Homemade design advice.

Build a homemade water gun or water balloon launcher and tell us about it.
frankenbike
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Post by frankenbike » Tue Jun 21, 2005 4:26 am

I've been carrying on a conversation at isoaker.com, and thought I'd discuss some elements of a gun I'm proposing for a water war among adults.

The water war will take place in a public area with no water outlets or power available. There will be at least 40 people involved.

To recap:

During the course of the conversation, I decided I wanted to make a backpack water gun with at least a 2 gallon capacity. I've settled on two things:

1. It will be a pressurized tank delivery system using schedule 40 or 80 PVC. Right now, I'm thinking two foot-long 6" pipes.

2. It will be pressurized using a CO2 tank like the paintball guys use. These hold about 1 lb of CO2 in a tank the size of a big beer can. That's the equivalent of about 40 of those small CO2 cartridges, and can pressurize 33 liters of air to 100psi. The CO2 tank is pressurized at 800-1000psi. I'll be using a regulator designed for that pressure with an output pressure gauge. It costs $3-5 to refill the tank.

I expect to be running the system at a constant pressure between 60 and 125psi.

I thought I had settled on using a modified garden hose, gun style trigger/valve with a 6" solid brass straight stream nozzle.

But I've been looking at pressure washer guns and nozzles, running a 12" 1/4" inner diameter "lance". It seems people are getting pretty good distances at this size nozzle. But it's an upper limit for those guns. There's only one I've found that has a 3/8" outlet lance size.

The reason I'm considering a pressure washer gun and lance system is pure cosmetics. With their insulator coverings, the lance systems look like assault water guns.

Does anyone have any experience using pressure washer guns?

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Scavenger
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Post by Scavenger » Tue Jun 21, 2005 1:37 pm

It sounds like a good idea, but that will be extremely heavy. 6" pipe 2 feet long is slightly overkill. But it you can get it to work, you'd be feared. Good luck. :D

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SSCBen
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Post by SSCBen » Tue Jun 21, 2005 2:19 pm

Welcome to Super Soaker Central frankenbike and Coco Man! Both of your accounts have been upgraded.

I actually recommended the two feet of 6 inch pipe, which isn't a bad idea in my opinion. Doing the math, that is about 11 liters of water, which is less than 25 pounds of water. Now, while that sounds heavy, frankenbike is planning on finding a cheap frame backpack to mount it all on, which would make him able to carry significantly more weight more comfortably than before.

Even if it was too heavy, he could fill the backpack less to keep it lighter. ;)

Other than that, please read my other earlier reply at iSoaker.com, frankenbike.

frankenbike
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Post by frankenbike » Tue Jun 21, 2005 5:36 pm

Originally posted by Doom@Jun 21 2005, 07:19 AM
Welcome to Super Soaker Central frankenbike and Coco Man! Both of your accounts have been upgraded.

frankenbike is planning on finding a cheap frame backpack to mount it all on, which would make him able to carry significantly more weight more comfortably than before.

Even if it was too heavy, he could fill the backpack less to keep it lighter. ;)

Other than that, please read my other earlier reply at iSoaker.com, frankenbike.
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Not just a backpack, which in the general parlance of these groups means shoulder mounted backpack, but I'm looking at getting one with a waist belt. That takes the load off the shoulders as well. I hiked nearly 50 miles in the mountains at one time with a 60 pound pack that way.

When I'm not using it for a soaker, I can fill the backpack with water and pretend I'm on a heavy gravity planet while I exercise and try to build my legs to the size of tree trunks.

I'm definitely "weighing" the other issues. I guess I'm going to be a trail blazer on the power washer gun.

It's interesting. A lot of the issues in homemade water gun design center around pressure preservation. But what happens when you essentially can vary the pressure at will to whatever level you want? Lose some pressure because of tube wall friction, add a little more at the head end by turning up the regulator.

If I managed to find Schedule 120 pipe, I could probably safely pressurize the tanks to 300psi. I don't think even a CPS2000 ran pressures as high as 100psi. And with those huge nozzles of theirs, the water doesn't last very long.

Still, if anyone does find someone who has experience with a pressure gun soaker, even one that uses a high pressure washer system to drive it, I'd like to hear about it.

