SpudFiles

Ok, I plan to build a coaxial piston valve cannon, chamber will be 4 foot long and 4" of diameter. My barrel will be 6 foot long and 2" of diameter.

My piston will be a 3" coupler.

how many inch should I leave behind the piston ?

thank you

I believe it's the same as the diameter of the barrel, in your case about 2 inches. You might need an extra inch if you want a spring in it.

2 and a half inches is the most common gap

You only acctualy need 1/2 the barrel diameter of piston momvent (1" in your case) to allow full flow. Not very much harm will occur from making it oversize, though, so you might go with 1.5" or 2".

ok thank you,

I tought about a new way of making a piston, tell me what you think about it

Normal piston :




My simple and light piston :

It should work, but I think it'd be simpler to just epoxy the rubber to the face of the coupler. Might work better too.

Anyway, have you considered filling the empty side of your coupler with some "great stuff" or similar expanding-foam insulation? Such action would decrease the pilot volume, improving preformance.

boilingleadbath wrote:It should work, but I think it'd be simpler to just epoxy the rubber to the face of the coupler. Might work better too.

Anyway, have you considered filling the empty side of your coupler with some "great stuff" or similar expanding-foam insulation? Such action would decrease the pilot volume, improving preformance.

I operate my cannon with a sprinkler valve .. I think it wont change nothing. And Is that foam hard ? cause If not, the foam will get smashed in the piston due to the pressure. And If I put something harder, it will probably be heavier.

I was just wonering how much room is there from a 3" coupler in a 4" pipe.Is it veyr small or quite a gap?