Water cutter

Threads about how water guns work and other miscellaneous water gun technology threads.
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kevinthenerd
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Water cutter

Post by kevinthenerd » Wed Apr 05, 2006 4:38 pm

A water cutter shoots a small stream (about the thickness of a human hair) at speeds of Mach 3 at pressures of about 60000-80000 psi. Do you have ANY idea how that is accomplished with standard steels? Is there anything that can be borrowed from that technology to make a water gun capable of a 100+ ft. range?

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SSCBen
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Post by SSCBen » Wed Apr 05, 2006 9:13 pm

From what I have seen and read, water jet cutters use extremely thick chambers to contain the extreme pressures. When introduced to the thought myself, I wondered how they contained that much pressure. Of course, I am no expert in water jet cutting, but there are a few people here who would be (i.e. Chris Bloch).

The speed comes simply from the nozzle orifice diameter. When the diameter is about the size of a hair and the pressure is that high, the velocity is going to be enormous. Mach 3 isn't too unbelievable actually.

If you are looking for more information, HowStuffWorks is a good place to start if you haven't seen their page already: http://science.howstuffworks.com/question553.htm

As for how water jets can help us, they have in many ways. I read loads of patents, and one such patent was of a nozzle by an inventor named Chris Bloch. The nozzle was designed to be a more efficient water jet cutting nozzle, designed to achieve far greater cohesion than a normal nozzle. Of course, the same principles can be applied to a water gun nozzle. In fact, Buzz Bee Toys is looking at the same patent to use in their 2007 water gun line. Look at the water nozzle patents thread for more information on this (it should be in the "Water gun physics" category).

Looking at the HowStuffWorks page, I have noticed something new: "SuperWater." This sounds like a super-additive, and given the picture displayed on the homepage, it sure is! It still would probably be cheaper and safer to use glycerin however.

Also on the links section of the HowStuffWorks page, there also is a link to "The Cutting Fire Extinguisher" which looks really neat. That gun packs quite some power if it can cut through metal as it was intended to!

As for getting 100+ foot distances, that is easily possible. You can buy existing systems that already get that much distance such as golf field sprinklers. You also can use a bunch of additives on a more powerful water gun and likely get that much distance. The problem is getting over about 65 feet of distance without making a design that is not mobile or useful. I'm finishing up my water gun that should be able to get 75 feet of distance without additives and extreme pressures. You should know how that works out by the summer.

Big Bee did detail a water gun that can shoot easily over 100 feet to me via email once. Essentially, you'll need a nozzle orifice diameter of 1/2 inches or larger, an internal diameter of over 2 inches, and a larger pressure chamber 3 inches or greater in diameter, capable of containing over 200 PSI safely. You'll also need to design the water gun and nozzle in a specific manner, which I have done on a smaller scale in my distance water gun. Pressures greater than 175 PSI likely will be required to achieve the distance also.
Last edited by SSCBen on Wed Apr 05, 2006 10:09 pm, edited 1 time in total.

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Silence
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Post by Silence » Mon Apr 10, 2006 3:17 am

I've got a theory: By using a smaller (conical) nozzle size, one should be able to get relatively more output per opening area. I state this because there should be more pressure inside the barrel and PC(s), so besides greater resistance and turbulence, water should be coming out of the nozzle faster. With this greater pressure and velocity, why are small nozzles not recommended for long-distance shooting? Keep in mind that the stream may be more laminated as well.

I am completely against the use of chemical enhancements, quoted in Ben's streams article and in this thread, because I simply don't trust them. They could (1) damage one's blaster, (2) damage the environment, (3) be commercially unobtainable or similarly rare, (4) completely change the idea of water warfare...I could go on for quite a while without having my list of ideas drying up (ha ha, "drying up," :rolleyes: ). If one tried widely marketing such chemicals, many soaker fans (myself included) could easily retaliate by spending ex-chemical-money on the parts for a pretty impressive soaker...

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SSCBen
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Post by SSCBen » Mon Apr 10, 2006 10:19 am

You're right, an increase is output also likely exists if a conical nozzle is used. I don't believe that the increase in output would be very substantial though, but I say this mainly because some people have a tendency to read anything and everything said about increasing distance and output and ask me how much it would increase distance/output, etc. when it really is insubstantial.

As for additives, most people won't use them to begin with. Glycerin is a naturally occuring compound that's in the foods we eat and is cheap, so it's the only additive so far in my mind. It still is far too expensive for regular use however.

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joannaardway
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Post by joannaardway » Mon Apr 10, 2006 9:19 pm

Small streams break up more, so thus, they aren't recommended for long range shooting.

The dilemma:

Small streams have a greater velocity, but break up more
Big streams have a lower velocity, and break up less

The trick is to hit the mid point between the two for range, so incredibly small isn't excellent, neither is incredibly big. There is something in the "Streams" article about finding this ideal mid point.

As a side note, that "superwater" looks really good.

