first post, first water gun

Build a homemade water gun or water balloon launcher and tell us about it.
klrluvr
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first post, first water gun

Post by klrluvr » Sun Jun 29, 2008 7:59 am

Hello there fellas..(and ladies if there are any),
I am almost done with my first water cannon. It has been tested without the pump, using a hose quick connect with shut-off, and the kitchen faucet to pressurize the LTR. Blasts the water out pretty good. What is notable about it is the trigger valve. I used a little knowledge gained from building pneumatic spud guns to design it. Its housed in a 1 1/4" cross and uses a 1" o-ring sealed piston with a spring behind it, and a rubber sealing face that presses on the back of the barrel to operate.

I have a few bugs to work out of the design, but it seams like a very promising idea. The main bug is that the spring has to be very strong to fight the pressure created by two thick layers of LTR, and close the valve after you let the trigger go. I have some ideas to remedy this, but first I'm going to try a stiffer spring.

The other two ideas... 1) seal the pull shaft instead of the piston, allowing water pressure behind the piston as well as in front of it, reducing the back pressure on the piston dramatically.

2) keep the sealing face on the piston the same size, but reduce the size of the o-ringed portion down to possibly 3/8" or so, which would also reduce the back pressure, and also help with the friction created by the o-rings against the pipe wall.

This may be hard to understand, but I don't have time to draw a diagram right now. I will take some pics of the gun and draw a diagram in MSpaint to explain the internals of the "barrel sealing piston pull valve" as soon as I have time.

For all I know this is an OLD idea here at sscentral, but I haven't seen it here yet in my searches. If I get it working perfectly though I think it will be a hell of a thing for others to use.

I just couldn't allow myself to build a water gun that used a ball valve as the trigger. It just seams odd to have to open AND close the trigger, and at the same time your hand is in a weird place. This valve will make the gun seam more like a store bought water gun I think.

Any how, its late and I should be going to bed.

Cool web site by the way, I had a lot of fun reading through it and trying to take in all the info so far. My nieces and nephews are going to appreciate it too...hehe.

Oh, also, my screen name does not stand for killer lover, it means KLR lover, as in the Kawasaki KLR 650 dual sport. Because I'm having lotsa fun with it this summer :) . Just thought I would clear that up.

Happy squirting,
Chris

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SSCBen
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Re: first post, first water gun

Post by SSCBen » Sun Jun 29, 2008 11:52 am

Welcome to SSC!

Not too many people have tried homemade piston valves but they're a valid idea. Pre-2003 Super Soakers generally used piston valves. The full bore of a ball valve typically is all you need and you can make them trigger operated so that's fine for most people. The only real disadvantages to a piston valve are construction time and potentially bad flow paths that would create turbulence in the dihydrogen monoxide matter stream (sorry, my brother said that to me earlier and I couldn't resist repeating). But, the bad flow paths' effect is minimal so the only real disadvantage is construction.

I don't quite understand the ideas you mentioned so I'll wait for pictures and a drawing. Generally the biggest design flaw with piston valves is that the trigger can be hard or impossible to pull at high pressure, so anything to reduce trigger force is great.

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Silence
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Re: first post, first water gun

Post by Silence » Sun Jun 29, 2008 3:21 pm

Welcome to Super Soaker Central, Chris! We don't have any female members at the moment (at least, none that I know of), but you may remember joannaardway from a year or so back.

50 PSI (estimated)
5/8 * 5/8 * pi = 1.43 sq.in.
50 * 1.43 = 72 pounds of force

Eep...that's a lot of force! If you do use a spring with that strength, make sure it's mounted well. Unless my mental picture is wrong, which I think I do. Is the barrel 1"? Is the O-ring inside the barrel or inside the inlet pipe, opposite the barrel?

Pull valves have been considered before, but used mostly in Nerf. Most, like this Nerf one and this semi-auto one, have a plunger sliding inside the end of the barrel, with the inlet in the wall of the barrel. Scavenger has experimented with pull valves in his homemade. And Ben has considered pull valves that use a sealing face instead - easier to build, but opening and closing the valve reveals and hides a sealing face, which suddenly changes the net force acting on the plunger because of the pressure acting on the new face.

On the whole, water gun builders don't really build valves themselves. There's little incentive, as opening speed is irrelevant for us, and ball valves provide plenty of flow. But if you want a real trigger, a pull valve can't be beat. Thanks for making this thread, and good luck with the build! :)

aEx155
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Re: first post, first water gun

Post by aEx155 » Sun Jun 29, 2008 3:26 pm

The dangers of dihydrogen monoxide...

