homemade cps system - simple pvc setup

Guides and discussions about building water blasters and other water warfare devices such as water balloon launchers.
frankenbike
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Post by frankenbike » Thu Jun 30, 2005 8:04 pm

Oh yea, as far as pressure sources, there's always the approach I'm working on. The large 20oz CO2 tanks with regulators favored by competitive paintball gun users. Start with 1000 PSI and enough air to propel 8 gallons of water regulated at 100 PSI.

I think you'd have to be able to get the water up to supersonic speeds for it to vaporize on exit. I don't even know if that's possible with compressed air or CO2. But it might be possible with liquid nitrogen propulsion. At that point, you've left soaker territory and moved on to the kind of power you get from firearms.

Which, incidentally, is another way you can carry a small package which generates huge pressures. I think you can pressurize 1 liter of volume to 10,000 PSI with a single 30-06 blank cartridge with full powder load.

Of course, ideas like that go on my "Pile of unacceptable ideas" along with the one that is basically a motorcycle engine cylinder powered by gasoline that can push a great volume of water at very, very high pressures. 1 pint of gas would let you pump out at least 30 gallons of water at >500 PSI. I was thinking, a cylinder off a 2 stroke, single cylinder, 500 cc bike would be about right ;)

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Aquarius
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Post by Aquarius » Thu Jun 30, 2005 10:29 pm

frankenbike wrote:I think you'd have to be able to get the water up to supersonic speeds for it to vaporize on exit.
If the process involved a sufficient transfer of heat, yes. One could concievably get the pressure high enough to solidify the water at standard temperature, probably not with a water gun though.

At any rate, water will not vaporize on exit unless one was shooting it into an environment with an ambient pressure of 9.869E-03 atmospheres or 0.145 psi (at standard temperature), essentially a vacuum. :oo:

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Post by isoaker » Fri Jul 01, 2005 8:46 am

As an aside, perhaps I shouldn't have used the term 'vaporize' upon exiting the nozzle at high pressures. As frakenbike noted, one of the major problems is air resistance. I keep getting images in my mind of really huge mist-shots with higher-pressure-based CAP systems. I wasn't aware that pressure washers can operate upwards of 1000 PSI. I still wonder, though, how much carbonation would occur if you're pressurizing water say using compressed CO2 at 150-300PSI? If the stream is carbonated, will the CO2 bubbles as they begin to form greatly disrupt the consistency of the stream, fragmenting it sooner than expected?

Then again, separating air from the water as in a divided CAP system or in a CPS-type system (that doesn't rely on air pressure), there would be no gas problem on the water side.

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frankenbike
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Post by frankenbike » Fri Jul 01, 2005 11:37 am

isoaker_com wrote: I still wonder, though, how much carbonation would occur if you're pressurizing water say using compressed CO2 at 150-300PSI? If the stream is carbonated, will the CO2 bubbles as they begin to form greatly disrupt the consistency of the stream, fragmenting it sooner than expected?


Now that is a good question I've wondered about a little myself. Especially since it's the principle pressure source I plan on using in my CAP system.

From what I understand, carbonation occurs when you dissolve CO2 in the water, and it wouldn't happen right away when you pressurize the system immediately after filling. But it could happen over time and would likely interfere with the stream flow. Especially if I'm running around with the water and CO2 mixing in the tank.

Butt...

When I was a kid my father would get seltzer delivered in those old style bottles you used to see in 3 Stooges shorts. I got yelled at for using one of those in a water fight. It was fairly close range, but you could hit someone with a pretty good stream of carbonated water.

Ultimately, if I were designing a commercial product, I'd set it up so I'd fill the tanks from a hose and separate the CO2 from the water with pistons. The only reason I'm not doing that on my system is that it's unlikely for the purpose I'm using this for that I'll have access to a hose.

The problem is that once the pistons are pushed down, a mechanism has to be set up to push the pistons back up. The pressure from a water hose would be perfect for that. Absent that, there would have to be some other mechanism employed like a pump to pressurize the bottom half of the system and it would have to be filled from the bottom.




