Clean and Simple Air-Canisters - Not just a design, the real thing

Guides and discussions about building water blasters and other water warfare devices such as water balloon launchers.
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WaterWolf
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Post by WaterWolf » Fri Jul 27, 2007 2:31 pm

Back from the abyss, I have several items to contribute to the water-warfare community, these new systems and weapons will be slowly dropped one by one into the forums, to allow proper digestion by the people here.

IMPORTANT, READ THIS FIRST!

Note that you, the builder and user of any of these assume full responsibility for your Custom built Water-Weaponry and what happens with them. Work safely. Play safely. Remember, all of these are powerful and anybody wielding one needs to be responsible with them. Treat it with respect, never over charge their pressure tanks. Never fire them at somebody’s head - This is especially necessary for the water balloon launchers. Never fire anything but clean water/water-balloons. In the hands of an experienced, responsible player these can be safe and fun to build - highly useful in giving your team the technological edge in Water-Warfare.

Now, on to our regularly scheduled content.


This is a piece that I designed as an add-on to water balloon launchers, Cannons or most any air powered homemade and would be highly necessary if the equipment is intended for use in the middle of fast moving combat.

The premiss of it is fairly simple, a large container of high pressure air, feeds through an air-regulator and out to the pressure chamber of the launcher after every shot. This would allow for balloons to be fired as quickly as they are pushed down the barrel and cut the reload-time of a launcher down a speed at-which they would be more practical in the recently developed "Tactical Theory" strategies of water warfare.

The air canisters can be used like batteries to power most homemade weapons. Once a canister is drained, plug in a second and its ready to go. Recharging them however, requires an air-compressor or bike-pump that can achieve the fairly high Pounds-per-Square-Inch necessary to allow for multiple shots. But these devices are often not too expensive or hard to find.
In order to prevent loss of air between water balloon launcher shots, I also have a homemade air FLOW regulator (different than a pressure regulator), which allows more control over the air as it moves between the canister and the pressure-chamber.

Image
Air-Canister V1.0 "before" picture.

The current version of air-canister is made out of a 3-liter soda bottle. I tested it for durability by first charging the bottle to 140 PSI (This a little ways beyond what I would suggest using them at), then proceeded to abuse it as strongly as possible (from a safe distance). The first test involved throwing it several times at a boulder (no effect), after which I took cover behind a barrel and began pelting it with a barrage of stones, each significantly bigger than my fist. Basically putting more sudden and hard impacts on it than it would ever have to withstand in a water-warfare battlefield. Eight hits later, it finally ruptured after being smashed dead-on with a particularly sharp edged rock. The result was an explosion as the air that sent plastic derbies up to thirty feet away. Interestingly enough though, the shrapnel I had worried the most about (the metal adapter used to plug it into the air compressor) had not moved more than a few feet from ground zero.

Even though this test demonstrated a surprising level of durability, in an end model of the bottle air-canister, I would have a chicken wire cage or cloth sock surrounding it, to prevent any shrapnel from flying out.

Image
Air-Canister V1.0 "after" picture.

I'm thinking of trying to use a different container for the body, such as a mini helium tank, which I could buy an adapter for to hook it up to standard air-hose connectors. With an easy way to hook them up, the steel canisters would be better, since they can take a greater volume of air at a higher PSI without bursting and are tough enough that it would be very difficult to damage one of them without some heavy tools and plenty of repeated smashing.

I can fit three bottles in a standard backpack. How many shots you get per canister depends greatly on what PSI you set the air-regulator too and how big your PC is.

I haven't tested this idea yet, but these canisters should be easy to link together with a few Tees.

Another advantage of a steel canister is that its simply a cleaner set up than multiple bottles linked together. The mini helium tank I found doesn't seem to be too heavy either, its about 8 pounds and can carry six times the amount of air in sheer volume. My only concern with it is that it might stick out to far from my back, but I should be able to get the part to test it quite soon.

I have built several of these "Air Battaries" and intend to battle test them on my new CAP cannon at our team's next meeting.

Construction is simple and fast, but there are a few key items that, if followed correctly, allow it to contain air for many many hours without much (if any) noticeable loss of pressure. I will discuss these in my following guide on how to build them.
The Maple-Mountain-Marines.

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-B.D.

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isoaker
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Post by isoaker » Fri Jul 27, 2007 8:55 pm

Interesting idea, though I'm not sure how much I'd trust pressurizing pop-bottles to higher pressures. More testing info and other findings would definitely be appreciated. I'd definitely feel better if these bottles were in a wire mesh just in case of rupture; not all pop-bottles are made the same way and I wouldn't want to hear about an accident due to an unseen defect in a bottle used.