Think about it logically - at concentrations of only 0.3%, one litre of the stuff will do over 330 litres of water (around 37 full fills of a CPS 3200), compared to a litre of glycerine doing about 20 litres (a bit more than 2 fills of a CPS 3200).

This quantity, being over 16 times more, must make it cost effective compared to glycerine (and, visually at least - going by the images, it appears more effective)- so if it were available in small amounts (and it's safe), it would be excellent for range boosting, assuming no unforeseen factors.
"Over the hills and far away, she prays he will return one day. As sure as the rivers reach the seas, back in his arms again she'll be." - Over the Hills and far away, Gary Moore

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Silence
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Post by Silence » Thu Apr 13, 2006 2:37 am

Joannaardway, I understand your point that smaller streams may break up more over larger distances, but this assumes that there is at least somewhat poor lamination. Ben's mathematics in his Streams article can't exactly predict the effects of different levels of lamination--but if I'm wrong, I'd like to know the correction, please :D .

With reduced lamination, I stand by my statement that smaller streams are better for range--and I'm expanding that to cover all practical use, because as I stated earlier but with less emphasis, the output should be close to that of larger nozzles.

Why do soakers using larger nozzles provide greater output than those using smaller nozzles? The answer involves the fact that the design of guns, especially those with nozzle selectors, simply restricts output from smaller nozzles instead of channeling it. If we DIYers can design and build soakers with laminated streams (linear design, high pressure/good nozzle, etc.) and a non-restricting design, then we will have revolutionized the industry :cool: .

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Silence
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Post by Silence » Fri Apr 14, 2006 10:58 pm

I doubt anybody can build a personal water cutter :rolleyes: , but we can come close enough to obtain a greater velocity. I have plans to build the PCgH that I have been detailing in the Homemade Water Cannon forum, and it will hopefully have enough power and stream lamination to use a smaller nozzle effectively. Once I finally perform these tests, I will post the results here.

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joannaardway
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Post by joannaardway » Mon Apr 17, 2006 12:59 pm

A perfectly laminar narrow stream will still break up in air.

The air itself will cause drag against the stream, and the head of the stream will still be pushing against air and decelerate as well. This slowing down contributes to the stream breaking apart.

And as another point - a narrower stream is harder to laminate because:

a) if you reduce the internal diameter to improve it - the ratios of the pipe area to pipe circumference increase friction

b) if you reduce from a large internal diameter, that naturally disrupts the lamination of the flow (if you don't believe me - go and do A-level physics)
Last edited by joannaardway on Tue Apr 18, 2006 3:30 pm, edited 1 time in total.
"Over the hills and far away, she prays he will return one day. As sure as the rivers reach the seas, back in his arms again she'll be." - Over the Hills and far away, Gary Moore

"So many people have come and gone, their faces fade as the years go by. Yet I still recall as I wander on, as clear as the sun in the summer sky" - More than a feeling, Boston

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SSCBen
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Post by SSCBen » Mon Apr 17, 2006 3:56 pm

As joanna said, increasing lamination does not completely eliminate the effect of drag. Increased lamination will keep the stream together for a longer period, but there is no way to reduce the effect of drag on the stream.

Smaller streams are much more affected by drag for several reasons. The first reason is the fact that the small streams have a greater velocity at the same power and velocity greatly affects the drag on the stream. The smaller streams also have less water to move by drag and less momentum.

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Silence
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Post by Silence » Tue Apr 18, 2006 1:46 am

On the defensive side, I don't think I stated that lamination reduces drag to improve range--but it does keep the stream together more, as everybody has said, making it much more effective at long range.

@ joannaardway: for point "a," the ratio of the pipe diameter to pipe circumference will always be the same (1/[pi], to be exact) :p --and I don't what any of this has to do with friction. Could you please clarify this?

Also @ joannaardway: for point "b," I have already suggested a professional, conical nozzle to help reduce stream turbulence as the pipe width decreases. It's the best we can do. And anyway, there will be quite a bit of turbulence from this whether the orifice is large or small.

Now @ Ben: we all know that momentum depends on mass, and for a substance of a specific density, it depends on volume. We can model a stream using a cylinder with volume (pi)(r^2)h, where r is the radius and h is the height of the cylinder/length of the stream. For our purposes, this height is a constant (though another benefit of a smaller stream is that the duration can be n^2 longer, where n is the large orifice radius divided by the small orifice radius ;) , unless the pressure/velocity of the stream increases--and that isn't bad at all). Clearly, the volume/mass/momentum is directly varied with the base area, r^2, of the stream--but so is the front-end fluid air resistance :eek: ! This nullifies your point, because the ratio of the front-end friction to the volume/mass/momentum is a constant, and the radius/diameter of the stream will not matter :p . Needless to say, you'll get farther range with a smaller stream radius because its velocity will increase at least a little bit :cool: .

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SSCBen
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Post by SSCBen » Tue Apr 18, 2006 10:17 am

No, you won't get maximum distance from a smaller nozzle. That's not true at all. I won't say that distance decreases equally as the nozzle gets larger and the nozzle gets smaller (that is, decreases evenly on both sides), but I will say that the best nozzle size always is a moderate one.

