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# Water Machine Gun

Shoots 'Bullets' of Water
 (+5) [vote for, against]

First off, not ice.

I imagine this would be purty hard to pull off without some sort of battery power, so I'm putting that as a given.

The way it woiks is this: you pump it up, like a regular water blaster, but instead of a stream of water, which only goes ever so far, it shoots water 'bullets'. It accomplishes this by shooting a lightning-fast alternation between water and air. This could be done using some kind of turbine in the first part of the output tube which turns a rotary valve. This valve is hooked up to the water and air supplies, so that when the it is in one position, it lets air out; when in the other position, water. This is the basic key to the alternation.

Secondly, because you're shooting out air just as fast as the water, you'll need more air. This is where the batteries come in. They power a pump which maintains a constant pressure inside the air reservoir, which will probably need to be somewhat larger than the reservoirs on regular blasters.

Now, the advantage of shooting 'bullets' of water is what?

See, a while back, we were shooting water at one another, and I noticed that when the water tank was just empty, the blaster shot 'bullets' in the manner described above. They went further than the stream did, although the air pressure was now much lower. Then it hit me: the speed of the water stream, and thus its distance, is limited somewhat by the density and viscosity of the water. (Imagine trying to squirt honey. Just like that, only less so.)

The solution is to put pockets of air between chunks of water, so that instead of shooting a 'string' of water, you're firing relatively tiny pieces of it. And they go further.

Oh, and it also looks very cool.

I see the valve as being the weakest link in the design, and I'm open to suggestions. For example, it may be better to power the valve by battery. And perhaps someone could think of a better category? Like Sport: Projectile or Sport: Water or Product: Toy? I couldn't think which was best.

 — galukalock, Jan 02 2004

How Water Blasters Work http://entertainmen.../water-blaster3.htm

Bob Long Paintball Guns http://www.boblong....ewsite/bobmain.html
Most are capable of automatic operation of 25 bps (balls per second?) [xrayTed, Oct 05 2004, last modified Oct 17 2004]

Baked http://www.i-mocker...er-guns/default.php
[notmarkflynn, Feb 16 2006]

This type of irrigation sprinkler can emit short bursts of water. A simple redesign should allow all the bursts to travel in the same direction for watergun purposes. [Vernon, Aug 27 2011]

 Sort of like a pulsing super soaker. They can do it without batteries for showers so it doesn't sound at all difficult.

Your explanation of why the water "bullets" went further doesn't fly, however. If the water tank was nearly empty, the available air pressure is higher (more space to hold the air, so each cc of water spurting from the gun will lower the air pressure by less, or something).
 — DrCurry, Jan 02 2004

The way most standard water blasters, including mine, work is this (see link): there are two reservoirs, one for the water (the tank), and one to pressurize the water. The second has air in it already, but you pump water into it from the first. This raises the pressure inside res #2 dramatically. When you pull the trigger, the pressure forces the water out through the bottom of res #2, through the tube, and out the nozzle. As the water flows out, the pressure in res #2 decreases, until, when nearly empty, the pressure is nearly identical to ambient pressure.
 — galukalock, Jan 02 2004

 I was assuming you kept pumping between water refills (my recollection being that the air pressure generally runs down before the water runs out).

But given the design change shown on your diagram (my experience with Super Soakers is a few years out of date), my comments are even more the case: water not being compressible, you can obviously achieve much steadier high air pressures when there is only a little water left in the gun.
 — DrCurry, Jan 02 2004

 Apparently we're having a misunderstanding here. Let me restate the situation in more detail. Feel free also to try it out on one.

 The water *tank* was just empty, as I had just pumped the very last of it into the *pressure* res. Since the pressure meter (yes, mine has a pressure meter) read fairly low, I pumped it up a little. The trouble with doing this is that you're pumping a compressible fluid (air) with a fairly small pumping cylinder designed for pumping noncompressible water, so you must pump many more times to achieve any reasonable pressure.

 Anywho, I pulled the trigger and sprayed the rest of it. As it was finished with most of the water, the last drops were dripping down the inside of the (translucent) pressure reservoir. These flew out much farther than the stream did, although by now, as you say, the air pressure was lower than it had been when full, since most of the material was gone. I have reproduced this effect numerous times throughout the summer and autumn; that's the reason I remember it so well.

