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Old 05-25-2010, 06:22 PM   #1
Ares
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Default Newb questions for building an APH

First post so hello everyone. I'm looking to build my first APH and had a few questions. Based off of these instructions http://www.sscentral.org/homemade/aph/construction.html can the pump be built on a larger scale to help with less pumping? Could the system also be made out of larger pipe to hold more volume or will it lose pressure? Is a 3rd or 4th PC worth adding? Thanks for the help. I'm going to build this weekend and then I'll post some pics.
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Old 05-25-2010, 08:58 PM   #2
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Default Re: Newb questions for building an APH

Quote:
Could the system also be made out of larger pipe to hold more volume or will it lose pressure?
A larger pump diameter will require less pumps, but it will also require a tighter seal and will be harder to push in. It's usually best to have a small, long pump.
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Is a 3rd or 4th PC worth adding?
It depends. Do you want a heavy assault cannon, or a light running-and-gunning weapon? Build it how you prefer. Also, instead of having a lot of PCs, It might be better (and cheaper) to have one or two big soda bottles. However, you will have to be careful not to damage the bottles, and if you manage to pump it up too much, the bottle may burst.
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Old 05-25-2010, 09:14 PM   #3
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Default Re: Newb questions for building an APH

A larger diameter pump would not require a tighter seal at all. However, you will still need to operate the pump with more force since you are pushing in more water at a time. This also limits the maximum pressure you can get to more than a 1/2" pump because the APH's design allows it to be safely pressurized to higher levels than humanly possible to pump. (Unless Chuck Norris is pumping the water blaster or something.) Stick to 1/2"; it's the ideal balance between pump volume and pump difficulty and maximum achievable pressure.

Adding PC's provides the same benefit as increasing the surface area. You want to stick with two higher diameter PC's over, say, 3 or 4 lower diameter ones. Assuming you're using 3", adding more PC's will require more pumping to fill it up to full pressure, though it does give you more capacity at a time to work with.

Having less volume in the PC makes it easier to pump up. This is not true for CPH's though since the pressure is constant and you never have to pre-pump air to get good performance. I would stay away from soda bottles since this is an APH and will be pumped to higher pressure levels than stock water blasters.
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Old 05-25-2010, 10:00 PM   #4
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Default Re: Newb questions for building an APH

Are you sure it doesn't require a tighter seal? If you're pushing in more water at a time, wouldn't it put the O rings under more pressure and cause it to leak if the seal isn't tight enough?
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Old 05-26-2010, 07:26 AM   #5
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Default Re: Newb questions for building an APH

Thanks for the info. I'll stick with a 1/2" pump although I might jump up to 2 - 4" PC's to gain a little capacity. Has anyone tried a leveraged pump like on an air rifle? Have a hinged point type lever that would give more leverage to pump a larger bore pump.
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Old 05-26-2010, 01:22 PM   #6
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Default Re: Newb questions for building an APH

A seal must match just right. Too tight and it won't move and too loose and it won't seal. The only thing that makes larger seals more tight is because there is more friction from the higher surface area (I might also be wrong on that, I can't remember exactly), otherwise you need to find the same balance between good seal and too tight regardless of diameter. Lubrication is a must if you're using O-rings.
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Old 05-26-2010, 04:27 PM   #7
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Default Re: Newb questions for building an APH

Has anyone tried square cut o rings? That's what we use on hydraulic cylinders for high pressure so I wondered if they might seal better?
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Old 05-26-2010, 06:24 PM   #8
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Default Re: Newb questions for building an APH

Circle is better. It stays lubricated longer (I think) and pressure is applied the same everywhere, making it less likely to leak. (I think)
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Old 05-26-2010, 07:29 PM   #9
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Default Re: Newb questions for building an APH

Circular cut O-rings are easier to seal I believe. Square cut requires more precision which can't happen with PVC homemades.

The ideal seal is the type used in actual water gun pumps, which is like a small cup seal similar to the one in the SuperCannon II but much softer. Some of these seals have little bumps or ridges on them that slightly resemble an O-ring. Either way, these types of seals work the best by far and never leak, but I don't know how to get them.
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Old 05-26-2010, 08:08 PM   #10
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Default Re: Newb questions for building an APH

Maybe McMaster sells extra small piston cups.
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Old 05-28-2010, 11:47 PM   #11
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Default Re: Newb questions for building an APH

Yes, you would have some trouble insert square O-rings, but if they fit, they may work. Round ones have much less material at the outermost edge, so I imagine they'd deform more easily.

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Originally Posted by C-A_99
The only thing that makes larger seals more tight is because there is more friction from the higher surface area (I might also be wrong on that, I can't remember exactly)
When you squeeze a fat O-ring to fit in the pump tube, it pushes back and creates a lot of force in that direction - i.e. normal to the walls of the pump tube. And more normal force means more friction.
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Old 05-29-2010, 02:09 PM   #12
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Default Re: Newb questions for building an APH

Silence is back!
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Old 06-01-2010, 02:29 AM   #13
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Default Re: Newb questions for building an APH

Thanks for the welcome, and we'll see how long it lasts.
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Old 06-01-2010, 08:58 AM   #14
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Default Re: Newb questions for building an APH

Well I started but didn't get much done. Just cut some pipe to length. Family wanted to go do stuff for the holiday weekend so I'll work on it this week and post the progress.
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