I don't think that you're getting my point anyway. My point was the something of less mass has a tendency to be affected by air resistance more because they typically have less momentum. Of course, I wasn't completely sure about this after I thought about it - would different size nozzle orifices have the same initial momentum? If the stream is smaller, velocity will increase, and if the stream is larger, velocity will decrease. Sounds interesting.

Besides, I've done extensive testing with lots of nozzle orifice sizes and I know that small nozzles do not get maximum distance or even close. Regardless of the theory behind it, they simply don't get maximum distance. Moderate sized nozzles get the advantages of both.
@ joannaardway: for point "a," the ratio of the pipe diameter to pipe circumference will always be the same (1/[pi], to be exact) --and I don't what any of this has to do with friction. Could you please clarify this?
Smaller pipes have more friction because a larger amount of the flow is touching against the pipe. I believe that's what he was referring to. Friction however is mostly negligible unless you have a long length of pipe.

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joannaardway
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Post by joannaardway » Tue Apr 18, 2006 3:51 pm

Sorry, there was a mistake with point a)

"diameter" should have read "area"

The ratio of circumference to area is as so:

2[pi]r/[pi]r^2 = 2/r

You want the smallest circumference for the area, so a larger ID is good.

An ID of 2 cm results in a coefficent of 1

An ID of 5 cm results in a coefficent of .4 - this lower number being better in terms of friction.

Reducing the ID with a conical nozzle is not ideal - the coefficent changes, producing eddies and turbulence.

The slower the co-efficent change the better, as less turbulence is created as water from the rear of the stream has a velocity less great than that in front of it for a given "lower area change relative to circumference change gradient density unit length" (quite a keyboardful).

In other words - a long conical nozzle is better than a short one, or a screw-on endcap. Any rapid change in ID is very bad for lamination (and any change is not benifical)

Ideally, a water gun would be entirely linear, with the same ID every where, but this isn't in anyway possible - save for one case.

- A piston type, with no valves, just one long tube, with a pump in it (facing backwards to normal). The pump forces the water straight out of the end of the pipe. Think - the ultimate in laminaton.

@Ben: Not the right place I'm sure, but I believe that your use of the "friction in plastic ducts" table was misunderstood. I'm sure it means "equivalent feet of pressure lost per 100ft of pipe" rather than "feet of range lost per 100ft of range" - those tables weren't designed for water guns specifically.

I also hope you didn't mean "he" in:
I believe that's what he was referring to.
"Over the hills and far away, she prays he will return one day. As sure as the rivers reach the seas, back in his arms again she'll be." - Over the Hills and far away, Gary Moore

"So many people have come and gone, their faces fade as the years go by. Yet I still recall as I wander on, as clear as the sun in the summer sky" - More than a feeling, Boston

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SSCBen
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Post by SSCBen » Tue Apr 18, 2006 10:11 pm

Over the years, we haven't had too many female members, so please correct me when I address you incorrectly. It's not that I forget, rather, I am used to typing that way. ;)

As for the friction table, I really had no idea what the friction table actually meant at the time. One of my humbling moments. I did get the important part at the time - the friction of larger ID pipes affect fluids less.

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Silence
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Post by Silence » Wed Apr 19, 2006 12:09 am

@ joannaardway: I guess I didn't see that you had said area, and not diameter/ratio (unless you edited it just now...grrr). But I can see your point now, whether the friction is important or not. In addition, your concept of a water gun with perfect linear design would require the feed to the pump to come right through the pump handle--just for pointless information, of course :D .

@ Ben: if I ever said that smaller nozzles get more distance, then I take that back. I trust your experience, because I have really only been theorizing--but maybe conical nozzles might help alter the range disadvantage that smaller nozzles have toward average nozzles.
Last edited by Silence on Thu Apr 20, 2006 1:21 am, edited 1 time in total.

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kevinthenerd
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Post by kevinthenerd » Wed Apr 19, 2006 2:30 pm

joannaardway wrote:A perfectly laminar narrow stream will still break up in air.
That's true, Joanna. At the nozzle speeds required for the desired range, there would be a lot of viscous effects present between the air and water. Surface tension is only so strong. A larger nozzle would have a water stream capable of absorbing this energy internally without resorting to breaking the all-important surface tension keeping the whole thing together, but the major disadvantage I can see already to a large nozzle is that it would quickly empty the chamber at high muzzle velocities.

Nozzle design, it seems, is going to be the most critical aspect of my design. One idea I recently had was to deisign a system that "wraps" the water with a blanket of air shortly after leaving the gun to absorb turbulent energy, using high air pressure instead of putting the surface tension in jeopardy. I think this would yield better agglomeration without introducing the viscosity of a solid chamber. (The air flow is going to be partially parallel with the water flow, cancelling out any relative velocity effects.)

Final exams are next week, so I won't be able to sit down and design this for some time. Until then...

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