Concept: Air Wiz A10

Water blaster concepts and dream designs for water guns and related equipment.
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HBWW
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Concept: Air Wiz A10

Postby HBWW » Sun Mar 23, 2014 5:47 pm

Pumpless, pre-pressurized systems for launching liquids [url="http://science.howstuffworks.com/flamethrower3.htm"]have been around for a long time[/url]. They are essentially giant pressurized reservoirs powered by a regulator and high pressure tank holding some sort of gas such as CO2 or high pressure air. (Thousands of PSI.) This is essentially the same concept as the [url="http://www.sscentral.org/homemade/supercap.html"]SuperCAP[/url]. The problem with this traditional design however, is that you can't refill the water without venting and wasting a lot of air. Cleaner separation of the pressure source and water source are needed for versatility.

Here's my take on that problem. This design still has a problem: shot time. The maximum shot time is dictated by the regulator setting and by the size of the pressure chamber. Have a look.

AirWiz.png
AirWiz.png (23.87 KiB) Viewed 1418 times


Operation is a bit involved. Once hooked to your water and air source, press the trigger highlighted in blue to blast. To recharge the water chamber, open the orange valve and the air will vent to the WBL chamber. (Which can be charged directly using the green valve) To get the main pressure chamber completely empty, you'll need to vent it directly with the yellow valve. Finally, the trigger in front, highlighted purple, launches the balloon.

When venting, the push spring will automatically refill the pressure chamber. Of course, this leads to a problem of priming the internals without wasting air, where I haven't integrated a solution to the design yet. However, the problem seems easily solved by attaching a water pump along the water source line and priming the internals that way.

Overall, it's a convoluted and probably unworkable design. Realistically speaking, the traditional regulator to giant backpack reservoir solution is much easier to build. The air exhaust problem can be solved by attaching part of the backpack to a WBL, but it can only be used without wasting air when all water is gone from the backpack. By venting/wasting less air a a time, a WBL becomes more workable.

Of course, there's a whole separate discussion on whether anything that would require a regulator should ever be allowed in water wars anyway. Still, it's a fun concept to explore, except when thinking of all the money that could be burned to such a project.

Regardless, some design/concept critiques from our in-house experts would be nice to hear from. Unfortunately, it doesn't seem like the air exhaust problem is possible to resolve, but it seems like most pneumatic systems have some degree of air waste anyway. (At least, if those air hisses I hear are any indication of it.)

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DX
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Re: Concept: Air Wiz A10

Postby DX » Sun Mar 23, 2014 6:24 pm

I don't think there's any legal problems with the design, but in order to power a WBL, the main PC would need to be huge and not PVC. High pressure alone is not enough to run a WBL, it requires high air volume, too. A suitable pressure vessel would probably need to be made of metal and if not expensive, then very heavy. If it sits on top, that thing would be insanely unwieldy. You'd also need a way to replace the piston when it warps or the seal otherwise wears out, I don't know how that would work if using a very high pressure chamber.
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Re: Concept: Air Wiz A10

Postby HBWW » Sun Mar 23, 2014 6:37 pm

There's a few things I should've clarified, the main one being that this is more of a concept than a design, one that assumes very high budget and manufacturing capabilities.

The WBL is intended to be lower caliber, which should allow it to work with lower air volumes. It's a fine line to balance, since high pressure at low volume requires fast air release, which requires durable munitions to handle, yet are still able to burst on impact without being a safety hazard.

I do need to look into how to deal with the piston cup warping issue. Making them replaceable is usually not difficult, just put a female adapter at the end of the pipe and a set of reducing bushings. Of course, that setup won't give enough strength for the spring and the general stress the system is under. I don't know how much of this system could work with PVC; placing anything under a regulator means you really need a foolproof means of pressure relief if the regulator does anything funny. With a full metal system and higher pressure, you could setup a huge nozzle that empties the tank in a very short time.

There is also another issue I'm missing: I'm not sure how quickly a regulator can work. This design assumes near-instant air-filling of the chamber, which may also be a problem.