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isoaker
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Post by isoaker » Fri Jul 01, 2005 12:22 pm

The problem is that once the pistons are pushed down, a mechanism has to be set up to push the pistons back up. The pressure from a water hose would be perfect for that. Absent that, there would have to be some other mechanism employed like a pump to pressurize the bottom half of the system and it would have to be filled from the bottom.


Somewhere (don't ask me to dig up the post), I recall you stating an idea along the lines of lowering the air-pressure side during a filling process. This would allow a handpump to be able to refill the liquid-side of a piston mechanism without needing to fight a rock-solid pump. Once the liquid was refilled, the air-pressure-side could then be re-pressurized to performance pressure.

On the other side, I do like the simplicity of the CPS-type chamber, though power is obviously limited by the nature of material the chamber is made of. Pressurized gas is just simpler to achieve greater force from than rubber or latex-based bladders.

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Post by Aquarius » Fri Jul 01, 2005 2:11 pm

I still wonder, though, how much carbonation would occur if you're pressurizing water say using compressed CO2 at 150-300PSI?


Not much, even if you used water just above the freezing point. Also, consider that the water you're using already contains some measure of dissolved gas that isn't prone to escaping while under pressure.

If the stream is carbonated, will the CO2 bubbles as they begin to form greatly disrupt the consistency of the stream, fragmenting it sooner than expected?


Probably, but I'm the type that would fill something with Mountain Dew just to be sure.

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Post by frankenbike » Fri Jul 01, 2005 4:18 pm

isoaker_com wrote:Somewhere (don't ask me to dig up the post), I recall you stating an idea along the lines of lowering the air-pressure side during a filling process. This would allow a handpump to be able to refill the liquid-side of a piston mechanism without needing to fight a rock-solid pump. Once the liquid was refilled, the air-pressure-side could then be re-pressurized to performance pressure.


Yeah, you could do that too. I'm thinking of my "big pressurized tank" model I'm building with 3 13" long 4" diameter pipes, and pressurizing the whole thing. If you're working with a limited capacity chamber, it's a lot more practical to do it that way, but pumping 2 gallons with a hand pump would get very tiring and you'd get soaked while everyone attacked you during the 20 minutes you pumped the water into the system in revenge for a non-stop, 2 gallon water artillery onslaught ;)

On the other side, I do like the simplicity of the CPS-type chamber, though power is obviously limited by the nature of material the chamber is made of. Pressurized gas is just simpler to achieve greater force from than rubber or latex-based bladders.


I think I suggested that you could combine the two concepts by putting the CPS in a sealed chamber. As the CPS bladder inflates, it increases the pressure in the chamber like an APS system. You could also add additional pressure on top of that, and if the bladder were constrained on both ends or had some sort of "end stop" attached at one end, it wouldn't be able to invert.

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Post by wetmonkey442 » Fri Jul 01, 2005 7:48 pm

Hey guys...haven't been here much lately. I haven't really thought much about what the last few posts have been about, so pardon the change of subject, but I have an idea for a possible CPS homemade.

I've been experimenting with different homemade designs, and CPS technology is kind of weak in comparison. However, while perusing the items at Lowes the other day, I stumbled across the pip cleaning section. This is the section with all of the drain cleaners, and de-clogging rods that are supposed to make your pipes flow like new. On the shelf, sitting besides an industrial size can of Draino, I noticed a curious thing. An expandable latex tube pipe cleaner. The basic premise of this is to take, in essense, a cyndrical CPS chamber, shove it down your sink drain, and inflate one end with water, so it expands. As it expands, it forces all the gunk and grime away from the pipe, and a little hole in the end shoots water at a pretty high velocity through your pipe cleaning it.

However, I saw the potential for a CPS latex tubing. Not everybody has the capability or the desire to purchase latex tubing from an online source such as McMaster.com, and this misght be the answer to a cheap quick CPS homade. Simple melt the rubber at the tip to close off the tiny hole, and attach it to your gun. The end has a metal male threaded attachment already, making the seal super strong. I believe it would work, though I have not tested it yet.

