Homemade design advice.

[frankenbike]

Originally posted by Doom@Jun 23 2005, 01:09 PM
As you said at iSoaker.com, you could add a divider to separate the air and the water in the CAP system, but the problem is pushing the divider back up. MrPukeOnYourHead used a dowel rod many years ago in a design like that, but that's not practical at all in a backpack!

Well, if you have a system that is filled by a water hose, you can use a quick fill type system to push the pistons back up. Unfortunately for my purposes, no garden hose would be available, so it's moot for me.

You could make a system to use pressure to move the divider back, but that would waste air and likely make the water gun more complex in use.

You could automate it so it happens automatically when the pistons reach their full stroke, but that would make the design vastly more complex. Like machine gun complex.

A manual system would obviously be easier than using a dowel or pumping though. Just flip a valve on and off, then pull the trigger/open the valve that lets the water exit the gun to vent excess pressure. Oh yeah, you'd have to have a second valve you open to vent pressure on the "pressure side" of the piston. I think you need that anyway to disarm the water gun, since there'll be latent pressure in the system even when you turn the CO2/CAP valve off.

I'm personally mostly interested in constant pressure - a logarithmic drop would be an improvement over the linear dropping of regular air pressure, but not much in my book. I still have my doubts on whether or not a piece of rubber tubing could handle outside pressure very well.

Well, I'm a subscriber to the CAP design style. That's what the system I'm designing is, though I use CO2 for volumetric efficiency in my design. But as the pressure drops below your set CAP pressure and you run out of pressure, you still have the same problem.

As for the rubber handling it...the pressure should be equal on both sides of the rubber. It's only the differential of the pressure with the outside air that allows the water to exit the gun in the first place. Your main problem with the latex material is the limits to its elasticity. The air pressure you can hope to achieve, short of maybe 5000psi or more, is insufficient to break the molecular bonds of the latex as long as you have the same pressure on both sides of it.

As the water leaves the its own pressure chamber for the nozzle, the decrease in air pressure is comparatively gentle, and shouldn't impact the elasticity of the rubber.

In other news, I've found that you can order fire hose nozzles from McMaster.com! Nozzle D (brass) with a 1" diameter and a 5/16" orifice would be an excellent, but expensive choice when looking for maximum performance. Because it is made of brass, you should not have trouble drilling a nozzle of a larger size in. If you are dissatisfied with your pressure washer nozzle, please give that nozzle a try!

The main limitation of the pressure washer system is the output side of the gun in the one I ordered is supposedly 3/8". Most are 1/4", and this one appears to be unique, unless they are falsely advertising it and it too is 1/4".

In any case, I have a lathe and can pretty much make any kind of nozzle I want. I think I have some appropriate size aluminum and nylon in the garage (nylon would be better because it's corrosion resistant). Brass is harder to tool, though I might have some of that as well.

You've sparked some interest in my homemade water gun creation and instead of using my saved money to replace my stole MP3 player, I'm planning a CAP design to address a few problems I have with my current homemades.

I'd get the MP3 player. Much more versatile. Then save up again for the CAP.

We seem to be the only ones participating. But if you have access to the site records you can see how many are reading.

Maybe others are waiting until I actually get around to building the gun and seeing the results. I'll probably set out to some building supply places to start getting an idea of what's available and work on my parts list later today or tomorrow.

[Spinner]

Originally posted by frankenbike@Jun 23 2005, 09:47 PM

I'd get the MP3 player. Much more versatile.
[right][snapback]25479[/snapback][/right]

Well, you can't shoot water with a MP3 player...or can you? An iPod case mod, perhaps? :lol:

[Ben]

I would get the MP3 player, but I'm just going to wait for the prices to drop and space/features to be added. The one that I previously had was excellent, but if I needed to listen to some music in the past few months, I found other ways.

I also enjoy making water guns far too much to pick an MP3 player over one. To me, this water gun would be worth several MP3 players.

[frankenbike]

Well, it looks like I'm going to have to give up on the 6" pipe. Too uncommon in these parts and too expensive. 3 13-inch long 4" pipes should give me a little over two gallons, and it's way cheaper. More complicated design, but that's the price I have to pay. Easier to fit in a backpack though, and more svelte.

I can get a 10-foot 4" sch40 pipe for around $15 or so locally. 5 feet of 6-inch pipe from McMaster would cost about $30 plus tax. And I can't just root through the bins and see what I need to build it. I'd have to order everything.