Is he talking about the piston valves used in pneumatic spudguns? I've never heard of them before, and any search I do brings up the launcher variety...

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Silence
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Re: first post, first water gun

Post by Silence » Sun Jun 29, 2008 3:29 pm

Yep, he's talking about those. They allow for both high flow and fast opening times, both of which are critical in launchers (but deadly in water balloon launchers, as the balloons will just explode). Basically, you open a pilot valve that removes the air on one side of the piston. That creates a pressure differential that, applied across a valve with large area, exerts a lot of force to quickly open the valve. See these diagrams.

aEx155
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Re: first post, first water gun

Post by aEx155 » Sun Jun 29, 2008 3:37 pm

SilentGuy wrote:Yep, he's talking about those. They allow for both high flow and fast opening times, both of which are critical in launchers (but deadly in water balloon launchers, as the balloons will just explode). Basically, you open a pilot valve that removes the air on one side of the piston. That creates a pressure differential that, applied across a valve with large area, exerts a lot of force to quickly open the valve. See these diagrams.
Well, I know what those are, it's just that, the way he's describing them confuses me; I know the piston valves don't have pull shafts, so I'm not sure whether or not he's talking about those, or something different related to water guns...

klrluvr
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Re: first post, first water gun

Post by klrluvr » Sun Jun 29, 2008 3:59 pm

Looks like I have peaked a little interest HOOHAHAHAHAAA< (evil mad scientist laugh).
Quote: BEN SAID I don't quite understand the ideas you mentioned so I'll wait for pictures and a drawing. Generally the biggest design flaw with piston valves is that the trigger can be hard or impossible to pull at high pressure, so anything to reduce trigger force is great.

I will get the pics and stuff up, but I have to leave today for a family reunion. And yes, trigger pull is a problem, but as silentguy mentioned as soon as the valve is opened a little bit the force of the water pressure is on your side.

Quote: SILENTGUY SAID Eep...that's a lot of force! If you do use a spring with that strength, make sure it's mounted well. Unless my mental picture is wrong, which I think I do. Is the barrel 1"? Is the O-ring inside the barrel or inside the inlet pipe, opposite the barrel?

It is a strong spring, but the gun is built like a tank. The o-ring is mounted in a piston I cast out of epoxy. The piston rides in the 1" pipe opposite the barrel, and has a rubber sealing face on the front of it, that gets pressed against the polished back end of the barrel. The inlet is actually on the bottom, and the pipe to and from the pressure chamber comes out the top.

I will get the pics and diagrams up as soon as I can, I promise. I will add them to this thread.

BTW, my sn at spudfiles is Lockmanslammin for those of you that go there.

Thanx for all the quick replies.

Chris

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SSCBen
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Re: first post, first water gun

Post by SSCBen » Tue Jul 01, 2008 2:15 am

Sounds great. We all know (too well, in fact) what personal things can get in the way. Between procrastination and interruptions I think it's a miracle I do anything. :p
It is a strong spring, but the gun is built like a tank. The o-ring is mounted in a piston I cast out of epoxy. The piston rides in the 1" pipe opposite the barrel, and has a rubber sealing face on the front of it, that gets pressed against the polished back end of the barrel. The inlet is actually on the bottom, and the pipe to and from the pressure chamber comes out the top.
Sounds nice. I've never considered casting epoxy before so I'd be interested in seeing how that works/looks. Overall it sounds rather simple, just like a normal pull valve.

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Drenchenator
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Re: first post, first water gun

Post by Drenchenator » Tue Jul 01, 2008 1:01 pm

Welcome to SSC!

I'm interested in these ideas as well. Not too many people build valves here because for the most part ball valves are good enough. Still, I'd love to see some pictures or diagrams of the piston valve you're talking about. I was the guy who built the semi-auto valve assembly discussed before, so I know a little bit about making valves.
The Drenchenator, also known as Lt. Col. Drench.

klrluvr
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Re: first post, first water gun

Post by klrluvr » Tue Jul 01, 2008 4:49 pm

Image

first try on posting a pic, let me know if you have any questions, that is if the pic posts correctly anyhow.

Chris

aEx155
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Re: first post, first water gun

Post by aEx155 » Tue Jul 01, 2008 4:59 pm

It looks like you posted it correctly. I can see the picture just fine; you might want to try posting a thumbnail and linking to the full image, rather than putting such a large picture, just so it doesn't take up so much space. You could also try attaching it to your post.