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SSCBen
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Post by SSCBen » Tue Jun 21, 2005 8:22 pm

I know you're talking about a frame backpack with a belt. I biked most of the C&O canal while wearing one. Carrying 25 pounds of water on a frame backpack without a belt would be damaging to your back. I suppose I don't know those frame backpacks any other way.

Also, rubber CPS does not pressurize anything really. The Super Soaker CPS 2000 box reports the pressure as 26 PSI from what I know, which is far lower than most any other air pressure water gun. Even still, to use air pressure to get what the Super Soaker CPS 2000 does wouldn't take more than 80 PSI and the right design.

Big Bee, the owner of the Buzz Bee Toys line, told me in an email that all you would really need to make a water gun shoot 100+ feet is 150 - 200 PSI and good design practices. Pressure-rated schedule 40 pipe should be completely sufficient for this project - just make sure that the pressures you use are below 75% of the already conservative pressure rating.

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Post by frankenbike » Wed Jun 22, 2005 2:10 am

Originally posted by Doom@Jun 21 2005, 01:22 PM
I know you're talking about a frame backpack with a belt. I biked most of the C&O canal while wearing one. Carrying 25 pounds of water on a frame backpack without a belt would be damaging to your back. I suppose I don't know those frame backpacks any other way.
I'm back to thinking "enclosed backpack". Why? While it would be fun to look like a "Ghostbuster", people and especially police in Vegas are nervous about terrorists. A couple of big cylinders visible on my back with a lot of arcane tubes sticking out of them might give people the wrong impression.

Exposed, they'd have a nice intimidation factor under other conditions.
Also, rubber CPS does not pressurize anything really. The Super Soaker CPS 2000 box reports the pressure as 26 PSI from what I know, which is far lower than most any other air pressure water gun. Even still, to use air pressure to get what the Super Soaker CPS 2000 does wouldn't take more than 80 PSI and the right design.
I haven't taken one apart, but if the rubber CPS is contained by a plastic pressure container, that's where the pressure comes from. It has the design benefit of high pressure without having to worry about perfect sealing on every single part.

As for "the right design", well that's key, isn't it? But there aren't a lot of variables once you have pressure.
Big Bee, the owner of the Buzz Bee Toys line, told me in an email that all you would really need to make a water gun shoot 100+ feet is 150 - 200 PSI and good design practices. Pressure-rated schedule 40 pipe should be completely sufficient for this project - just make sure that the pressures you use are below 75% of the already conservative pressure rating.
I'd prefer to run no more than 50%. The rating drops as the temperature increases. Also, there are many more failure points than the tanks themselves to worry about. I don't really see a need to hit 100 feet, other than to say I could. 60 feet is both adequate and achievable by brute force alone, without any design finesse.

I have been adding a couple of design features in my hunt for hardware. I need a shutoff valve at the CO2 cannister, a pressure relief valve at the top of the tanks, and a water shutoff valve at the bottom.

I ordered the 3/8" pressure washer gun and 12" wand from Campbell-Hausfeld. That's a chunk of change. But it's the only one I could find and it looks cool.

With all the money this is going to cost (new estimate ~$150), I think I'll have to get further utility from it, like using it to wash the motorcycles and maybe the cars. They do make a soap attachment, and I could hook it up to the compressor to conserve CO2 ;)

Advantage over the hose: I can use the filtered water we have in the house which doesn't leave spots.

Another thing I've been thinking about is taking apart a "shower massage" head to see how it works. Be kind of fun to get a kind of "water machine gun" affect. I know people talked about it here, but I haven't seen any examples of anyone actually following through. Once you have the luxury of unlimited pressure, there's all sorts of things you can consider that would have been a waste when you have to pump the beast up.

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SSCBen
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Post by SSCBen » Wed Jun 22, 2005 3:13 am

I haven't taken one apart, but if the rubber CPS is contained by a plastic pressure container, that's where the pressure comes from. It has the design benefit of high pressure without having to worry about perfect sealing on every single part.
No, the rubber itself provides all of the power. I'm completely unsure of what Larami meant by the pressure on the water gun package. The water doesn't compress as far as we are concerned. It might have been some sort of nozzle pressure.

The three most important variables are pressure, nozzle size, and linear flow, the latter being the one people pay the least attention two.