I guess it's probably better to deal with a large, nonrefillable backpack instead, but the only way to get the air needed is at a paintball field. Some of those machines can pack up a ~1L 3500 PSI tank pretty quickly.

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Re: Concept: Air Wiz A10

Postby SSCBen » Tue Apr 08, 2014 10:09 pm

This is a great idea, CA99. As you note, the implementation could be done more cleanly. Back in 2009 I started making plans for a water gun with the same overarching goal, so I'll share what I found. (This was never built, in part due to a lack of time, but also because I recall the valves needed were too expensive for me at the time.)

I don't remember all of the details, but here's the pneumatic circuit and my attempt to decode how it works 5 years after drawing it:

Image

This uses pneumatic circuit symbols, and some of them appear to be non-standard. The rectangles are complex valves. The flow paths through the valves are represented by the arrows. When the valve on the left is pressed (the button on top means it's actuated by hand), you can replace the bottom square with the top square. The flow paths will change. The valve on the right is similar, except that it's actuated by compressed gas from the left side of the piston. There's a needle valve on the feed to the actuator to add some delay for that.

The top is an pneumatic cylinder, which is something like this:

Image

Basically, when you pressurize the left side, the piston and rod moves to the right, etc. The rod will be attached to a piston pushing water with the standard check valve setup. The water chamber is not in the drawing I have, unfortunately. Essentially, the circuit here shows a way to automate a piston pumper with a separate reservoir.

If that didn't confuse you enough, I'll try to explain the circuit's operation.

The circuit actuates a piston that pushes water out of the nozzle or pulls it in to the PC. In mode 1 (shown in the drawing), the compressed gas source (the triangle; by "compressed gas source" I mean some sort of regulated gas system) leads to a plug (the x). The piston will be positioned to the right, such that water has been pulled into the PC. When the button/trigger is pushed, mode 2 begins. The left side of the pneumatic cylinder is exhausted to the atmosphere. The compressed gas source leads directly to the right side of the piston, pushing the piston to the left and thus firing water from the PC. When the trigger is released, mode 1 starts again. The left side of the pneumatic cylinder starts to fill with gas from the right side. At a certain point, the right valve is tripped by the pressure actuated switch (the needle valve controls the delay) and the right side is exhausted to the atmosphere (the dot means leads to the open air). This allows the left side to move the piston fully to the right.

As for specific parts, I have a spreadsheet that lists the following valves: Clippard's MNV-1, Clippard's MMA-41NAS, and Clippard's FV-5P. I'm not sure if these valves have high enough flow rates, but I imagine they do.

One problem with this design, that you are aware of, is the required check valve in the nozzle. This'll add a lot of turbulence to the flow. I think using something like a lightweight ball kept in place with a small elastic band as a check valve would be one way to reduce the turbulence.

Another problem is tap shots. I'm not entirely sure if they'll waste a ton of air or what. I figure getting tap shots to work well might require getting the needle valve timing just right and/or modifying the design a bit. I did try to make this design avoid wasting air if possible, which is why the air leftover after pushing water out the nozzle is used to refill the chamber.

I hope all of this isn't too confusing. I remember being very confused when I drew up this design myself, but I think I understand it now.

CA99 wrote:There is also another issue I'm missing: I'm not sure how quickly a regulator can work. This design assumes near-instant air-filling of the chamber, which may also be a problem.


Most regulators list a flow rate that you can use to get a rough estimate of the fill time.

To do this with good accuracy would require some more complicated math. For those interested in this route, I can suggest a few books. The Analysis and Design of Pneumatic Systems is a pretty good book on the subject, though I'd use the ISO valve equations from a book like Pneumatic Drives.

(I made this post in a rush, so forgive any egregious writing errors.)

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Re: Concept: Air Wiz A10

Postby marauder » Wed Apr 09, 2014 8:26 am

If it wasn't $60 I'd probably buy the book as I'm pretty interested in this subject.
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Re: Concept: Air Wiz A10

Postby SSCBen » Fri Apr 11, 2014 7:25 pm

marauder wrote:If it wasn't $60 I'd probably buy the book as I'm pretty interested in this subject.


