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Building a CO2 water cannon without a tank?

Posted: Mon Sep 07, 2009 12:00 am
by thaigringo
Hi guys,

quick question...

I go to Thailand every year for the worlds biggest water fight (see ... terfights/ ), and I am trying to put together a killer watergun.

The concept needs to be ultraportable, powerful, tankless and pumpless.

Through reading, i've kind of gotten the idea that this can be done, but I didnt see any build plans for a gun that uses CO2 to draw a stream from a pool of standing water through a venturi, and pressurize it out of a nozzle, instead of just using Co2 to build up pressure in a tank.

The concept in my head works the same as an off-the-shelf power washer, but replacing the electrical pump with a Co2 source to build pressure.

During songkran, there's tons of 50 gallon buckets all over the road full of water for people to refill their water guns. I'd like to just be able to stick a 6 foot hose inside of it, blast away, than run down the street and do it again at a different water source.

Can anyone suggest a built plan for such an ultimate weapon, or any other suggestions on something that would work for a citywide water war? Everyone else in town uses supersoakers and dipsticks, and i'd really like to see a bit more technology on my side this year for the carnage.

Can this be done?

Thanks in advance everyone, happy hunting!

-Toby V.

Re: Building a CO2 water cannon without a tank?

Posted: Mon Sep 07, 2009 1:37 am
by SSCBen
Welcome to SSC!

From my understanding of how a venturi pump (which is what I assume you mean by "venturi") works the CO2 would be in the stream during firing. That should seriously harm range. Otherwise it sounds valid, though I'm not quite sure how much water flow you will generate this way and I don't know the best way to find out as it is a two-phase flow.

A novel idea you might like is a water gun that requires one stroke to fill a chamber (which shouldn't be very difficult) but then uses CO2 or another gas to fire that chamber. With the right pneumatic logic (which I already am familiar with from some other projects of mine) you should be able to modify the mentioned design to operate completely automatically. I find this idea to be rather interesting--I'll investigate. Thanks for sparking some creative thinking in me. :)

Re: Building a CO2 water cannon without a tank?

Posted: Mon Sep 07, 2009 1:49 am
by thaigringo
Thanks for the reply and the ideas! During Songkran, everything is pretty close range, and more for partying, soaking and getting soaked.

Check out this vid link,

Check out the cannon that the guy is using at the 40 second timestamp, could you do something like that with small hot tub pump and a portable gas-powered pump (like the ones used in gas operated compressors), and just stick a suction hose in a reservoir?

Maybe a sump pump?


Re: Building a CO2 water cannon without a tank?

Posted: Thu Sep 10, 2009 3:00 am
by SSCBen
I'm afraid I only see people with buckets at 40 seconds. If you mean the guy at 37 seconds, it depends.

Generally I suggest avoiding electronics and water. The power requirements are pretty high and unless you use high capacity batteries you shouldn't expect much from them. Not to mention that water and electronics can go very bad. Also, the only pumps I've seen that are adequate for our purposes are fairly expensive. Electrical pumps, when done correctly, can do what you want, however.

Gasoline powered pumps do work well, however, they are expensive, require expensive fuel, and are fairly loud.

Sump pumps are low flow devices from what I know. I'll admit I don't know and don't have time to do the research.

In similar news, I finished a preliminary design of the water gun I thought of. Here's the basic setup of the water gun:


I'm not going to explain the symbols so Google for "pneumatic symbols" or something to that effect if you're confused. Clippard's catalog also has many of these.

The air cylinder pushes a piston which in turn pushes water out of a nozzle.

The cycle is broken into two main parts, the first of which has two parts as well:

Filling: (1) The trigger is not depressed (the DCV on the left is the trigger valve). High pressure gas flows from the right of the air cylinder to the left such that the air cylinder retracts, pulling water into the water chamber (water chamber and associated water valves not shown). The two chambers eventually equalize. Getting a full stroke requires exhausting the right chamber... so... (2) the needle valve should provide the right timing such that the air pilot valve exhausts the right chamber when necessary.

Firing: The trigger is depressed. The left side of the cylinder exhausts and the right size is pressurized, which in turn pressurizes the water and the stream is shot.

Not too complicated is it? Maybe it is.

Further modification of the design might be necessary if the air cylinder doesn't exhaust quickly enough. Small QEVs will solve this problem.

This water gun has a number of advantages over other designs, namely...
- No pumping
- Water can be stored in a non-pressurized tank
- Gas use is more efficient than other piston designs as still pressurized gas left in the chamber is recycled for the filling stage
- The only limits on performance are budget
- No plastic pipe is under gas pressure

The biggest disadvantages of course are the relative complexity of the circuit, the cost, the potentially difficulty getting these parts used, and the check valve that must go in the water nozzle assembly. So it's NOT an ideal design by any standard, but I find this possibility to be very intriguing.