SpudFiles

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.

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.

Thats a good idea, Do you think silicone could be applied to the back of the barrel to make it work?

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.

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.

you aslo have to remember that a lot of pressure will be on that Oring and just glueing it to the barrel wont work

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.

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

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

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.

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.

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.

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.

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?

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.