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HPA pump help.

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Unread postAuthor: warhead052 » Mon Jan 30, 2012 8:52 pm

Nah, I don't want to get a fridgy. I want to be able to use this more or less on the go. One of the reasons is the same as yours for your hammer valve rifle.
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Unread postAuthor: Fnord » Mon Jan 30, 2012 8:59 pm

A lever handled pump would be better if you're feeling ambitious. A linear stroke has a terrible mechanical advantage since the force required doubles every time you push in half the remaining length. With a normal lever, the mechanical advantage approaches infinity as the pump reaches 'top dead center', so the force for the last third of the stroke feels fairly uniform.

The problem is you'll be cutting your stroke length in half to allow for the lever mechanism, but it balances out since you'll be able to comfortably use a 3/4" tube instead of a 1/2" one.

Start out with your original design since it's simple, but make it easily removable in case you want to upgrade later.

Also I'd recommend something thicker than 1/4" for the pump rod. A bolt-and-washer design will work well for the pump head.
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Unread postAuthor: warhead052 » Mon Jan 30, 2012 9:16 pm

Ok. I will do 3/8" then, and a bolt washer piston. Thank's for the help guys. Expect a new rifle within the next few months.
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Unread postAuthor: MrCrowley » Mon Jan 30, 2012 10:18 pm

warhead052 wrote:the check valve would be homemade, with a ball bearing and a spring, as well as a rubber seal for the ball bearing to push against.
I'd spend the most money on the (commercial) check valve. Just talk to BriantheBrain about failing check valves.
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Unread postAuthor: Hawkeye » Mon Jan 30, 2012 11:16 pm

Actually a homemade check valve with minimal inlet would be a better choice than a commercial one.
The input from a handpump is pretty minimal so it only needs enough room for the air to "hiss" past the seal. Even if it locked open or failed completely it shouldn't allow enough air back out to form a ram with the pump handle.
I just used a solid aluminum rod for my half inch pump.
Definitely a good handpump is a big advantage over a fridgy unless you w nt to be yoked to an electirical source.
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Unread postAuthor: MrCrowley » Mon Jan 30, 2012 11:22 pm

To be fair, Brian's check valve was commerical (although not rated for the pressure he used it at) and failed at 65bar, not 30. 400-odd PSI probably wouldn't be that bad if the check valve failed and if it means you can minimize dead volume, go with that option if you want.
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Unread postAuthor: Petitlu » Tue Jan 31, 2012 2:06 am

Here are the pretty PAC to a French friend like me! :D
QDV and has a built-in pump


http://patator.frbb.net/t8423-2010-paca-mkii
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Unread postAuthor: warhead052 » Tue Jan 31, 2012 9:27 am

Petitlu, that's sort of what I am aiming to make.

Crowley, Hawkeye, you two both have valid points, but hawk you have hit the spot. I don't want to be stuck hooked to a fridge compressor.
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