Developing an APH

[HBWW]

After using a SS 300 at MOAB (league season opener), I decided I simply had to have one, but without the price premium. (I'd rather the money go to durable stuff that won't break as easily.) So I finally decided I had to build a APH.

At the same time, I was having major issues with my CPH with bladders constantly breaking. Either I overpump the LRT, or it simply doesn't last that long (maybe its the former, which causes the latter), so I experimented with balloons for a chamber. The result was much, much more powerful due to significantly improved flow, but I did it completely wrong; there was no stem for the balloons; I literally just stacked them from nothing. (i.e. Imagine a k-mod that starts on one balloon instead of an actual bladder.) Because of this, balloons were ripping off, the seal/clamp was going bad, etc. so I gave up and had one last resort that I know would last a long time: the APH chamber.

Original CPH from when I built it in 2007:

CPH.jpg (99.22 KiB) Viewed 4771 times

I got the parts and built the PC earlier this week, then attached it.

CPHtoAPH.jpg (144.59 KiB) Viewed 4771 times

After some testing today, I was expecting XP-like pumping and performance. After all, isn't the classic APH design almost as timely as the classic SS 300 itself?

Nope, not quite. I could not pre-pump the PC to any useful amount. I even had to let out extra pressure on one test in order for the pump to be able to keep drawing. I'm quite sure the problem isn't even the pump seal itself, as this thing has worked solidly over the last year from intensive testing and has not had an issue. Once the water came in, I even managed to pump it up until my arm could no longer do it, and I never got a single pump squirt or leak indicative of a bad seal.

I conjecture that the problem is somewhere else: the enormous dead space from the pump and 2nd check valve. This was never a huge problem when the homemade was a CPH because water doesn't compress, but air is a different story.

I'm 90% sure that the whole problem goes like this:
- Inside the pump, the pressure created has to reach the amount of pressure present in the PC. This is the resistance you feel in the pump.
- Due to the dead space between the pump and the 2nd check valve, and the fact that air compresses, the pump cannot reach any useful pressure level with air because of the excess air volume. (That would otherwise be air pressure if it wasn't there.)
- Without enough pressure, the pump cannot add more pressure to the air chamber.

Why do we almost never hear of pump lagging or bouncing in most stock water blasters? Because the space between the check valves and pump is kept as tight as possible. Drenchenator's DR-4 does this part 100% right. http://forums.sscentral.org/showthread.php?t=5723 (See 4th picture.)

Now, am I just reciting common knowledge at this point? Because judging by the homemade designs we put in our guides (on SSCentral in particular) and them purport to be effective homemades, this is not something that appears to be well known at all, yet is a major usability and practicality issue. It may not apply as much for CPH's, because most of the time you're pumping water (non-compressible as we know) instead of air, so once the internals are filled, there's no risk of bouncing/bumping unless air finds a way back in. (When testing with a stock FF pump [which presumably has a perfect seal], I ran into this problem very often, especially if the pump comes out while pumping and air gets in, creating an annoying air pocket between the pump seal and the water.) The whole point of homemades is to combine the efficiency and effectiveness of stock blasters with the power and durability of DIY solutions.

With all that said, I haven't quite developed a plan for moving forward. I could design the APH so that both check valves are arranged similarly to that on the SS 300, but unless I use special valves from McMaster, that will take up a lot of space.

In addition, I haven't decided between using 2-3 3" chambers, or 4 2" chambers. XP's are typically somewhere between the two, but I feel that having more 2" chambers would balance better, so I will most likely go for that. However, this is nowhere nearly as important as the pump problem that I currently need to address. (And plus I have to convert the thing back to a CPH, although I might experiment with a stock pump [seal known to be perfect] before then.)

I considered that using lower diameter internals could be very beneficial in reducing dead space, but could also reduce flow. 1/4" seems rather small, considering most CPS tubes seem to use closer to 3/8", and low diameter tubing seems to be part of why the Flash Flood requires more force to pump than other blasters. Then again, I could be wrong and that tube ID from the 2nd check valve to the pressure chamber does not really matter as long as it isn't ridiculously constrictive. (i.e. 1/8" or something extreme.) I guess the fluid dynamics wizards here can help me out with deciding that. Perhaps all that really matters is that the check valves are all close to keep the pump from having issues.

So with that said, I might as well do a paper sketch.

APHconcept.jpg (67.37 KiB) Viewed 4771 times

It's basically the SS 300, except in PVC with fat, overpriced check valves. I should seriously consider the McMaster ones if I can't shrink this down. (I'm already trying to by using threaded elbows and check valves, which keeps it modular for road/flight trips too.)

Now... Discussion time!

[the oncoming storm]

Have you seen Typooninator on YouTube?, seems like a good starting point for a homemade 300.

[HBWW]

Can't find anything on Youtube for that. Do you have a link?

[the oncoming storm]

http://m.youtube.com/watch?v=aicfg2qoCv ... re=related

This took me a good 5 minutes to find, and I knew how to find it. Very obscure

[HBWW]

If you spelled it correctly, I would've found it instantly.

Not sure if I like that design, I think I may have to take a different approach than making the whole thing out of PVC. (i.e. Using smaller check valves/vinyl tubes, stuff Drenchenator used on the DR-4.) And lol, that pump leaks insanely.

[the oncoming storm]

Why not base it off of the DR-5 that he is working on?

And I know I spell poorly, but is is getting better 2 years ago that post would have been almost unintelligible.

[HBWW]

I don't quite have the materials, time, and skill for a DR-style design. I actually want to avoid the whole deal with triggers entirely and stick to a good old ball valve arm.