I'm not sure that book is such a great introduction, as a lot of the methods in it are obsolete now, but it is comprehensive and has a good section on regulators. I bought mine perhaps 5 or 6 years ago used for about $20, as I recall. The other book, Pneumatic Drives, uses more current methods but does not cover many of the same topics. Incidentally, while Pneumatic Drives is much more expensive in book form, my undergrad university let me download it as a pdf for free.

[rant]

Unfortunately, I am not aware of what a great introduction to the subject would be, which is a shame. There is a lot of misleading, false, and confusing information, terminology, and practices in pneumatic systems. As an example, the "flow rates" you see listed for valves and other components are completely ambiguous. I discussed this in a blog post on my old Nerf blog a while back. I've learned a few things from this: 1) always ask a valve manufacturer how they calculate their flow rates and 2) check what they claim against your own tests.

Other confusing points: "choked flow" actually means choked velocity (many textbooks by university professors get this wrong!) because the flow rate can still increase, Cv is a way of measuring the flow capacity of a valve rather than a thermodynamic quantity, the critical pressure ratio is often assumed to be 0.524 (which comes from some very old theory) when in reality it's usually half that or less, etc.

[/rant]

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Re: Concept: Air Wiz A10

Postby HBWW » Fri Apr 11, 2014 7:57 pm

$60 is noting compared to the cost of what you have to shell out for this kind of equipment. That said, I pick my textbooks from... certain sources lol.

Interesting design, Ben. I've tried working out in my head different ways to drive a pump with air, although what I had in mind was a small pump hooked to a pressure chamber.

Pneumatic circuit drawings aren't doing much good for me trying to visualize what these things actually look like, but the gist of what your design is doing makes sense.

Anyway, looks like there's no way to do this without wasting air. We can store large amounts of pressurized air, but not so much for water. Perhaps the HPA/regulator/backpack is still the most practical way to do this; I don't think that design has changed for well more than a century. It's very simple and very effective.

HPA just happens to be the answer to WBL practicality as well as high performance, pumpless water cannons, but we have a unique problem there of requiring slower air release. Anyway, it's clear that there's a lot we can do with HPA in water blasting equipment, and I think if WW was ever popularized on a large scale, I have no doubt that that's where things would be already, for better or for worse. (But just imaging if we were all running around with some 500x, self-pumping riot cannons on our backs at community wars, haha.)

And while HPA in general is expensive, you can still pump it yourself. Just need a pump and some filters for the moisture. http://www.amazon.com/Benjamin-Discover ... B001BR6SCU I'm not sure if there's a better solution there. It seems that lower pressure air requires too much volume to be useful, and everything else relies on some odd form of gas. (CO2 or green gas.)

If we really mean it when we say "anything goes" in community wars, I'm definitely tempted to experiment with HPA-powered homemades and WBL's if I ever have the funds for it. Perhaps I spoke too soon though. :goofy:

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Re: Concept: Air Wiz A10

Postby SSCBen » Fri Apr 11, 2014 10:48 pm

CA99 wrote:Anyway, looks like there's no way to do this without wasting air. We can store large amounts of pressurized air, but not so much for water. Perhaps the HPA/regulator/backpack is still the most practical way to do this; I don't think that design has changed for well more than a century. It's very simple and very effective.


Correct. I'm not sure anything like this is practical, to be honest. Any of the HPA pumps you'll find will require an essentially infinite number pumps to get useful pressure.

CA99 wrote:It seems that lower pressure air requires too much volume to be useful


I think I have a solution to this too. You can actually get regulated pressure with a relatively simple design that's not too dissimilar from LPD, except that it's possibly much smaller. Essentially, you have a water/air chamber (separated by a piston, so you can fire at any angle) and a pure gas chamber. You'll have one check valve. One allows flow from the air side of the water/air chamber to the gas chamber. There's a flow path from the gas chamber to the air side of the water/air chamber through first a regulator, and then a check valve (to prevent air from flowing backwards through the regulator).

In practice, this means that you'll get a constant pressure expansion, but non-constant pressure when pumping. This means that you'll incur a certain amount of unavoidable energy loss with this approach. This might be okay; you lose a certain amount of energy due to hysteresis in latex tubing already. The lost energy is a function of the second chamber volume, mainly (the larger the volume, the less energy loss; I'll do the math to figure this out more precisely). I'll make a few drawings and post this (hopefully sometime soon or else I'll forget).

