Air Cannon Help

Build a homemade water gun or water balloon launcher and tell us about it.
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Finnster
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Air Cannon Help

Post by Finnster » Mon Jun 08, 2009 1:53 am

Well, I've got an air cannon that was designed for JSPB (a foam combat sport similar to Nerf), and I would really like to convert it to a water gun. The first picture is it's (almost) current state and the second is what I'm planning on doing to it. Any suggestions?

Image

Image

Thanks
-Finn

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Drenchenator
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Re: Air Cannon Help

Post by Drenchenator » Mon Jun 08, 2009 2:22 am

Welcome to Super Soaker Central, Finnster!

I'm afraid your design will not work. While converting a water gun into an air gun is often possible, converting an air gun to a water gun is not. Simply put, a container full of water can't just simply be attached to a pressure chamber; orientation and flow direction must be taken into account.

To illustrate, water falls and air rises. Most air pressure water guns (like our very own APH homemade water gun) have a separate pressure chamber that uses this principle. In your gun, air will just flow out the nozzle; no water will leave. The water must be pushed out, and the pressurized air must do the pushing. In your rebuild, the air only pushes the water back into the water backpack, and should the backpack be unrated for pressure, it would burst--not a good thing to happen. This is why the air must be above the water: it has to push the water out.

In short, if you have some experience with building air guns, you will be much happier making a new water gun from scratch than from retrofitting an air gun, which would only yield poor or no results.

For further reading, I suggest this excellent article by Silence entitled How water guns work; it's a thorough introduction to the principles behind common water gun designs.
The Drenchenator, also known as Lt. Col. Drench.

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Finnster
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Re: Air Cannon Help

Post by Finnster » Mon Jun 08, 2009 7:35 pm

Drenchenator wrote:Welcome to Super Soaker Central, Finnster!

I'm afraid your design will not work. While converting a water gun into an air gun is often possible, converting an air gun to a water gun is not. Simply put, a container full of water can't just simply be attached to a pressure chamber; orientation and flow direction must be taken into account.

To illustrate, water falls and air rises. Most air pressure water guns (like our very own APH homemade water gun) have a separate pressure chamber that uses this principle. In your gun, air will just flow out the nozzle; no water will leave. The water must be pushed out, and the pressurized air must do the pushing. In your rebuild, the air only pushes the water back into the water backpack, and should the backpack be unrated for pressure, it would burst--not a good thing to happen. This is why the air must be above the water: it has to push the water out.

I added check valves in the rebuild so the air and water couldn't go back into the backpack or tank.

Finn

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Silence
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Re: Air Cannon Help

Post by Silence » Mon Jun 08, 2009 7:38 pm

You still need a "pressure chamber," or a tank in which water and pressurized air is stored. Right now, the air will push through that middle compartment and then just shoot out the nozzle. Because there's more pressure in the middle compartment than in the backpack, it won't let any more water out.

Also, what are you using to pressurize the air?

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Finnster
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Re: Air Cannon Help

Post by Finnster » Mon Jun 08, 2009 7:56 pm

Silence wrote:Also, what are you using to pressurize the air?
Bicycle pump, I kind of see what you guys are saying now. I guess I'll just build another one and leave this one for its intended uses.

Finn

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Drenchenator
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Re: Air Cannon Help

Post by Drenchenator » Mon Jun 08, 2009 8:05 pm

Perhaps I wasn't completely clear. The water needs to be close to the nozzle so that the air, on the other side of the water, pushes out the water.

The current configuration you have will not even allow water through the nozzle, because the pressure on the out side of the check valve is greater than the pressure on the in side. The water will not simply flow in if it has insufficient pressure to flow. The water must be pushed out and must be pressurized somehow. The air chamber, in your current configuration, does nothing to pressurize that water.

I made a diagram to show a water gun that can be made using an air pressure chamber; but bear in mind that other designs, made completely from scratch, would perform much better and would be worth your while more.

Image

In this design, you can attach your air pressure chamber to a water pressure chamber with a check valve. When there is no pressure, you can fill the water chamber with water using the water fill valve (a ball valve) at the top. Closing it, you can then pressurize the air tank through its fill. Valve. At this point, the gun is ready to use.

In this design--as in all air pressure designs--the nozzle is connected to the bottom of the water tank. Why? Gravity. The water stays at the bottom of the tank, so to be pushed out of the tank by the pressurized air, it must flow out the bottom. Should you try to attach the nozzle above the water, like at the water fill valve, no water will leave when you open the valve; instead, all your pressurized air will. The water isn't just going to jump up and flow out. It has to be pushed out by the air pressure, and if the air pressure doesn't need to push it out, it won't.

Edit: Didn't notice your previous post before posting this. Good luck with the other build if you aren't good to go down this road.
The Drenchenator, also known as Lt. Col. Drench.

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Finnster
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Re: Air Cannon Help

Post by Finnster » Tue Jun 09, 2009 1:52 am

Well, I've been thinking about a whole new kind of water gun, well, I should say one that I've never built before. I'm thinking about building a bladder type gun, like the super CPS, I've drawn a picture (still not great with MS Paint). This one should work, right?

Image

Finn

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Silence
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Re: Air Cannon Help

Post by Silence » Tue Jun 09, 2009 2:40 am

Yes, that's perfect! The article can obviously fill in the details, but you have the general idea. :cool:

I'm glad you're taking the time to work through designs on your own. Many people end up following the tutorials to the letter, and the end result is just like every other APH out there. Rearranging, resizing, and otherwise changing components is great (provided everything still works).

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