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First Piston Valve help

A place to ask general spud cannon related questions.
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First Piston Valve help

Unread postAuthor: SpudStuff » Mon May 15, 2006 6:53 pm

I am currently trying to build a barrel sealing piston valve for a mini pnumatic. My problem is that the air leaks out of the barrel most of the time. and when it does seal the blo gun does nothing but let the air out. the seal on the pistion is thick rubber from a downhill bike inner tube. the rubber is very soft and has worked in a previous coaxial cannon. the valve body as a 3/4 x 3/4 x 1/2 inch Tee
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Unread postAuthor: jrrdw » Mon May 15, 2006 7:01 pm

I don't see a pilot valve hole in your piston, plus the piston should be a cup shape, so as to seal off the release chamber thats behind the piston, that way all the air don't leak out when you pull the trigger, thats what it looks like to me.
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Unread postAuthor: Jakal444 » Mon May 15, 2006 7:14 pm

Sweet piston, small and compact! If you could provide a little bit more detail on the construction details that would be great (you know the barrel-tee interface and such).

What pressure does it leak at?

Like jrrdw said, its the cup that makes a good seal, however it seems that your barrel and piston are roughly the same diameter so Rather than a cup make it so that it protudes into the barrel and seals.
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Unread postAuthor: SpudStuff » Mon May 15, 2006 7:22 pm

Do you mean like this?
other wise what else do i need
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Unread postAuthor: sgort87 » Mon May 15, 2006 7:41 pm

I think he means it should be more like this. (which it should for better sealing performance.) The cupped piston will move just a bit more to the left as it locks onto the barrel. The piston will actually be slightly inside the barrel.
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Unread postAuthor: Jakal444 » Mon May 15, 2006 8:20 pm

Thanks Spudstuff I am definately going to make this, and thanks sgort thats exactly what I meant!

I would like to see this gun complete now so be sure to post some good pictures.
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Unread postAuthor: SpudStuff » Mon May 15, 2006 10:06 pm

dont tHAT DOSEN'T WORK
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Unread postAuthor: sgort87 » Mon May 15, 2006 11:49 pm

Huh? The cupped piston thing works for me.
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Unread postAuthor: Jakal444 » Tue May 16, 2006 1:57 am

Why doesn't it work? If anything it should work better (if you get the shape right).
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Unread postAuthor: Benny » Tue May 16, 2006 6:15 am

will the blowgun exaust a pilot that sise?
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Unread postAuthor: jrrdw » Tue May 16, 2006 7:24 am

When i say cup, i mean the inside of the end cap, should only be in the tee far enough to block off the air chamber, the barrel has to be in the middle of the tee. Then the end cap creates the relief chamber that the blow gun is attached to, but still enough room for air chamber to vent into the barrel once you pull the trigger/vent the relief chamber. There is a more detailed drawing of what i'm talking about in spudwiki, under the piston valve link.
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Unread postAuthor: sgort87 » Tue May 16, 2006 9:05 pm

Okay, okay. I left out the tee. Geez. Sorry.
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