One place does have 6" sch40 pipe around here, but they'll only sell it in 20-foot lengths, at a cost of $96. Fahgettaboutit. Might give shopping one more shot in the more industrial area of LA next week.

Oh yea, I did find a nice online volume calculator if anyone needs it for their own designs:

http://www.csgnetwork.com/volumecalc.html

Enter the radius and length in inches, and it gives you cubic inches. Then you go here:

http://www.onlineconversion.com/volume.htm

...to for an online converter to convert cubic inches to gallons or liters or whatever.

[Ben]

^ Possibly I could add a few calculators to our own site? Those do save time and probably would help a lot of people out in homemade water gun design.

6" pipe apparently is available where I live in a pumbling supply store called Noland's. I had to ask a local spud gunner where he bought his 4" pressure rated pipe.

[frankenbike]

Originally posted by Doom@Jun 25 2005, 10:10 AM
^ Possibly I could add a few calculators to our own site? Those do save time and probably would help a lot of people out in homemade water gun design.

6" pipe apparently is available where I live in a pumbling supply store called Noland's. I had to ask a local spud gunner where he bought his 4" pressure rated pipe.

I haven't found a local supplier of sch80. Yet. But even Home Despot has sch40. Which should be adequate. I might butress the 40 with retention straps to increase the effective pressure rating. I haven't decided whether to use worm gear clamps or just put PVC sleeves on the tubes. I'll just have to eye the bins and see how I can use things for purposes they weren't intended for.

6" is something that is used for big time irrigation systems. If you live near a rural area, you're more likely to find it handily. Since I'm in the Los Angeles area, there isn't much in the way of "rural" close by. So I'll do some cursory searching locally next week, because maybe an "industrial" supply place might have it on hand for manufacturing. But I won't hold my breath. Two gallons is still 16 pounds of water, plus all the other hardware and the weight of a backpack itself. I'm guessing even with that smaller capacity than the 3 gallons you get with two 12" 6"-diameter pipes. Since I don't need an air gap with the CO2 system, I don't need the volume.

Volume calculators would be a good idea. If you can find a liter/pressure per liter/water calculator, that would be handy as well.

[frankenbike]

Well, the Campbell Hausfeld pressure washer gun doesn't really match the advertised description. It's internal diameter is 1/4" just like all the others, even though it states 3/8" all over the specs.

Back to the garden hose gun, I guess. Too bad, because it looks pretty cool and dangerous, and the trigger has a really nice feel

Edit: Oh yeah, you told me so, but did I listen? [John Belushi Mode]NOOOOoooooooo[/John Belushi Mode].

[Ben]

That's interesting actually. I'd return it because it wasn't as it was reported.

I went to Noland's to see if they had any 6" pressure rated pipe... I actually entered through the employees entrance because it wasn't labled. I felt confident that they would have 6" pressure rated pipe, but they said they were out and will have some by next week.

[frankenbike]

Originally posted by Doom@Jun 29 2005, 05:38 PM
That's interesting actually.* I'd return it because it wasn't as it was reported.

Already got my RMA and they pay the return shipping. Costs me the initial S&H though. C'est la vie. It was worth a try. It's pretty dang cool looking.

When I talked to the woman at C-H, I explained what I was using it for. She said, "So, you're an inventor?"

I replied, "Uh, more like a mad scientist than inventor."

I went to Noland's to see if they had any 6" pressure rated pipe... I actually entered through the employees entrance because it wasn't labled.* I felt confident that they would have 6" pressure rated pipe, but they said they were out and will have some by next week.

Well, I've been window shopping pipe parts to figure out how to actually flesh out my design. The closest Lowe's is 8 miles through very ugly LA traffic in a bad neighborhood, next is about 12 miles through ugly traffic in a better neighborhood. In any case, I'm looking for tank pressure fittings for the tank outlets, and if I don't find them, I'll have to make some with PVC external NPT size adaptors and the lathe. We'll see what Lowe's has.

Also, the 4" SCH40 pipe I found is black ABS. Supposedly more durable than PVC and it's black. Bonus. Don't know what the rules of bonding ABS to PVC are though. The caps and plugs in 4" and 2" are all ABS, so it wouldn't be a problem there. But the reduction to 3/4" for the lower pipe to connect all the tanks is a bit more problematic. The pressure equalizers on top shouldn't be a problem, because I'm thinking of using 1/4", soldered copper pipe up there. I'm still working out a teflon tapeless 2" fill/pressure cap using a pipe plug and gasket design, and a pressure release valve (so when I'm done soaking people or washing the motorcycles, I can relieve the pressure even if there's still water in the tank).