As for my 100 foot range example, if you didn't know, I only meant to show what is overkill. ;)

frankenbike
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Post by frankenbike » Wed Jun 22, 2005 7:28 am

Originally posted by Doom@Jun 21 2005, 08:13 PM
No, the rubber itself provides all of the power. I'm completely unsure of what Larami meant by the pressure on the water gun package. The water doesn't compress as far as we are concerned.
There is such a thing as water pressure ;)

There is also a chance that the presumed 26psi pressure is based on some sort of average based on the expected user, instead of people pumping the heck out of it until the water pressure is much higher. Which is possibly why they redesigned them for lower pressure in subsequent models <_<

We'll know in a couple of weeks how this all works. Seems to me like you just can't go wrong with a lot of pressure, a lot of water and some way to stop it all from leaving the tank all at once, but when it does, it should leave in a convenient and lengthy stream.

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SSCBen
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Post by SSCBen » Wed Jun 22, 2005 3:12 pm

^ I know there can be water pressure, but for our purposes, water is incompressible. It would take thousands of PSI of pressure to pressurize water. We're not working with machinery that cuts with water you know.

Water pressure and air pressure are two different things. They did not design the system to use less pressure, they only made a system that ejects water via rubber - the rubber stretches and collapses to eject the stream. Simply put, there is no pressure!

Now that I remember when I bought my latex rubber tubing to make a few rubber CPS homemades, there was a pressure rating for each tube, which I believe was the pressure needed to cause the tube to expand. 26 PSI sounds reasonable for that. Because the water is essentially incompressible, any water pumped in will cause the tube to expand, given that it can be pumped in (if the rubber is too thick it will be hard).

I hope I cleared up that misconception. There isn't any pressurization going on in a rubber CPS system, so let's get that straight.

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Post by frankenbike » Wed Jun 22, 2005 7:22 pm

Originally posted by Doom@Jun 22 2005, 08:12 AM
Water pressure and air pressure are two different things. They did not design the system to use less pressure, they only made a system that ejects water via rubber - the rubber stretches and collapses to eject the stream. Simply put, there is no pressure!
If you take your garden hose outlet, and put a water pressure gauge on it, there is indeed pressure there.

As well, the rubber has a spring rate that is measure in PSI. This would be the number that is reflected in the water pressure when the rubber is compressed. You can put a water pressure meter on these devices if you want to actually take measurements. Just put a "T" in and install one of these. You can get water pressure gauges at any hardware store.

Water is compressible. Very small changes in compressed volume result in large changes of pressure. If you compress water alone, say with a screw and piston rather than some continuing force behind it, as soon as you allow the water to escape that pressure, a small amount will shoot out until the water and atmospheric pressure reach equilibrium. Most of the water will stay in the compression chamber, because the force compressing was static and not dynamic.
Now that I remember when I bought my latex rubber tubing to make a few rubber CPS homemades, there was a pressure rating for each tube, which I believe was the pressure needed to cause the tube to expand. 26 PSI sounds reasonable for that. Because the water is essentially incompressible, any water pumped in will cause the tube to expand, given that it can be pumped in (if the rubber is too thick it will be hard).
Assume the rubber is for all mathematical purposes, a spring (this is a reasonable assumption). Spring rate is usually measured in pounds per inch. That is to say, if the spring rate is 26 pounds per inch, it takes 26 pounds to compress that spring one inch. It takes 52 pounds to compress it two inches, it takes 78 pounds to compress it 3 inches and it takes 104 pounds to compress it 4 inches.

I'm uncertain what measurement is actually being used in the rubber expansion rating, but the properties appear to be additive just as with a linear coil spring.
I hope I cleared up that misconception. There isn't any pressurization going on in a rubber CPS system, so let's get that straight.
We must have some sort of disparity in terminology here. See above. If the CPS rubber takes a certain PSI to compress expand it, that is the water pressure you would have if you measured it with a gauge. The water pressure stored while it waits to be released is potential energy. It attained that pressure through kinetic energy during the process of pumping up the system. The potential is maintained until it is converted to kinetic energy.

The CPS is being employed as an energy storage device. It is a spring of sorts, with the combined properties of a spring and piston, that exerts force on the water. It's stored energy can be measured by the water pressure, but that measurement won't tell you how long that energy will be maintained.

