Quick Exhaust Assembly

[DReynolds]

I've decided to build a cannon with a piston release. I understand the whole concept very well, but my only concern is the exact construction of my piston. For my first cannon, I'd much rather have a definite design to work off of before I go trying to invent new things. Does anyone know of a site with detailed plans as to how exactly to construct it? There are plenty of sites that say theyir guns use it, but finding one with and instruction-type section has proved impossible.

[chewy]

I dont think you will find plans with exact measurements. There is a great varryation in tolerances between manufactures and even between lots of pipe. I know there are several on the net, but i have lost my list. Will this be a coaxial or over under?

[DReynolds]

Originally the plan was a mini coaxial essentially just to house the piston with two exterior tanks to hold air and act as a base, but for my first, I decided to keep it simple, so it's just coaxial now. It's now actually built, but I'm still tweaking. It seems that I pushed my barrel too far down, and now the piston may be too long, so I'll have to make a new one. My other issue at this point is that the threads between the female adapter and the cap are not airtight at any pressures. It seems that the only solution will be gluing it permanently, but is that the inevitable conclusion? I'd like to maintain access to the inner chamber for tweaking,cleaning, etc. Any ideas?

[DReynolds]

By the way, in case you were interested, this is the final design of the piston. I used 4" pipe for the chamber, so the piston consists of two 3" endcaps connected by a small length of 3" pipe. I had to Dremmel the end caps down to fit inside the chamber, but they're nearly airtight now. Now here's the part I'm proud of. Imagine the whole cannon standing so the barrel is up, with the piston inside. The part of the piston that's down right now will be called the down-side and the side above, the up-side. On the down-side, I've drilled a hole and tapped in a check valve. On the up-side, I've drilled a second hole to one side of where it presses against the barrel. The purpose of a check valve is that it allows air to pass through, but holds a certain amount of pressure behind it. Say it hold 10psi back, if you pump it with 50psi, it allows that p[ressure through, but holds at least 10 pounds greater behind than in front of it. Here's how it comes in handy. It's installed inside the piston, and when you pump, it allows air through, but keeps enough pressure behind it to push it up against the barrel. The rest of the pressure pushed past it and through the second hole into the chamber. For additional air-tightness, I cut two grooves in the 3" pipe and put for neoprene rings around it. These ensure that the piston is truly sealing the chamber.
That's a fairly exhaustive description of the whole assembly, hope it makes sense to anyone who cares to read.

[chewy]

I admit i am lost with the explanation. With the treads , have you tried cleaning up the excess flashing or plastic left from the mold? Plumbers compound or Teflon tape can go a long way in sealing leaks. Be careful not to over tighten as this cuts down a lot of friction and you can split you female coupling. ntp threads are a tapered thread and act like a wedge.

[DReynolds]

Been a little while. It's all completed and working better than expected. We found that tape works well to seal it, but may also try liquid plumber's seal which is a bit messy but should do the trick. As I mentioned, it's actually working better than expected. I don't have to disassemble and reset the piston ech time - it just gets pushed right back, and talk about silent but deadly. This thing is so quiet but seems to pack more punch than anything else in my collection. I have digital pictures of it, if you're interested in a more visual explanation. Is there a way to post them on this forum?

[tatorassassinator]

Hey reynolds send me some pics

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