Nice way to make a piston based pull valve. Although the flow isn't as linear as it could be, it seems like it's working for your purposes.

Now that we have it picture, it's much easier to understand what your talking about. I don't quite get the second suggestion you made in your first post, but the first one sounds like a good idea.

Is everything reduced to 3/4" fro the 1 1/4" tee? You didn't provide any measurements in the picture, so I'm assuming it's 1" from your first post. I'm guessing that would put ~20 pounds of force (at 45 PSI) on the piston, so that is one beefy spring.
Last edited by aEx155 on Tue Jul 01, 2008 5:10 pm, edited 1 time in total.

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Silence
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Re: first post, first water gun

Post by Silence » Tue Jul 01, 2008 5:56 pm

Looks good, and thanks for the clean diagram. Mine are similar on graph paper, but naturally messier and with pencil smears. :rolleyes:

You're going to have some serious changes in net force on the piston thanks to the disappearing and reappearing sealing face. It'll take 20 pound of force to pull back the trigger, then only a light touch to keep it open. You may want to rearrange the components to get a chamber-sealing valve.

Even then, make sure you get the spring lengths and force constants right. It's better to have a 22 inch spring with a force constant of 1 pounds/inch compressed into 2 inches of space - yielding 20 pounds of force and 1 extra pound (from your finger) to pull the trigger back another inch. A shorter spring with a higher rate would require much more force to pull the trigger back the same distance.

aEx155
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Re: first post, first water gun

Post by aEx155 » Tue Jul 01, 2008 6:16 pm

SilentGuy wrote:You're going to have some serious changes in net force on the piston thanks to the disappearing and reappearing sealing face. It'll take 20 pound of force to pull back the trigger, then only a light touch to keep it open. You may want to rearrange the components to get a chamber-sealing valve.
What's confusing to me is how pressure is affecting the piston. Under pressure, I'm assuming the water is trying to force the piston open; which means that the "high pressure" water region is trying to get to the "low pressure" outer region by pushing the piston back (away from the nozzle).

[skip this if you know how piston valves work]
In regular piston valves in pneumatic launchers, the pressure is equal on both sides of the piston bun not on the nozzle side, holding it closed ("pressurizing position"); when the pilot valve is opened, air rushes out lowering the pressure behind the piston ("fire position") and the high pressure forces it back opening the valve, and releasing the air.
[end]

Looking at this from a launcher perspective, this valve is always in the "fire position" and is never in the "pressurizing position", right? If the spring is acting as the air behind the piston, and your hand acts to counteract the spring, how would it become easier to hold open during firing?

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Silence
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Re: first post, first water gun

Post by Silence » Wed Jul 02, 2008 2:35 am

Note the pipe to the right of the cross. When the valve is closed, there's no pressure there. The water inside that section either seeps out of the nozzle or just sits there.

When you pull the piston back, suddenly there's pressure on that section. Because the pressure comes into contact with the sealing face of the piston, there's a new force acting on it there. So as soon as you pull the trigger, pressurized water suddenly pushes on the valve.

It's just like with a suction cup. When you press the cup onto a surface, you depress the rubber and squeeze out the air inside. Because there's more pressure acting on the cup from one side (the outside) than from the other (the inside), there's a net force pushing the cup onto the surface. As soon as you pull it off, the "pressurized" air rushes in and pushes back, equalizing the force.

klrluvr
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Re: first post, first water gun

Post by klrluvr » Wed Jul 02, 2008 4:47 am

Silent guy has it figured out pretty well aEx155. You do have to pull harder to break the seal, then once its open, it is easier to hold. Then it feels real weird when the water runs out, and the trigger yanks itself closed with surprising force.

SilentGuy, instead of scraping the whole valve I am going to be making an insert that will thread into the 1" threads and contain a small tube, maybe a little larger than 1/4" and there will be an o-ring sealed shaft going through that up to a new sealing face the same diameter as the original one.

But what you said in your last post has me wondering, will it still be just as difficult to initially open the valve? I may have to build a lever type trigger to add leverage and make it easier to pull, since the original intention here was to make it for kids to play with.

All experimental...trial and error. This is turning into quite the project. Oh well I like a good challenge.
Oh and by the way, the tube that the piston rides in is 1" the bottom is 1/2" and the other two are 3/4".

Chris

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