Questions...

Threads about how water guns work and other miscellaneous water gun technology threads.
myndzi
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Questions...

Post by myndzi » Sun Apr 30, 2006 10:17 pm

My dad works in pool/spa repair, so as a result there is plenty of spare pipe laying around, he has any tool I could possibly want, and I have experience laying and gluing pipe and such. This site has gotten me interested in trying to put together a water gun or two this summer for kicks. I've been reading all sorts of good information on the site and the forums today. A lot of it is still sinking in, but I had a couple questions I can safely say I have at least searched about for.

1) In designing a water gun, is the barrel necessary for any particular reason? Does it need to be a specific length? What exactly is it doing between the pressure chamber and the nozzle, other than getting water from here to there? Does the length of it have a significant effect on linear flow? Why is it different to have a larger pipe coming from the pressure chamber and narrow at the nozzel than to have a nozzle-sized pipe coming directly from the pressure chamber?

2) I remember playing with some 'surgical tubing' (LRT) years back with my dad, and it was good stuff. I am therefore more interested in a 'CPS' type gun than the others. What is the effect of air in the CPS chamber (outside of the tubing)? Is the CPS chamber sealed, thus adding the pressure of the air inside to the force of the tubing contracting, or is it vented so that the tubing is doing all the work? What would happen if the air outside the rubber tubing was pressurized?

Also, I have been reading a number of the articles and things which deal with specific aspects of building and design, but is there a thread or article I missed that goes over generally creating something from the ground up, and the choices involved?

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m15399
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Post by m15399 » Sun Apr 30, 2006 10:24 pm

1. The barrel is just a here to there type of thing. It probably does laminate the stream a bit, but it isn't too noticable.

2. The air is vented. If you pressurize it, there would be a lot of stress on the tubing and it will tear sooner than it would have if you didn't pressurize it.

There are several articles around here. I don't think there's one that comprehensive (I might write one, now that you gave me the idea ;) ), but if you look around I'm sure you'll find enough info.

http://www.geocities.com/m15399/homemades.html
That's my website. If you read those articles, that's pretty much a homemade from the ground up with a few choices.

Welcome to SSC! Nice first post. ;)

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Silence
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Post by Silence » Sun Apr 30, 2006 10:25 pm

Welcome to SSC, myndzi :) . And now to your questions...

1) The barrel is practically useless. It really doesn't serve a purpose in soakers besides for looks, and it won't increase stream lamination significantly (if at all). However, the point of having a large pipe from the PC to the nozzle is to allow for greater nozzle selection flexibility. While a narrow barrel might be fine for small nozzles, it will not work for large nozzles--it will restrict water flow and possibly add to the turbulence when the water arrives at the wider nozzle. Large barrels can work for small or large nozzles.

In addition, you will have to reduce the PVC size somewhere between the PC and the nozzle, so you don't lose anything by keeping a large diameter. Preferably, you will use a conical nozzle, which will help maintain lamination--more so, at least, than a PC to barrel reducer.

EDIT: I wrote before I saw m15399's post, but his answer to #2 is good. You don't want to pressurize outside the LRT (this has been proposed) because it could contort the LRT, etc. In addition, reliance on external air pressure could cause the soaker to become more like an APH--as the PC fills, the pressure goes up. That is the opposite of the CPS idea.

In addition, CPHs don't need PVC around them. If they have external PVC, it's only to protect the LRT, not to hold pressure.

myndzi
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Post by myndzi » Sun Apr 30, 2006 10:35 pm

Thanks for the rapid response. I thought of another one that I may be able to phrase briefly:

Has anyone devised a CPS system that allows you to fill the LRT from one end and fire it from the other? Is it worth bothering with? I think that it can be done in a number of ways. It seemed like being able to fire from the front with no barrel to speak of and fill from the back could be useful both by creating a smooth firing path (no pipe/valve for water intake in the firing path) and by allowing the most travel/leverage on the pump itself, which would be moving water at the back of the gun. Am I making any sense?

Edit: Just wanted to mention I am also browsing your site, so I apologize if I am talking before having read everything...

Also, the nozzle flexibility thing makes a good deal of sense, I'll be keeping that in mind.

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Silence
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Post by Silence » Sun Apr 30, 2006 10:40 pm

@ m15399: You have a nice site--I can't believe I haven't been there before! It's quite clean and accurate.

If there is any problem with it, you say that APHs give the most bang for your buck. However, Ben has been suggesting that everybody switch to CPHs, because (1) they provide superior performance and (2) they are cheaper. Yes, that's right--due to the lack of reducers and such, CPHs are simpler and require fewer different components, even though one of those parts (the LRT) may be slightly harder to obtain. Overall, CPHs are the cheapest soakers to build and they provide the best results.

Of course, I'm going to build my PCgH soon, and although it will be more expensive, I hope it will have similar battle practicality to CPHs.

EDIT: Didn't see the latest post--again! Here's my answer:

Okay, it's funny: I recently proposed the same idea, but Ben explained the problems. I'll try to find that thread, and I'll put the link in this thread.