Incidentally, I vaguely recall thinking about this before I thought of LPD, but I rejected the idea because I was confused about whether it'd actually work. I'm much more certain now.

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Re: Concept: Air Wiz A10

Postby HBWW » Sat Apr 12, 2014 9:31 am

The reason I said that is because as far as I'm aware, last time it was used was in the SuperCAP, which had a huge air source tank that was hooked to the regulator. I suppose the piston chamber of this could've been carried instead of integrated with the backpack (which seems to be the design you're suggesting), but the air source chamber is still huge. HPA tanks need a lot less volume since they're operating at thousands, not hundreds, of PSI. Less volume = less space and weight. The equipment is more expensive, of course, but the ergonomic improvements are arguably very necessary to be battle practical.

Unfortunately, I don't know how to make these calculations. Essentially, you want to be able to figure out how much HPA you need, and how much of a water tank you can run at that pressure. One of the problems with the SuperCAP is the apparently cumbersome refilling process, and I think the best solution to that (short of the complex systems that both of us suggested) is sheer volume in favor of a simple design. A piston chamber doesn't allow you to store much water, and I think one that does would require too much pressure to operate practically, due to the increased surface area from a larger diameter chamber.

The LPD and other designs are a separate matter IMO, since they are built to work without HPA or some other regulated pressure source. I have a few experiments in progress with the LPD, including a new piston design that I'm hopeful will seal better (using O-rings and PVC fitings instead of the piston cups and nut/bolt assembly, although this design is generally limited to 2" sch 40 pipe for the parts I can find) and including additional threaded components (the piston chamber pipe itself has female adapters at the end) so that the piston can be removed for maintenance. I'm also looking to add a different sort of pump for it. The LPD is large and heavy, and is better suited as a mid/high powered cannon than as a primary IMO. However, it's not difficult to make the piston chamber detatchable and able to function on its own, but this is not something you can do quickly on the field without some crazy quick-disconnect component wizardry. I'll most likely end up with 2 separate homemades: A standalone air/water chamber (which is basically a 2" version of the SuperCannon II) and the LPD itself. The great part is that there are options for the pump: I can use a smaller, onboard pump, or I have a ground pump (similar to a full size bike pump, but for water) that can be used for faster, high pressure charging. Eventually, I may try to get a 3/4" or 1" pump built, which should be able to build up some fairly high water pressure against a decently pre-pumped LPD. This eliminates the air waste factor during and even between games, since you can just let a base amount of air sit in the unit for most of the day. (Not that there's really anything new here; the original LPD design had the same principle.)

I may discuss more on the LPD in the other thread I started, but I'm opting to keep some information under wraps until this is successfully deployed in the field of a community war.

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Re: Concept: Air Wiz A10

Postby CDMT » Thu Jan 22, 2015 11:35 pm

Why couldn't we borrow this double acting piston trigger setup from Karthick Robo of India to quickly open and close the front trigger ball valve while maintaining laminar flow? The only downside I see is cost.

https://www.youtube.com/watch?v=xsIAnSpWWzw

I also have another idea about the replacing the rear chamber with another setup but I would prefer to test out my idea first to confirm it's feasibility. In other words I have another crazy scheme that may or may not work.

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Re: Concept: Air Wiz A10

Postby SSCBen » Sun Jan 03, 2016 11:12 am

I've been thinking about designs along the lines of those described by HBWW and myself above, and I came to the conclusion that the design I described wouldn't work. So you need to change the design. Using a standard valve to actuate air cylinders seems to be the easiest option, but that would waste a ton of air, which would make it impractical. There doesn't seem to be an obvious way to avoid wasting massive amounts of air as I attempted above. I come to this conclusion after trying several different approaches (some of which I decided not to share) and doing the math to optimize them.

I did, however, come up with some other ideas which might prove useful in these sorts of designs or related ones. In particular, I'm thinking about how to do LPD/pre-charging better.


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