I stumbled upon a website last night, after Googling for water cannon.
Seems that <a href="http://www.sscentral.org/">SS Central</a> is a forum where mebers discuss how to modify Super Soakers, for increased performance.
There's a lot of info on these modifications, but the post that caught my attention was: <a href="http://www.sscentral.org/tech/homemades/aph.php">The Air Pressure Homemade</a> , by Doom
I thoroughly enjoyed reading the entire article. Now, although there is a disclaimer:
<b>All content on SSCentral.org is Copyright Ã‚Â© 2001-2004, the Super Soaker Central project, unless otherwise stated. All rights reserved</b>...
The article stated ( quoted from <b>Construction</b> ):
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The design is 100% customizeable.
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I'll admit; I'm pretty lazy!- Although the design has an onboard pressurization system (homemdae pump, using 1/2" check valves), I think that the design would be more compact (as well as a lot easier) if you were to simply add a schrader valve:
Pressurization could then be accomplished via a simple bicycle pump.
Now, before anyone has a cow, I relaize that the design utilizes DWV Bell Recucers. Personally, I would feel comfortable pressurizing this particular design between 50-70psi max. But that's me, not you.
I take no responsibility whatsoever if you get silly, and try to overpressurize this type of design. And I would highly recommend that the Bell Reducers be swapped out for pressure-rated 3" Couplings.
And seeing as how most 3" PVC pipe is pressure rated at 260psi, can you even begin to imagine the stream of water that would blast out of this thing, if you were to add a 3/4" BRASS Ball Valve, and an onboard CO2 system? -Definitely overkill, and I would not recommended pointing at anyone, but it would be pretty powerful for non-living targets!
As a side note;
I give full credit for this design to "Doom", from the SS Central Forums.
And I have <b>not</b> built, or tested one of these yet. I'm merely passing along a great idea.