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Compact piston

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Compact piston

Unread postAuthor: metalmeltr » Thu Apr 07, 2011 4:21 pm

I just had an idea for a compact piston for coaxial cannons that would ride inside the barrel. The sealing face would be attached behind this piston and seal gently against the chamber walls to facilitate valve actuation. Im not sure if it will work but it would be able to reduce pilot volumes by having less area behind the piston. Flow would be slightly reduced. I envision this piston being made of two half lapped pieces of plexiglass epoxied together. Custom plugs for the chamber could also reduce pilot volume.
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valve.jpg
Green-barrel
Blue -chamber
Black piston
red-seal
valveii.jpg

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Unread postAuthor: Gaderelguitarist » Thu Apr 07, 2011 9:02 pm

You could even go so far as to shape the mating edges of the cross piece and the sealing face to an arc to reduce turbulence and help guide the air out the barrel.

Looks interesting, Though I would probably put rubber on the barrel and have the piston made from aluminum or some impact resistant plastic.
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Unread postAuthor: metalmeltr » Thu Apr 07, 2011 9:34 pm

Thats a good idea, Do you think silicone could be applied to the back of the barrel to make it work?
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Unread postAuthor: Gaderelguitarist » Thu Apr 07, 2011 9:46 pm

Silicone would work I believe as long as it's applied evenly. Sheet rubber or an o-ring would be your best bet since that would mean simply making your barrel squarely cut.
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Unread postAuthor: metalmeltr » Thu Apr 07, 2011 9:51 pm

Once again im thinking about doing things the hard way, if i could find an o-ring and just glue it carefully to the back of the barrel.
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Unread postAuthor: ilovefire » Thu Apr 07, 2011 9:59 pm

you aslo have to remember that a lot of pressure will be on that Oring and just glueing it to the barrel wont work
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why make it if it dosent shoot?
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Unread postAuthor: Technician1002 » Thu Apr 07, 2011 10:02 pm

Look at my Mouse Musket for a way to attach an O Ring to the end of a barrel so it doesn't get blown out the barrel. I tested mine to a little over 100 PSI and it held fine.

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Unread postAuthor: metalmeltr » Thu Apr 07, 2011 10:10 pm

How wolud you sugest tackling this problem? I think that some super glue carfully applied to enable the sealing face of the o-ring to remain flexible should be sufficient

Edit: looks like tech answered my question before it was asked
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Last edited by metalmeltr on Thu Apr 07, 2011 10:15 pm, edited 1 time in total.

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Unread postAuthor: ilovefire » Thu Apr 07, 2011 10:14 pm

metalmeltr wrote:How wolud you sugest tackling this problem? I think that some super glue carfully applied to enable the sealing face of the o-ring to remain flexible should be sufficient


i am sure it would work perfectly fine, just not past like 5psi, maybe 10 if your lucky
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Unread postAuthor: Technician1002 » Thu Apr 07, 2011 10:20 pm

To keep my o ring from blowing out the outside of the barrel is grooved to hold the ring. Then the coupler holds it inside the groove. To prevent air behind the ring blowing it out, the space was filled with caulk, then the ring was squished into position. It is clamped in a groove and glued with caulk. Only the very edge of the o ring protrudes past the end of the barrel for the seal.
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Unread postAuthor: metalmeltr » Thu Apr 07, 2011 10:34 pm

Ok that sounds very much like a PVC union and that is the exact way i held th o-ring on that to keep it in place.
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valve III.jpg
Blue is the one piece piston
Black is the o-ring

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Unread postAuthor: Technician1002 » Thu Apr 07, 2011 11:32 pm

That is a wide ratio piston (large OD to Seat). The problem with them is as the pilot pressure drops the large area opens the pressure while the pilot is at a relatively high pressure. When the chamber begins to vent out the barrel and the chamber drops a little, the pilot pressure will slam it back closed.

The only way to keep one of the wide ratio pistons open is to use a large pilot valve. Otherwise they honk.
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Unread postAuthor: Gaderelguitarist » Thu Apr 07, 2011 11:34 pm

Now all you have to work out is the bumper, and of course ensuring that the thin piston won't deform with the abuse it will receive. Not too difficult.
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Unread postAuthor: metalmeltr » Fri Apr 08, 2011 10:03 am

The piston does not nesasarily have to be a wide ratio. This is only the way i drew it. These sizes have no reflection on actual pipes.
What do you think about bouncy ball bumpers? Cut in half and glued to the plug. Would the ball bounce the pistion back into the closed position?
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Unread postAuthor: jackssmirkingrevenge » Fri Apr 08, 2011 10:28 am

What's wrong with a cup type piston as illustrated here?

It can be just as compact and avoids the awkward shape running in the barrel.
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