Of course, if it works as good as planned, sounds really cool.

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WaterWolf
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Post by WaterWolf » Fri Jul 27, 2007 9:20 pm

I'm not sure if you read the entire post properly, I said that:
"In an end model of the bottle air-canister, I would have a chicken wire cage or cloth sock surrounding it, to prevent any shrapnel from flying out."

What kinds of findings are you asking for? More durability tests?
I did conduct a second test, during which I fired hollow tip pellets at it, from a fairly high FPS BB-rifle. Surprisingly, the bottle did not explode, even after many direct hits.

I would personally suggest not using these at pressures much higher than 140 PSI. They should be able to stand much greater levels, but I like to keep it a significant distance from its breaking point, for the obvious safety reasons.

That is one of the reasons I stated that I would prefer to use steel canisters instead, they are extremely tough and difficult to puncture. But these soda bottles show a surprising level of strength to me.
The Maple-Mountain-Marines.

Terrifying, but oddly refreshing.
-B.D.

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Post by isoaker » Fri Jul 27, 2007 9:28 pm

Oh, I read the part about the chicken wire about the canister and, of course, about your rock throwing at the pressurized chamber. Thing is, as far as I can tell, you have only tested one of these. I'd want to see a few more bottles tested as well as how it behaves in a mesh. If tests on a reinforced pop-bottle prove decent and the pressure it supplies good enough for your blaster/launcher, it sounds rather promising.

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WaterWolf
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Post by WaterWolf » Fri Jul 27, 2007 9:44 pm

Two tests actually. And I will do more using various reinforcements.
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Post by cobralex297 » Fri Jul 27, 2007 9:49 pm

The idea of using chickenwire to avoid and contain shrapnel is a novel one. I'd be quite interested to see images and possibly statistics detailing results of it's addition.

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Post by SSCBen » Sat Jul 28, 2007 9:17 am

Soda bottles are not serious pressure vessels. They are designed to hold a certain level of pressure, but definitely is not over 100 PSI. I've seen them pop at as "low" as 80 PSI. Now while their shrapnel is less than lethal, it still is not wanted and I would rather not feel I need to add a "chicken wire" cage around the bottle. I've read on spud gun forums that some sort of mesh covering is somewhat effective, but in a serious failure the mesh won't help.

My suggestion would be HPA (high pressure air) tanks available from Paintball and hobby stores. These tanks hold 3000 PSI, are relatively cheap, and can be regulated down as low as you'd want it. Of course, they're not as cheap as this is, but if you want cheap, safe, and reliable, I would suggest a PVC tank with a threaded ball valve. Definitely avoid 3 liter bottles. The fact that it exploded after 8 hits isn't a sign of durability. I've seen what it takes to make a PVC tank fail and it certainly is a lot more than 8 hits from sharp rocks.

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Post by WaterWolf » Sat Jul 28, 2007 11:41 am

The problem with a PVC solution is that it weighs a lot more, is difficult to get air-tight and more expensive. Plus, should it fail, the shrapnel would be much more dangerous.

As for paint-ball tanks, the volume is simply too low and they ARE quite expensive.
You would also need an extremely powerful air-compressor to pump in enough air to make it worthwhile and I'm not even sure if I could find the parts to adapt from their threading to a standard air-hose.
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Post by SSCBen » Sat Jul 28, 2007 12:50 pm

PVC is hard to get air tight? Last time I checked, plastic bottles were hard to seal. PVC is very easily air tight.

You definitely are overemphasizing the dangers of PVC failure if you choose plastic bottles for "safety." Let's say PVC fails 0.0001% of the time due to being mistreated and that is guaranteed to be fatal (and it's not likely to be fatal at all, I have seen a failure before). Getting a serious failure on that level will take perhaps two or three times the pressure rating of the pipe. That's certainly a lot better than the near guaranteed failure rate of a plastic bottle at pressures over 100 PSI. What's more dangerous? Definitely the plastic bottle.

I understand that weight might be a problem with PVC, though, I wouldn't imagine a 3 liter PVC tank would weigh more than 5 pounds. The answer to weight is not a thinner material, but a material that is strong enough to hold pressure for less weight. You mentioned steel tanks... if you want heavy, that'd be it. Aluminum is what HPA tanks are made of from what I know. Strong, lightweight, but not the cheapest.