[Drenchenator]

Some parts of the design of Cloudburst (DR-5) are very much geared towards CPS, so as a whole I don't think it would work well as an air pressure gun.

I'd recommend 3" chambers over 2" chambers purely because they hold much more water. They are kinda bulky, though.

You should probably put the 2nd check valve inline with the barrel and the ball valve, though this just might be opinion. I never like the stacked check valve arrangement that some people use because it makes the gun the too tall. Ben kinda did the same thing by adding a lot of dead space after the pump tee in the APH. I always thought the design should be tighter, and would work better if that dead space was reduced or removed. Essentially, the pump tube should be as close to the barrel and ball valve in height as possible. This might make the gun unbalanced, though, so take it with a grain of salt.

[HBWW]

I may end up using mostly or all threaded connections; I could use an all-way-threaded tee, followed by an elbow that connects to the 2nd check valve (Or to a nipple first if I can't find an elbow male on both ends that's PVC.) This would minimize dead space, not as much as having it directly after but would still help. Only way to really reduce dead space after that is to use tubing of lower ID and special small check valves.

[Andrew]

As already mentioned, the deadspace is the issue. It's something I thought about a little bit, but pretty much ignored when building my homemade (It doesn't need to pump air to pre-charge) You could reduce the deadspace in the design you've already made (there is quite a bit of exposed pipe between the tee and the check valves). You probably know this (based on the paper drawing design), but you'd need to reduce the exposed length of pipe between the intake check valve and the pump aswell. If you took the current design, and shortened the exposed pipes until the fittings were practically touching each other, you'd reduce the deadspace volume by between 1/4 to 1/3 of the pump's volume (guesstimated by approximately measuring the total length of exposed pipe compared to the pump length).

Not sure how you'd shorten those exposed lengths if they've been solvent welded, and if you're going to have to build a new one anyway because of this, the paper design would, of course, have less dead space as it has one less elbow between the two check valves.

[soakinader]

I wish I could be motivated to build some homemades. Order lots of valves, joints, and LRT off of McMaster, and go crazy. Maybe even find a cool shell to put it inside.
Does anyone have a list/guide to the Mcmaster website for water gun parts?

[HBWW]

I plan to be using this APH project as a chance to write up a guide for it, which I haven't done before.

For something as expensive as a check valve, I'll never be buying them solvent-welded again. I'm hoping to require as little welding as possible in the entire project, if at all, but I will also avoid metal parts since they add unnecessary cost and weight, and can strip PVC threads if you're not careful.

Edit: Once the new pump design is completed, I'll likely dig right in to this after completely deciding the design. Of course, I have other blasters to fix in the meantime. (Note to self: Parts list are in the HBWW Dropbox folder!)

[HBWW]

Here's a sneak preview at the new design.

What's missing from the photo:
- SuperPiston MK II Pump (http://www.waterwar.net/site_wwn/board/topic6076.html): Already built and tested, and works fairly well so far.

- Bracing between pump and PC area: I decided to use a pipe outlet/snap-on tee this time. Typically, you're supposed to primer/cement them onto the pipe, then drill a hole through and that gives you a tee connection anywhere along the pipe. However, no one's forcing me to drill, so they could make good pump supports. In the photo, you only see one pipe bracing which was available at Lowe's. However, I have to order the pipe bracing for 1/2" pipe at McMaster Carr (which I stupidly forgot to do earlier.)

- Backpack connection. The check valves (from McMaster Carr) are nice and compact, but also have a design quirk that prevents me from putting the barb fitting on directly. I need a threaded extender to do this, or I need to switch to a 1/2" barb. (The latter of which I don't have enough parts for anyway for the rest of the backpack.)

- Screen between the pump shaft pipe and 1/2" male adapter: This screen stops the pump from going in too far and potentially getting stuck. I will stop the pump via handle/cap first, once the handle is assembled. (Which I may do properly this time instead of using a lot of duct tape.) Unfortunately, this screen also prevented me from being able to remove a ton of primer/cement gunk that resulted from excessive use. (Or perhaps from using cement too soon after primer? I read somewhere that you're supposed to do that though.)

I have two backpacks ready: One for this and one for the CPH. The rest of the APH functions quite well. My conjecture about the pump dead space turns out to have been correct, as I managed to get a lot more air pumped into this than on the CPH with the same PC. However, I can tell that there's still a lot of dead space left that's preventing the pump from reaching its full potential. The decision to use threaded check valves may or may not have contributed to this.

Anyway, I'm looking forward to finishing this up. Just need those last few parts: 1/2" threaded extender, 1/2" male adapter, and 1/2" snap tee/outlet. I could hack together some quick solutions and be more wasteful for parts that have better uses, but I'd rather not do that.

[the oncoming storm]

Sounds good what kind of ranges is it getting ?

[DX]

Anyway, I'm looking forward to finishing this up. Just need those last few parts

My guess is 0 ft.

[HBWW]

I got a burst of air to shoot 10ft or so? How do you even measure those? Anyway, haven't dunked it in water to test yet, may do that later today or tomorrow. (Just needed a part to hook it to the backpack.) Will have to setup for a proper range test sometime, I guess, but I almost never do those lol.

Edit: Just did some testing. Forgot to get pictures though.

Performance was neither impressive nor disappointing. Shot time is the main problem since there's only one pressure chamber. The pump is also leaky; I will have to investigate later.

I may have to put this project on hold again; got a few things coming up. In fact, I may opt to hold off on the guide/details until later anyway.