For that matter, the same is true in compressed air systems. Instead of a more clearly mechanical spring, the air is being used as a spring. I've had motorcycles where I took the springs out of the forks, and just used pressurized air as the spring so I could vary the spring rate just by changing the pressure in the forks. Again, if you measure the water pressure, you get the same number as the energy stored in the air spring. In a compressed air system, the water itself becomes the piston, and the only disadvantage is that you have to maintain an orientation of the pressure vessel that keeps the water on the outlet side at all times, or air will escape instead of water.

If the CPS rubber is placed in a sealed air chamber, you can get the combined effects of the CPS spring rate, combined with an air spring rate as the air is compressed in the chamber. However, the chamber can be oriented any way you like as there would be no "air bubble". This is particularly convenient if you want a device to have a horizontal orientation.

A similar effect can be achieved with a spring and a piston, however a metal spring takes up more physical space when completely compressed. A piston and an air spring, however, would work pretty well.

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SSCBen
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Post by SSCBen » Wed Jun 22, 2005 8:27 pm

Interesting! You sure explained the water pressure thing well. I don't know too much about compressing water so I'll take it from you.

Spring CPS has been thought of before, in fact it's an extremely common idea. Same with the idea to use a rubber CPS with pressurized air on the outside. Neither idea has been tested, but I have my doubts on the rubber CPS with pressurized air on the outside (sounds like the very poor XPS modification). The spring idea would definetly be worth some thought, that is, if someone actually made it!

A year or two back I thought of making a small syringe type piston with a spring and a handle to pull the piston back (similar to spring-powered Nerf dart guns). The spring would have to be weaker so that it may be pulled, but it should make a good fast loading pistol!

You seem to be absolutely full of ideas, so please continue making homemade water guns after you finish this one! We need someone like you to help keep innovation alive.

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Post by frankenbike » Thu Jun 23, 2005 7:09 am

Originally posted by Doom@Jun 22 2005, 01:27 PM
Spring CPS has been thought of before, in fact it's an extremely common idea. Same with the idea to use a rubber CPS with pressurized air on the outside. Neither idea has been tested, but I have my doubts on the rubber CPS with pressurized air on the outside (sounds like the very poor XPS modification). The spring idea would definetly be worth some thought, that is, if someone actually made it!
Rubber CPS with pressurized air on the outside should work fine. Essentially, it would give a progressive spring effect so as you approach the elastic limits of the CPS, the energy stored is even greater. It would be useful to have to pumps for a system like that. One to transfer the bulk of the water and pressurize it, and a finer one that pumps less water but is easier to pump to compress it further along with the air. CPS plus 200psi of air at the back would give a massive burst of initial pressure. Design the pressure chamber right on the water side, and you can utilize the initial momentum of the water to improve the distance above what you would get from the pressure of the CPS and the air behind it alone.
A year or two back I thought of making a small syringe type piston with a spring and a handle to pull the piston back (similar to spring-powered Nerf dart guns). The spring would have to be weaker so that it may be pulled, but it should make a good fast loading pistol!
Several different solutions. An elbow/link arrangement that multiplies your leverage to load the spring so you can run a really high spring rate. You can pressurize it like a CPS with a similar spring rate (26 lbs per inch).

Or you can run a springless piston in a mechanical system similar to a semi-automatic rifle using CO2. You have an air side and a water side. You fill the water side by running a low pressure on the tank to get it to automatically fill when you release the trigger. Once the piston moves completely to the rear, a linkage shuts the feet from the water tank. Press the trigger, and it runs high pressure (really high pressure, like 400psi) to the piston. You can release the trigger and it would shut off the pressure and refill the water chamber. If you hold it down to the end, the piston would reach the end of its stroke and automatically close the valve that feeds the CO2 pressure side of the piston and once again reload the water chamber.

You can set this up to run "full auto" so it keeps cycling as long as you have the trigger held down.

