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"Power Tube" Coaxial Cannon Concept

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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"Power Tube" Coaxial Cannon Concept

Unread postAuthor: BR01 » Thu May 24, 2018 9:55 pm

Hello all, been a lurker here for well over a decade, but here's my first original concept. When I say original though, I mean I just haven't seen it before. Anyway, here's a model I threw together of a coaxial cannon concept.

The idea is to have the piston connected to a threaded rod in a tube that controls the filling and firing cycle. It will be filled and fired the same way, filled through a hole in the end plug (red) and backpressure released to initiate the firing cycle.

The barrel seal itself is a rubber stopper (black) drilled through for the threaded rod. As pressure is applied through the rear of the tube, the floating piston (orange) pushes the whole assembly forward until it is past the holes in the power tube (white). Note that the floating piston is free to move axially along the threaded rod. The spring would be compressed slightly at that point to ensure there is forward pressure on the stopper keeping it in the barrel (green) before the chamber pressure takes over that job.

Fill Position:
Image

When filling is complete and pressure stops increasing, the floating piston would be pushed back by the spring to seal the chamber from the power tube. Once the backpressure is released, air pressure from the front of the tube would push the floating piston and the entire assembly towards the rear of the cannon, allowing air to flow down the barrel.

Fire Position:
Image

That's the idea, anyway. Any concerns before I start building it this weekend? Suggested changes?
Thanks for your time.
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Re: "Power Tube" Coaxial Cannon Concept

Unread postAuthor: jakethebeast » Fri Jun 01, 2018 3:00 am

I believe this will not work, as the pressure around the pilot tube thingy will keep the valve shut. I have tested this similar idea with a barrel sealing piston valve snd it also failed to work
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Re: "Power Tube" Coaxial Cannon Concept

Unread postAuthor: mrfoo » Fri Jun 01, 2018 7:09 am

As long as you can seal around your "threaded rod" (hint - don't use a threaded rod), your "fill" sequence will work nicely. I like that.

The firing sequence won't happen unless your barrel diameter is smaller than your floating "fill" valve - as drawn, the pressure exerted on the barrel sealing valve will be higher than that on the floating valve.

You might be able to get away with it by having mechanical actuation on the "stem", to "crack" the barrel sealer open - effectively making an unbalanced QDV - if you're doing that, make the barrel sealing valve a o-ringed, and you can do away with the need for a floating "fill" piston at all. You might end up with something that looks a bit like BtB's CBHV (if you squint a bit and look at it from an acute angle with a lot of the lights turned off).

I have an idea for one of these I've been meaning to make for a while, actually. Must make myself some lathe time.
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