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Barrel Sealing Valve Question

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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Barrel Sealing Valve Question

Unread postAuthor: tmacd995 » Fri Mar 14, 2008 1:44 pm

Hi all,
I am working on a barrel sealing valve like the one on BCVids. It is a 2" tee and I am trying figure out how far to insert the 1 inch pipe through the bushing? (Picture below)

Image

Also I can't figure out whether the piston itself should be flush with the sides of the tee?

If it was, how would air get to the chamber?

Thanks in advance for your help

Heres a pic of the whole thing, if that helps?
Image[/img]
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The back part

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Unread postAuthor: Jared Haehnel » Fri Mar 14, 2008 1:51 pm

I would place the end of the barrel just past the tee. The piston should fit tightly in the tee but still allow air to blow by it unless you want to drill a pilot hole to equalize the pilot chamber and the main chamber.

I would put a separate fill on the main chamber and fill it from that side rather then fill it from the pilot chamber side. But thats just personal preference.

There's a few posts on piston valve designs you might want to look in the pneumatic forum and in the how to section...they list some good idea's

Other wise it looks like you've got a good start to your gun 8)
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Unread postAuthor: bluerussetboy » Fri Mar 14, 2008 3:37 pm

Personally, I like to have my barrel's sealing face in the center of the tee. As for how tight your piston should be, make it fit as tight as possible but can still move smoothly. I like to make epoxy pistons tight and then sand them down to where they just barely move with 1-2 psi. That and a small pilot volume and sometimes I can pilot them with a presta valve. :lol:
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Unread postAuthor: tmacd995 » Fri Mar 14, 2008 4:36 pm

Thanks to everyone for their help, its all glued up in my shop, just have to wait a long 24 hours before I can test it...

The port size was 1 inch because I am doing a performance comparison on different valves. I now have a 1" ball valve, 1" Electrically acuated sprinkler, Modified sprinkler, and this. They all have the same chamber to barrel ratios. I realize thats alot of guns and that the piston will work best, but it keeps me entertained.
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Unread postAuthor: elitesniper » Fri Mar 14, 2008 5:28 pm

well it put my pipe just a tiny bit past the tee as seen here http://www.spudfiles.com/forums/2-piston-1-5inch-porting-finaly-done-t12817.html

just because i feel there is more flow :)
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Unread postAuthor: lockmanslammin » Sat Mar 15, 2008 12:59 am

looks good so far tmac. Make sure the end of the barrel that the piston will be sealing against, is as square and polished as possible for the best air tight seal. As far as the piston being flush..... What you want is for air to be able to bypass the piston in one direction optimally. when you fill the chamber the air needs to have to try to get past the piston some what because that is what pushes the piston against the barrel to achieve the initial seal. However you don't want to much air going past in the other direction because it takes to much pilot air speed to pull it off the barrel to get it to fire. I use one way valves in my pistons, but many will say that they are unnecessary, just my preference. I hope this all works out for you. I think you will find that if your piston valve works out well that it trumps all of your other valves easily. Good luck. Lock
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