When I talk about $200+ sport water guns for the adult market, this is the design I would expect to be dominant. That water would hit hard, it would hit for a short duration, and you'd better be wearing safety gear, because it'll hurt ;)
You seem to be absolutely full of ideas, so please continue making homemade water guns after you finish this one! We need someone like you to help keep innovation alive.
I'd like to make one of the above. But it's kind of involved and requires a lot of machine work. As well as R&D that includes: material science work, development of lubrication subsystems for reliability, and chamber design to take advantage mass momentum. For full auto use, there's a chance that building a resonant chamber might have a payoff.

Unfortunately, no one would want to play unless they had one too. And I'm not going into mass production.

I'm pretty sure the simple, portable pressure washer like device will be intimidating enough ;)

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SSCBen
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Post by SSCBen » Thu Jun 23, 2005 1:42 pm

Rubber CPS with pressurized air on the outside should work fine. Essentially, it would give a progressive spring effect so as you approach the elastic limits of the CPS, the energy stored is even greater. It would be useful to have to pumps for a system like that. One to transfer the bulk of the water and pressurize it, and a finer one that pumps less water but is easier to pump to compress it further along with the air. CPS plus 200psi of air at the back would give a massive burst of initial pressure. Design the pressure chamber right on the water side, and you can utilize the initial momentum of the water to improve the distance above what you would get from the pressure of the CPS and the air behind it alone.
I'm not saying that it won't work in theory... just that it would likely pop the rubber pressure chamber after a few shots. Every time I performed an XPS modification, the balloons in the pressure chamber popped, and I thought you were a bit familiar with a few modifications. ;)

I sure wouldn't squeeze a piece of pressurized LRT... there's better pressurization methods anyway!

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Post by frankenbike » Thu Jun 23, 2005 7:20 pm

Originally posted by Doom@Jun 23 2005, 06:42 AM
I'm not saying that it won't work in theory... just that it would likely pop the rubber pressure chamber after a few shots. Every time I performed an XPS modification, the balloons in the pressure chamber popped, and I thought you were a bit familiar with a few modifications. ;)
It's not the concept that's the problem there, it's the engineering ;)

Here's what I had in mind:

You have the homemade CPS system with the inflatable latex hose CPS. You figure out the maximum amount of water you can fill it with under normal (no pressure chamber) conditions before it bursts. Measure the dimensions that it is taking up at that point.

Make a pressure chamber that is exactly that size. For the sake of argument, let's say it'll fit in a 4 inch PVC tube 6 inches long.

Encase the CPS in the tube. Make sure the tube is airtight at both ends, so as the CPS inflates, the air pressure inside the tube outside the CPS increases. As the CPS inflates and takes up volume inside the tube, the air pressure outside the CPS increases. This will boost your fire power from the CPS.

The elasticity of the CPS doesn't change. The size of the chamber can't exceed the elastic capacity of the CPS.

The advantage this system would have over a simple APS is that it can be oriented in any position, and the pressure delivery as the added air pressure chamber depletes itself would be slightly higher since CPS pressurization of the fluid is more linear (APS is logarithmic, I believe).

Orientation isn't a small consideration. My CAPS system won't work for long if I try to fire while I'm laying down, or leaning too far forward.

Essentially, you get a combination of linear and logarithmic energy storage, so the initial burst would be immense and would hit hard.

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Post by SSCBen » Thu Jun 23, 2005 8:09 pm

As you said at iSoaker.com, you could add a divider to separate the air and the water in the CAP system, but the problem is pushing the divider back up. MrPukeOnYourHead used a dowel rod many years ago in a design like that, but that's not practical at all in a backpack!

You could make a system to use pressure to move the divider back, but that would waste air and likely make the water gun more complex in use.

I'm personally mostly interested in constant pressure - a logarithmic drop would be an improvement over the linear dropping of regular air pressure, but not much in my book. I still have my doubts on whether or not a piece of rubber tubing could handle outside pressure very well.

In other news, I've found that you can order fire hose nozzles from McMaster.com! Nozzle D (brass) with a 1" diameter and a 5/16" orifice would be an excellent, but expensive choice when looking for maximum performance. Because it is made of brass, you should not have trouble drilling a nozzle of a larger size in. If you are dissatisfied with your pressure washer nozzle, please give that nozzle a try!

You've sparked some interest in my homemade water gun creation and instead of using my saved money to replace my stole MP3 player, I'm planning a CAP design to address a few problems I have with my current homemades.

Are we the only ones participating in this discussion? :P

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