I really don't know for absolutely sure *why* it does that; I have taken a shot at explaining it. All I know is it does, and I aim to use the same principles to shoot a rapid-fire series of water 'bullets' in the same manner.
 — galukalock, Jan 02 2004

 If the water tank was mostly empty, when you pull the trigger mostly air would escape. Air, being much lighter than water, would travel much faster. As the remaining few drops of water drip down the inside of the pressure reservoir, they enter the high-speed stream of air and are 'spit' out at the observed higher rate of speed. This would be my explanation.

What your idea wants is not alternating water-air, but water 'bullets' being accelerated by a high pressure blast of air, more like a paint-ball gun.
 — xrayTed, Jan 02 2004

gl: you have to pump "many more times" because you're compressing a larger volume of air (although it is also possible the valve system is breaking down due to the lack of water in the system). But the effort needed to compress a given amount of air is not going to change whether you're pumping water or air. Do the math.
 — DrCurry, Jan 02 2004

 Another thing [glock] could do to improve distance would be to mix some polyox with his water. The polymer keeps the water coherent and less prone to falling apart as it flies. This is done with those tricky computerized fountains as well as firefighting with high buildings.

 I wonder if you could substitute corn starch for polyox? It is a non-newtonian fluid also, and cheaper.

The test would be easy for anyone with a supersoaker. Trial 1: Distance achieved with water alone. Trial 2: Distance with water and some corn starch. Trial 3: Distance with water and polyox (available at science hobby stores).
 — bungston, Jan 02 2004

 //What your idea wants is not alternating water-air, but water 'bullets' being accelerated by a high pressure blast of air, more like a paint-ball gun.//

 Yes, similar to that, but faster, to get the machine-gun-like effect. Picture the bits of water going down the tube, with high-pressure blasts of air in between. The air-water alternation simply speeds up the process you described so that you can get maybe 20 'bullets' per second. Remember, the objective in most squirt fights is not just to get the other one wet, but to really soak them.

 [DrCurry] I only implied that it would take longer, not be harder. What on earth gave you that impression?

[b'ton] Might just have to try it.
 — galukalock, Jan 02 2004

 Good link, [xrayTed]. I had forgotten about automatic markers. Actually, I could probably use the very same priniciples somehow to fit this application. In fact, why wouldn't a CO2 cartridge work for the air supply? I can think of no reason.

[humanbean] That's a very interesting mechanism, but I'm not sure how to adapt it to this. Ideas?
 — galukalock, Jan 02 2004

 CO2 may not work for two reasons: they are not 'field-rechargeable'; also, the rapid discharge of CO2 in full-auto mode might cause the valve assembly to freeze. I imagine there would be a certain residual amount of water in the chamber, which would freeze and jam things up.

I imagined something similar to a bicycle pump, with a 'standard' water-gun type pressure pump and valve. The plunger, or piston, would be spring loaded, with a ratcheting mechanism to hold the spring back. Pull back the ratchet (and plunger), then compress the air with the pump. Then release the ratchet. As air is released (by pulling the trigger), the spring expands, pushing the plunger in and maintaining some of the original pressure. Really the same principle as in the first link, only with a greater air volume and pressure.
 — xrayTed, Jan 03 2004

Musing along my corn starch annotation, it occurred to me that there might be a market for a watergun in the form of a hybridized pump action shotgun and marital aid which fired gluey corn starch / water bursts. This would be for those college-years water raids, not the grade school set.
 — bungston, Jan 03 2004

GREAT IDEA!!!
 — croissantz, Jul 18 2004

Baked. Woefully baked. I had one as a child, and I found mention of a rapid fire water gun on some aqua nerd's website.
 — notmarkflynn, Feb 16 2006

 I have an alternate explanation for why the alternating water/air travels further than the stream of water:

 When shooting the stream of water, the compressed air in the hydraulic reservoir is expanding a short distance, adding a relatively small amount of kinetic energy to the water leaving the toy.

When shooting alternating water and air, some of the compressed air is leaving the reservoir, and expanding in the barrel of the gun, in between bits of water. Since the compressed air expands a greater amount than it otherwise would, more of it's energy is transferred to the water.
 — goldbb, Aug 26 2011

 // I had one as a child //

As did I and half of my friends. I can't even remember the brand name, though it was different from the one in [/m.flynn]'s link, which just goes to show how very baked this is. Sorry.
 — Alterother, Aug 26 2011

Carbine-ated water?
 — 2 fries shy of a happy meal, Aug 27 2011

<SLAP>
 — 8th of 7, Aug 27 2011

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