drill the fitting larger on the inside.
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Last edited by )DEMON( on Mon Jul 31, 2006 11:07 am, edited 1 time in total.
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Unread postAuthor: )DEMON( » Fri Jul 28, 2006 9:41 am

Ok, I have done a bit of work on this again.

Now I have added a bigger piston, exhaust valve(pilot), more galvinized fittings and a port for a female quick disconnect.

As you can see the piston housing after the valve(larger tee) is bigger. This is because the piston is now 20mm pvc. The people at the hardware store sold me irregular sized fittings which I can't get a link for, you can see that the piston housing needs to be linked. So what I have to do is get the two compression pieces and drill out the lip so the copper ring can still be there, then silver solder them together to make my own link. Too bad I don't have the tools to do that so I will have to find someone with them.

I have kept the space behind the piston to a minimum and it should work fine.
Check out the pics.
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Attachments
update-1.jpg
Things are progressing nicely.
Seen here is everything put together.
update-1.jpg (19.42 KiB) Viewed 763 times
update-2.jpg
Seen here is the open piston housing. This is the part I need to make a link for.
update-3.jpg
These parts are going to be the link.
update-3.jpg (17.07 KiB) Viewed 763 times
update-4.jpg
Here is the pvc piston and the rest of the body.
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Unread postAuthor: M3NT4L » Fri Jul 28, 2006 2:46 pm

:D Drooooooooling! i like what you did with this thing it is tuned to perfection and i have an estinguisher tank so i might try to replicate this idea with a few changes specialy a larger barrel!@@@!@!@!@ im hyped up.
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