SpudFiles

I have some misc spare parts (fully threaded brass tube, pipe nipple, 1/2" > 1/8" reducer, schrader) and was thinking about piecing together a small caliper BB cannon from them.

I was wondering if this design for a valve would work or would the suction from the barrel not allow the valve to open long enough or fast enough? I realize if it did work loading the barrel would be tricky.

This is a generic coaxial design. Of course it will work. I would put a blowgun where the schrader is and put a 1/4'' schrader adapter in the end of the blow gun without the core. It's easy to fill and gets better flow. You would have to hold it open to fill it and shut it before you remove the air supply.

If you're gonna steal a JSR design, put the blowgun in the right direction

Crap! Let me edit that. I didn't re-save the pic. Although the blowgun will work either way.

It would work, but only at low pressure. When the valve is installed the correct way, air forces it closed. When it is backwards, air forces it open, only against the tension of the spring, which is not very strong. And the blowgun is more ergonomic when installed the correct way in this instance.

I was wondering if this design for a valve would work or would the suction from the barrel not allow the valve to open long enough or fast enough?

There is no suction in a piston valve.

I realize if it did work loading the barrel would be tricky.

Difficult loading comes with any coax

See the Mouse Musket in my sig for a functional build of that basic design. Yes it works. The hard part is the build quality so the piston does not leak too much and does not have too much blow by between the pilot area and the chamber area.

Three common problems people have are

The piston won't seal on the barrel due to surface imperfections preventing an air tight seal,

The piston has too much leakage past it so opening the pilot valve (blowgun) the air escapes out the pilot instead of moving the piston,

the piston fits too tight so it doesn't fire. Use care and make sure the piston barrel seal is good and the piston has very little leakage past it, and it moves freely without sticking.

Use a bumper so when it does pop open, it does not hammer it's way out the back.

I put it together and as previously posted there wasn't enough pilot flow with schrader, when I removed the core it worked great so a blowgun design might be good... Right now the piston is just a perfect tight fit and I have the pilot area lubed up, I used dremel to make a groove in piston for barrel seat, it seals excellent.

sco77 wrote:there wasn't enough pilot flow with schrader

the piston is just a perfect tight fit

I could pilot a 2" valve with a schrader...