The HPA tanks definitely contain more air than a three liter bottle. They might be smaller in physical size, but the 3000 PSI they hold is very significant. They probably contain somewhere on the order of 5 to 10 times as much air. And they're relatively cheap. You fill them at the store, for pennies last time I checked (at least locally). They're the way to go.

Thought I'd clear all that up... I really do not want to see someone getting hurt from pressurizing a soda bottle to over 100 PSI. That is beyond their pressure rating and as you demonstrated, can create a failure.




Edited By Ben_ on 1185645140

WaterWolf
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Post by WaterWolf » Sat Jul 28, 2007 6:51 pm

Fine. Use whatever canister you want. The point is the system of air-batteries, which could allow certain homemades to become much more battle-practical on the field.

In future, I would prefer it if you would send constructive comments to my topics.
It seems like what I'm more often receiving from you are direct criticisms on my designs and hints that your ideas are better.

I do appreciate the genius of some of your systems, but more helpful comments on mine would be appreciated.




Edited By WaterWolf on 1185672996
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Post by SSCBen » Sat Jul 28, 2007 9:25 pm

Don't get so annoyed. I'm offering certainly constructive suggestions. These suggestions come from experience and a good general knowledge. Some people seem to take my suggestions as some sort of insult, but what I say comes from experience. I am only trying to help you. I suppose some people want to make their idea and only their idea. A lot of people don't choose to believe my experience and that's okay. With that being said, I am concerned about the safety of your tank system and I offered suggestions to improve the safety of your idea. No offense was intended and I sincerely apologize if you were insulted by my suggestions.

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Post by isoaker » Sun Jul 29, 2007 6:37 am

If this is to be believed, the plastic PET bottles can withstand up to 250 PSI. I'm still looking around to see if anyone else reports something differently. Of course, bottles are known to rupture at lower pressures than that, but it is interesting that it got a rating that high.

More info on PET (Polyethylene terephthalate)

More info on various plastics

Is this true? "Indeed, carbonated soft drinks can generate pressure inside the bottle reaching up to 6 bar (125 PSI)."

This report done in 1997 by the University of Nottingham (PDF file) entitled Potential Hazards from carbonated drinks bottles rates these bottles and suggests they tend to fail around 150psi-200psi.

Things I never knew about pop/soda bottles...

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Post by forestfighter7 » Sun Jul 29, 2007 10:59 am

Wow! This is really cool. Perhaps I'll try it sometime.
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Post by isoaker » Sun Jul 29, 2007 11:04 am

I should note that in the first link I sent, another one doing tests had their bottle fail at 125psi. Considering it all, seems like these sort of bottles have a broad range of durability, likely depending on whether or not there were defects in the manufacturing process. How much pressure would you need (the lowest amount) in order for your blaster/launcher to behave the way you want it to? Would you be able to achieve good operations at pressures around ~125psi per bottle?

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WaterWolf
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Post by WaterWolf » Sun Jul 29, 2007 11:48 am

Yes, and though I hadn't seen that particular article, that is the pressure that I had been going to suggest people should charge theirs to. 130 would be the maximum I would want to use them at.
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Post by SSCBen » Sun Jul 29, 2007 1:34 pm

There's a big difference between burst pressure where the bottle can be put under shock and the pressure rating. From what I've read, the "burst" pressure of PVC typically is more than twice the pressure rating to make the ratings as conservative as possible. The burst pressures listed for soda bottles have to be similarly reduced. I have done my own tests. One bottle exploded at a mere 85 PSI, with no visible damage or shock applied. Others survived the full 150 PSI my compressor can output. Some bottles definitely are duds when it comes to holding pressure.

You also have to take into account temperature. Pressure de-rating charts put Polyethylene pipe at 90% strength at 80 deg. F, a perfectly normal water fight temperature. 90% isn't bad, but you have to take that into account as well.

"Shock burst" pressure ratings are what we are looking for, and it would be best to use more conservative pressures ratings than the known burst pressures. How safe would you feel a soda bottle is if it were pressurized to 120 PSI and you fell on it? That happens very often in water fights and it's what I see as a very real and very dangerous possibility if these air storage tanks are used. Heck, the website iSoaker links to even states "Never go near a pressurized bottle." Pressurized soda bottles burst far too easily.

Now, believe me on this because I'm argued before that a lot of "safety" concerns are nothing more than alarmist rants. If there was anything that is actually dangerous, using soda bottles at over 100 PSI is.

If you insist on using soda bottles, use a good strong mesh at the very least and cover both ends. Seal the mesh over the bottle more permanently by melting it or something. Essentially make the mesh take the impact instead of you or others. Some sort of foam over the mesh would also be a good idea in my opinion.

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