Coaxial Piston Cannon Troubleshooting (no air pressure)

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Rocky44hunt
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Tue Oct 20, 2020 9:11 pm

Hello - I recently set out to build "my son" this cannon:



Well, now I can't get it to hold air it seems:



I followed all of the steps in the Nighthawk video with the following mods:

- I used a CPVC connector with a 1/2" nut on the end to connect the ball valve to the nipple. I couldn't find a threaded ball valve that would screw onto the nipple used in the video.
- I have an extra reducer in my series of reducers from 3" > 1/2" because I bought the wrong size originally and cemented it before realizing it
- I used a piece of vinyl floring instead of rubber inside the piston.

I'm looking for some help for why I'm unable to get air to pressurize. I've posted some still pics below of the kit dismantled where it's not cemented. If the answer is "start over", how the world can I dismantle this thing, or do I need to buy all new parts?
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jackssmirkingrevenge
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Wed Oct 21, 2020 6:45 am

Welcome to the forum, and nice 'stache.
Rocky44hunt wrote:
Tue Oct 20, 2020 9:11 pm
"my son"
:roll: :D

I think the piston is probably the issue, especially if you are using a hand pump.

If it is not free to move and reasonably air tight, then air will just go past it as you are filling and go straight out the barrel.

If you were filling with a compressor it would probably work.

One solution would be to put a suitably sized spring between the fill coupling and the piston to make sure it is butted up against the barrel when you start filling.

The spring would also help mitigate the impact from the piston while firing.
hectmarr wrote:You have to make many weapons, because this field is long and short life
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Labtecpower
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Wed Oct 28, 2020 1:33 pm

I would try to find something like a PVC end cap or tin can with a reasonably tight fit in the piston housing, and use a piece of reasonably soft rubber as a sealing face. If the piston is too loose in the housing the most simple solution is wrapping electrical tape on the front and back of the piston until it is snug. Try not to wrinkle it though, and service life will not be endless.
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jackssmirkingrevenge
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Thu Oct 29, 2020 6:29 am

Labtecpower wrote:
Wed Oct 28, 2020 1:33 pm
If the piston is too loose in the housing the most simple solution is wrapping electrical tape on the front and back of the piston until it is snug.
Lest we forget, there is also the possibility of casting epoxy pistons ;)
hectmarr wrote:You have to make many weapons, because this field is long and short life
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