7/11 Are there floor model bicycle pumps that can switch between high
volumn and high pressure? I can barely pump up to 85 PSI for my bike
and I'm wondering if they have a pump that can switch to pumping
high pressure, like some of those fancy portable pumps. ok thx.
\_ How would such a thing work? PV=nRT, with n,R,T relatively
constant. