Help with APH

Build a homemade water gun or water balloon launcher and tell us about it.
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bobes89
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Joined: Wed May 13, 2009 9:08 pm

Post by bobes89 » Wed May 13, 2009 9:14 pm

Hey! Glad I found this site. Our school is starting a Water Wars tournament and I'm going to need something better than whatever anyone else has.

I've got the water gun assembled except for the pump, which I'm doing right now. I have a question about the tubing. what size tubing do I need to go on the barb so I can pump from the reservoir to the gun? And do I need to glue it onto the barb? How is the whole thing connected? I couldn't understand how to connect the reservoir to the gun.

I'm also going to try to put an onboard reservoir on the thing, but I'll save that for last.

Ok, I'm trying to assemble the pump with the wooden dowel and the O-rings. How am I supposed to fit a 5/8" O ring on the dowel into the 1/2" pipe? It almost seems impossible. I cut the valley so the O-ring fits somewhat snug on the dowel, without putting it in water yet. Do I need to cut the valley a little more, or should I leave it the way it is?
Last edited by Silence on Wed May 13, 2009 10:36 pm, edited 1 time in total.
Reason: merged double posts

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Silence
Posts: 3825
Joined: Sun Apr 09, 2006 9:01 pm

Re: Help with APH

Post by Silence » Wed May 13, 2009 10:48 pm

Hi bobes, looks like you have some good questions.

When you buy hose barbs, you pick both the pipe size and the hose size. You'll probably be using 1/2" for the pipe, and 3/8" for the hose. Note that hose measurements are for the inner diameter (ID) and hose barb measurements are for the outer diameter (OD), so you don't need to worry about fit.

The hose doesn't really hold any pressure, so you may not need to secure it with anything else if it's already got a tight fit. But we recommend buying a couple "hose clamps" just in case.

(Here's our backpack reservoir article for reference.)

For PVC, all 1/2" pipe has a set OD, regardless of thickness (which is what DWV, Schedule 40, and Schedule 80 determine). All 1/2" fitting have a set ID. What's weird is that the set sizes are much larger than labeled, at least for pipe under 3" in diameter. 1/2" schedule 40 actually has an ID of about 5/8" and an OD between 3/4" and 7/8".

The 5/8" O-ring might need a 3/8" dowel...I'm not sure. But you're doing the right thing by cutting a groove. Make sure you lubricate the piston with silicone lube to make sure you're not trying to cut too deep a groove. Once lubricated, shave just a bit more out of the groove if you need to make the piston slide easily. Also, make sure the groove is a consistent depth all the way around...it might be too tight at one spot, which could make you carve too much somewhere else and lose the seal.

Good luck! :)

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C-A_99
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Joined: Tue Aug 01, 2006 11:09 pm

Re: Help with APH

Post by C-A_99 » Thu May 14, 2009 2:43 am

The pump will most definately be the most problematic here. I have yet to get a pump to work reliably. (and fo the ones that do work, their seals break off) This is made worse by the slightly inconsistent ID of the pipe.

You shouldn't need the clamps (though its still not a bad idea to get them); the tube should slide snuggly onto the barb and seal. 3/8" ID is a good diameter for this; you don't need too much.

bobes89
Posts: 2
Joined: Wed May 13, 2009 9:08 pm

Re: Help with APH

Post by bobes89 » Sat May 16, 2009 2:27 am

Thanks Silence and C-A_99. I got the pump to work effectively, all I needed was one O-ring. I just need to put vaseline on the O-ring to make it pump smoothly.

I figured out a better way for the stopper to be used on the pump. Instead of putting a washer in the T joint, I hammered a nail through the pre-drilled hole at one end of the PVC, and then hammered it into the other end of the PVC, so the cross-section looks like a circle with a nail through it. It works very well, and you don't have to worry about the washer falling out.

But yeah, the thing works, I just have to pressurize it more. How many pumps do you think it should take to pressurize the gun?

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Silence
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Joined: Sun Apr 09, 2006 9:01 pm

Re: Help with APH

Post by Silence » Sun May 17, 2009 1:17 am

Vaseline may not be the best lubricant. If the O-ring is made of natural rubber (hard to tell), oil-based lubricants will wear it down over time. Traces of oil could also affect the seals in the ball valve if those are made with natural rubber. Silicone lubricant is the best choice.

I'd have used some epoxy on the nail, just in case, but if this works, then no worries. It's a simpler solution, too.

The number of pumps you'll need to pressurize the soaker depends on the volume of the pressure chambers and of the pump itself.

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