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Aquarius
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Post by Aquarius » Fri Jul 01, 2005 8:13 pm

wetmonkey442 wrote:On the shelf, sitting besides an industrial size can of Draino, I noticed a curious thing. An expandable latex tube pipe cleaner. The basic premise of this is to take, in essense, a cyndrical CPS chamber, shove it down your sink drain, and inflate one end with water, so it expands. As it expands, it forces all the gunk and grime away from the pipe, and a little hole in the end shoots water at a pretty high velocity through your pipe cleaning it.

They totally massacre clogs. If you could get one to expand enough to make usuable as a CPS chamber, you're doing well. From the looks of them they're pretty heavy duty.

There is another option for a CPS type chamber I discovered today. As I understand they're typically made to small volumes, not anywhere near what you'd need. Larger one's would have to be fabricated. They're called accordion bladders.

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Post by isoaker » Sat Jul 02, 2005 9:22 am

-------------------------------------------------

Back to topic, while the homemade CPS has more limitations, it's definitely an area worth exploring for those who want to tinker and accept responsibility for their experiments. I definitely enjoy reading and discussing these concepts. Of course, for day-to-day water fights, I still prefer promoting standard stock blasters as they are still the most easily accessible for the widest number of people.

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tech23
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Post by tech23 » Sat Jul 02, 2005 10:38 pm

Has anyone drawn a diagram on how a CAP system works? I just need a basic drawing, none of the extra stuff. If I knew how they worked I might be able to design a pretty good one (and make it, of course).
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frankenbike
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Post by frankenbike » Sun Jul 03, 2005 3:40 am

A CAP system is pretty simple in concept.

Two designs:

1. A moderately large tank with pressure in excess of what you're going to use (say 200psi), an adjustable pressure regulator (say, set to 100psi), a tube leading to the firing chamber filled with water, and a valve that you open to introduce the pressure to the firing chamber which pushes the water out of it with continuous pressure that doesn't decline until the pressure in you large tank drops below the pressure you set with the regulator.

So you'd pump water into the firing chamber, which would be easier if you have a compression release valve, open your air valve and you get a constantly pressurized stream until the water runs out of the firing chamber.

2. You pressurize your whole reservoir, again with a larger air tank. You have something like the typical ball valve as your trigger which holds the water in the reservoir back, and you let loose when you open the valve.

You can pressurize your air tank in advance with a compressor. Or a tire pump. Or as I'm planning, skip the air tank and put a moderately large CO2 or HPA (high pressure air) tank (a 20 oz CO2 tank a little larger than a tall boy beer can will power about 33 liters of water at 100psi) with a pressure regulator (preferably with a pressure gauge that's on the output side of the regulator). The latter is expensive, but while your friends are pumping away, you're blasting them ;)

Is there anywhere that people can upload drawings on this forum?

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Post by isoaker » Sun Jul 03, 2005 7:05 am

Is there anywhere that people can upload drawings on this forum?

If you've got a drawing that you want pushed up, email it to me and I'll put it onto the iSoaker.com server. I'll then send you a link to where the image is housed so you can include it in your post. While I'd like to, I don't permit free FTP access for fear of abuse for non-soaker images or huge image files (iSoaker.com's server has a lot of space, but then again, iSoaker.com's site takes up a lot of space :goofy: )

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frankenbike
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Post by frankenbike » Mon Jul 04, 2005 7:17 pm

I've whipped out a couple of illustrations which cover at least a couple of the CAP concepts we've discussed. I hope these help a little.

Image


Image

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Post by isoaker » Mon Jul 04, 2005 8:02 pm

Clean, simple, yet worth more than 1000 word diagrams. Nice! That should help clarify things for those unsure of some of the things being discussed.

