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why are bike pumps so s#1+ ?

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why are bike pumps so s#1+ ?

Unread postAuthor: lemming124 » Sat Nov 20, 2010 7:28 pm

I've been looking at a number of homemade pumps on this forum http://www.spudfiles.com/forums/easy-st ... 13277.html
http://www.spudfiles.com/forums/my-firs ... 20370.html
from what I've gathered the standard formula is shaft + piston + check valve. My question is what exactly is the inhibiting factor on standard bike pumps (like this: http://cn1.kaboodle.com/hi/img/b/0/0/54 ... 5178054000) The only answers I can think are the difference in the size and/or shape of the pump shaft and/or the construction/function of the piston. Could a standard bike pump be modified to produce higher pressures?

thanks.
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Unread postAuthor: saefroch » Sat Nov 20, 2010 7:49 pm

You are correct, pumps are oddly simple.

Why can't you produce high pressures with a bike pump? If you've ever tried, it becomes obvious. Pressure = force/area, or Force = pressure * area. So if you increase the area of the bottom of the pump head (or piston) there is a greater force against you when you're pumping created by the pressure you're building on the "in" side of the check valve.

To reach higher pressures you generally need a smaller diameter pump head (or piston), unless you can just keep cranking up the amount of force you place on the pump handle. The amount of force you can apply to a manual floor pump like a stirrup or a bike pump is limited by your weight. To produce a greater pressure with the same amount of force, you need a smaller area.

There's also this pump, but I didn't include a how-to.
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Unread postAuthor: lemming124 » Sat Nov 20, 2010 8:11 pm

thanks Saefroch, that explains it well
I feel like quite the idiot -_____-
time to start building a stirrup pump :)
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Unread postAuthor: Lockednloaded » Sat Nov 20, 2010 8:13 pm

I don't know your location, but if you have walmarts in your area, I found a solidly constructed, reliable 200 psi pump (I've pushed it to 260) for only 20$, when I get home I'll check the brand for you
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Unread postAuthor: saefroch » Sat Nov 20, 2010 8:20 pm

What pressures are you trying to reach? You may just be able to buy a pretty good pump for those pressures at a fair price.
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Unread postAuthor: lemming124 » Sat Nov 20, 2010 8:33 pm

haha I wish we had Walmarts down here (that should be a good enough clue about my location ;) )
Commercial high pressure pumps have been in my consideration for awhile.
I guess I'd be aiming for around 200ish. I've taken a blowgun with a schrader to around 160 with my bike pump but that was a real pain and took far too much effort considering that the chamber volume was less than a cubic inch :/
thanks for your help.
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Unread postAuthor: Insomniac » Sat Nov 20, 2010 9:41 pm

If you're making your own pump, be very careful to get a high quality check valve. If it fails, the pump is suddenly going to turn into a pneumatic ram with quite a lot of force behind it... It seems obvious, but you need to be aware of the risk.
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