APH vs. CPH: highest pressures?

Build a homemade water gun or water balloon launcher and tell us about it.
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APH vs. CPH: highest pressures?

Post by Jasp » Sat Jul 22, 2006 1:29 pm

I've had thoughts about making my own powerful water gun for a couple of years, but only just recently stumbled apon SSCentral, and learnt about how I'd go about doing that. (Thanks to everyone who has contributed to it's content BTW). I'm going to start gathering materials for my own homemade pretty soon. But now, after reading Ben's CPH thread, I'm not sure weather to stay with my current (APH based) design or not.

What I want to build will hopefully be a good sharpshooter gun. My current design is pretty much just a standard APH, except for one main difference. It will have a bottle of highly pressurized air hooked up to a ball valve connected to the PC. Additional air can then be fed into the PC when required, making the air pressure higher, increasing power, which will hopefully allow for increased range. It'd would otherwise allow for standard use, increasing pressure with a pump.

But now I'm considering building a CPH system instead. The choice I make will all come down to which one it is that can be pushed to the highest pressure, regardless of the need of an additional source of pressure or not. I've also thought about making the PC removable/swappable, using a "screw connector" (better/correct term?) on the pipe, which would allow me to experiment with both types. Any advice?

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Post by SSCBen » Sat Jul 22, 2006 1:50 pm

Welcome to Super Soaker Central!

For a hand pump alone, the constant pressure design will be better. The advantages of having a constant range and output are very substantial. You can get comparable range and output on regular nozzles, however, you will not be able to get the level of a riot-blast the air pressure designs can offer due to the flow restrictions of the tubing barb used (unless you use a larger tubing barb). With a really thick chamber too, you'll be everyone else in distance. I like the rubber-based CPS design for it's simplicity.

You have to remember however that the rubber-based CPS designs and the air pressure based designs operate on completely different principles. While pressure will exist in the rubber-based CPS system, the system operates on the elasticity of the rubber. For a while, Larami reported pressures on their water guns, and the basic XP water gun was at 40 PSI, while the CPS 2000 was only at something like 22 PSI! The system simply does not use pressure to operate. If pressure existed in the rubber system, it would expand the rubber further to create more volume. The rubber however, of course will make a bit of pressure to keep the forces between the rubber and the fluid equal.

However, if you are using an air injection system of some sort (joannaardway made something similar), you might as well slap a regulator on and turn it into a CAP design - a constant air pressure design. Only two water guns have been made with this design, but it works wonderfully and you have no limit on pressure and flow. That's what I would suggest if you intend on using an air injection system of some sort and want it to also be CPS.

Injecting air into the CPS system would probably just cause the massive volume of air needed for high pressures to expand too far and burst the bladder. It wouldn't increase performance, rather, it would take away your capacity.

Some people over the years have thought of ideas about pressurizing around the CPS chamber that I suppose might work with the air injection system (or should this be called the "post-charger" system?). I know someone will come on and suggest this if I don't mention it. I don't like the idea. It puts stress on the CPS chamber and simply would be hard if not impossible to implement.

As you can see, there are loads of options. Personally, I'd go for a super-thick chambered CPS water gun because it's simple and wouldn't require you to inject more air to get higher performance than a hand pump would allow. I also am somewhat biased - I want to see more CPS designs. :)

Stay around for someone else's insight. I'm sure someone will cover something I've missed.

ben@sscentral.org / Please read this before emailing or PMing me

Do not ask me water gun questions by email or PM. Please post the question at the forum. Private questions and suggestions are welcome by PM and email. Also, I do not sell or buy water guns online.

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Post by Silence » Sun Jul 23, 2006 10:27 pm

Welcome to SSCentral, Jasp! It's actually pretty hard to cover anything that Ben might have missed after his long reply... ;)

Anyway, it sounds like an air-injection system with canned air as the source would be far too...um, complex...for your purposes. However, you can always consider a semi-PCgH (although perhaps not of joannaardway's copper style) as a much simpler method to add extra pressure if you have the time to pump it.

Do not plug in a high-pressure air container unless you're using a regulator. PVC is definitely not strong enough to take more than 100-200 PSI even if you get the correct full-core/pressure-rated Schedule 40 type. This means you'll either have to use expensive, heavy, and less usable metal or that you'll have to use a regulator--which adds the complexity I mentioned earlier. I'm not too sure how strong the copper joannaardway used is or whether it is too heavy or not for your purposes, but I'm just saying this as a warning...

If you're looking for a larger variety of ways to get greater pressure with less complexity and less pressure (and thus less potential for danger), you could also consider a multi-stage pump. Granted, it hasn't been done before and will certainly add more complexity and weight, but it provides greater functionality in a more practical package. It simply makes more sense to build a complete CAP soaker as Ben suggested if you're using canned air.

Go with the CPH if it's a project you're willing to take on--imagine the power of an APH (or close to it, at least) with the advantages of CPS. I can see why Ben advocates them, and I might build one if my APH works out well. As he said, the bore will be very small--but with a 3/8" or 1/4" riot blast, you can't really argue that it is weak. Actually, if I were to build one, I would use a third layer of LRT on the inside and downsize to 1/4" pipe--and if you're trying to build a "sharpshooter" weapon, there's nothing wrong with that approach.

And while we're at it, could you explain the APH design you had in mind? I'd be happy to make a few suggestions if they're needed, and I'm sure that goes with the others here.