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frankenbike
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Post by frankenbike » Tue Jul 05, 2005 12:06 am

There are a lot of different ways you can arrange the pieces, use smaller tanks, etc. I just tried to make an explanatory drawing that read a little better as a kind of schematic. For materials, I wouldn't recommend PVC as the air tank if you're running over 150psi, even if it's sch80. I'd get an inexpensive fire extinguisher and use metal parts on it.

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Post by tech23 » Tue Jul 05, 2005 1:11 pm

Really? I got some sch40 1/2" pipe that has a rating of 600 psi at 73 degress. I guess it's the joints that are the problem.

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Post by SSCBen » Tue Jul 05, 2005 2:38 pm

No, he means larger diameters of PVC. Once you get over about 1 1/2", it's harder to find pressure-rated PVC. Pressure-rated PVC is just about guaranteed to be safe given the pressure used is below the pressure-rating. The fitting should be pressure-rated as well.

I've got a load of 850 PSI sch. 80 1/2" pipe - but I use it for Nerf barrels. :laugh:

Higher schedules of PVC are thicker and therefore hold more pressure, but many times you won't find a pressure rating on those on larger diameters as well.

The only real way to be sure that you are being safe is to use pressure-rated pipe, whether it is metal or plastic. As it turns out, it probably is easier to find a fire extinguisher than large diameter pressure-rated PVC pipe.

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Post by frankenbike » Tue Jul 05, 2005 2:52 pm

Couple of caveats about that, though. First of all, all the sch40 and sch80 PVC I've seen has a label on it that says something like "Not to be used for air pressure".

But the reason I wouldn't recommend building a high pressure tank out of PVC or ABS is what you say. The joints, caps, fittings, etc., are all dependent on your expertise and attention to detail.

And while 1/2" sch40 might be rated at 600psi, that isn't going to give you much of an air supply for a CAP system. 3 or 4 inch sch40 is rated more like 325psi at 72 degrees, and it drops significantly at higher temperatures. A typical sunny day for a weather fight is going to be 80-90 weatherman degrees (AKA "in the shade"). In direct sunlight, that temperature is even higher. You can expect some cooling effect from water, but the air tank not only won't have any cooling effect because there's generally no water in it, it will actually heat up when you put compressed air into it.

In engineering, designs for things like pressure tanks are tested to destruction. Mis-estimations of durability can be catastrophic.

If I were seriously considering compressing a system to pressures over 1/3 of its rating, I'd probably plan on building one for testing to destruction, as well as building a sufficiently strong containment chamber. Then increase pressure incrementally with a video camera on the pressure gauge until it exploded.

Then I'd repeat this test, but this time with a heater and thermometer, to get the chamber temperature up to 125 degrees, a pretty fair "in the sun" temperature to use as a maximum baseline.

While 100-150psi is certainly dangerous in the case of a pressure vessel failure, 300psi (for example) can launch sharp PVC and ABS shrapnel at over 100mph. That's not just "put an eye out" dangerous, that's "stupid Darwin Awards death headline on CNN" dangerous.

Consider that the cost of a PVC tank might be up in the $7-10 range, and you can get a fire extinguisher with aluminum pressure cylinder for $12 new. You'd have to set it up for a permanent pressure outlet, but you should expect some diligent work if you're going to make some sort of high pressure system anyway. If you don't exceed the system's pressure specs, the worst that can happen if you're careless is that it turns into a rocket and kills someone that way. But that can happen no matter how you design a pressure tank, and at least it should be pretty easy to secure something like that with a big hose clamp or two.

Of course, if you can find a cheap CO2 fire extinguisher, you're in fat city. Those can hold up to 1000psi and you can use the CO2 to make a seltzer CAP system. But typically, they're over $100.

Dry chemical fire extinguishers with aluminum bodies I think are typically charged at 100-200psi, but can take much higher pressures. I'd have to do more research to find out the actual upper limits.

edit: it appears that 200psi is the strongly recommended upper limit for typical household dry extinguishers.




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Post by NiborDude » Tue Jul 05, 2005 7:28 pm

I think the second version could be turned into a turret and be used for base defense. The barrel could be easily mounted. I like the concept.
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