EDIT again: I found the thread: "New latex rubber tubing came in." Post #s 4 and 9 are the relevant ones.
Last edited by Silence on Sun Apr 30, 2006 10:45 pm, edited 1 time in total.

myndzi
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Post by myndzi » Sun Apr 30, 2006 10:55 pm

I actually read through that thread, but I guess I didn't make the connection -- still don't. I see what you are talking about now, and it's not exactly what I had in mind. I know that the tubing has to be able to expand lengthwise, so what I was pondering was something like this:

You have the tube attached directly to the firing path on one end, which leads to the trigger and the nozzle (if you wanted one, I guess). On the other end, you'd have a bit of a contraption. There'd be a fitting that the LRT stretched slightly around and was affixed to, that was hollow in the center with a seal; this would fit over a smaller pipe that had an outer diameter approximately equal to or lesser than the inner diameter of the LRT. It might even work if it was a bit larger; I think the rubber expands where it is stretched first, so the part surrounding the pipe would expand and thus not drag along it? Anyway, that part I'm not sure about.

Edit: I should mention that the fitting slides along the pipe all the way to the back as the LRT expands -- I was going to mention that specifically but forgot. You'd pick the lengths based on the length of the unexpanded tubing and the length of the expanded tubing.

What is guaranteed is that the input provides for less volume than the output, and I'm not sure how well you could make the seal move and slide (I assume similar to the piston tech discussed in other places). Those are the parts I was curious about. :)

Edit2: Now with crappy paintbrush picture.

Image
Last edited by myndzi on Sun Apr 30, 2006 11:14 pm, edited 1 time in total.

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m15399
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Post by m15399 » Sun Apr 30, 2006 11:34 pm

That might work in theory, but in practice, there's no way to hold the pressure and let it slide at the same time. You might be able to do it by hooking some flexible plastic tubing to one end...

Silent Guy, In my opinion, you need large reducers and pipe to make a proper CPH, so the APH would be cheaper.

myndzi
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Post by myndzi » Sun Apr 30, 2006 11:40 pm

Hmm, well that's what I was asking, so I will discount the idea for now... I didn't want to delve into the pump stuff which I wasn't even sure would apply here. I'll put some consideration into a design and put it up here for feedback sometime later if I can. Thanks again for your help (all of you).

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Silence
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Post by Silence » Sun Apr 30, 2006 11:43 pm

Image
So this is what you wanted? My diagram only shows the essentials; obviously, you would need a pump, another check valve, possibly a reservoir, etc. to complete it. You would also need a pump piston to barrel connector for a grip and to support the barrel and nozzle. You could also use PVC to encase the PC for support and protection, but then you couldn't use the ball valve like a trigger.

EDIT: Argh! I didn't see the last two posts! Actually, it doesn't matter too much...

This design should work--the pressure and rubber contraction would cause the piston-thing to slide, and there is no reason for the seal to fail. Of course, there may be some turbulence within the PC, but I'm not sure.

About the APH-CPH price difference, I think Ben is the expert here. I don't know much about it.
Last edited by Silence on Sun Apr 30, 2006 11:51 pm, edited 1 time in total.

myndzi
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Post by myndzi » Sun Apr 30, 2006 11:50 pm

Ha, no problem. I've been checking back and forth between other stuff to keep an eye on this and replying, since it was moving so fast. I think you have the idea, the question is if the sliding seal bit is feasible or not, which m15399 said probably wouldn't work. I'm open to ideas, but I'll probably be thinking in more standard directions unless someone more experienced can tell me it's worth persuing...

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Silence
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Post by Silence » Sun Apr 30, 2006 11:52 pm

I didn't see the last post. As I said above anyway, however, the sliding seal should work.

myndzi
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Post by myndzi » Mon May 01, 2006 12:02 am

Edit reply edit edit reply edit edit! That's the only reason I'm posting more than editing, really.

I don't know what kind of pressure is going on inside the tubing. Turbulence doesn't seem like it would be any different than otherwise, maybe less since the tube is held 'straight' instead of being weighed down by gravity. Do you think the sealing methods described in the articles on creating the pumps would be adequate to hold here, then? By all accounts I'd have to do some testing anyway, but I'm trying to find a good place to start.

That aside, is it even worth the effort? I liked it because of how it would let me lay the rest of the parts out, but that's a rather fluid seeming decision at the moment.

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m15399
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Post by m15399 » Mon May 01, 2006 12:15 am

What are you planning to use for the seal? I can't think of anything that would slide as well as hold the pressure while restraining the LRT from flying off.

myndzi
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Post by myndzi » Mon May 01, 2006 12:20 am

I'm not planning yet... ;)

The LRT is going to overlap the pipe that fills it by enough space that there is no risk of it flying off... when it expands, it will encompass more of the fill pipe. I don't know yet what kind of considerations I will have to meet to have a sliding seal that won't leak water. I'm open to suggestions. It looks like some sort of lubricant would be useful too, there were a couple suggested in the pump articles... the smoother it slides, the better of course.

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Silence
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Post by Silence » Mon May 01, 2006 12:57 am

I agree, this is a very active thread, and new posts are the only way to keep up. Nobody is holding it against you.

Once again, I don't think you need to worry about the seal leaking. After all, if the seal will hold when you pump water into an 80 PSI chamber, then it should hold if it is part of an 80 PSI chamber.

Yes, smooth sliding was my initial worry, too. A lubricant should easily do the trick.
myndzi wrote:I liked it because of how it would let me lay the rest of the parts out, but that's a rather fluid seeming decision at the moment.
A "fluid seeming decision"--that makes a good pun :p .

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