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Metal barrel sealing piston valve(need some advice)

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Metal barrel sealing piston valve(need some advice)

Unread postAuthor: Fnord » Thu Jun 14, 2007 9:09 pm

I'm working on a metal barrel-sealing piston valve, but I can get it to seal worth crap. It has a fairly standard pvc piston, just in a 2" steel housing. I cant get the neoprene rubber face to seal against a 1" steel pipe no matter what I do.
I wanted to know if anyone has made a similar piston before and what you did to get it to seal properly.
This is really frustrating.
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Unread postAuthor: VH_man » Thu Jun 14, 2007 9:31 pm

are you sure the steel pipe is nice n' smooth? i know steel pipe isnt that great in the smoothness category. try taking a buffer to it and making the sealing part of the pipe shiny enough to see your face in........

other than that, i have no clue what the problem is.
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Unread postAuthor: Kenny_McCormic » Sun Jun 17, 2007 12:49 pm

unsquare cut to the pipe?
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Unread postAuthor: Fnord » Sun Jun 17, 2007 3:50 pm

The pipe is cut perfectly square.
I just got some metal sealer (used to seal gaskets) So I'm going to experiment with that.
I'm also going to polish the pipe more.
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Unread postAuthor: Velocity » Sun Jun 17, 2007 4:53 pm

I have made a piston valve with only welded steel pipe; the kind that is rough on the inside and has a big metal seam going down the length of it. It wasn't ideal, but I got it to work with almost no trouble. I didn't polish it either. I am thinking that your piston might be too big. A piston that fits snugly in a PVC seat will work fine, because the PVC seat is smooth and a little bit of grease makes it move fine. However, a piston that fits snugly in a metal pipe seat sometimes doesn't work fine. Air can escape through the little channels between the piston and the pipe (the uneven surface), and therefore it would actually work better if it was loose.

A good idea is to wrap a layer or two of duct tape on the piston seat. It will make it smoother. I did this on my launcher, and it worked like a charm.

EDIT: spudthug, its possible that his piston is getting caught up on the piston seat somewhere, so this suggestion was meant to remedy that.

Anyways, another thing that you can do is glue a circle of neoprene on the barrel port. If the piston doesn't seal after that, I don't know whats wrong. Like spudthug says below, a rubber on rubber seal should work well. I prefer the high grade neoprene that is sold in 1/8" sheets to a rubber coupling, because it is easier to work with and probably a higher quality material too. Thats just my opinion though.
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Last edited by Velocity on Sun Jun 17, 2007 5:30 pm, edited 1 time in total.
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Unread postAuthor: spudthug » Sun Jun 17, 2007 5:24 pm

rmich his problem isnt getting it to move, it just wont seal..

fnord i had the same problem.. i tried everything but it turned out the my nipple wasnt in straight and i had already jbwelded it so i took it to my dad and he said we would square it in the lathe...we squared it and now it works realy good...

since u said it is in straight maybe u should put one of those rubber couplers off the edge of it jsut a tiny bit to make it a rubber on rubber seal..

or make the face bigger somehow
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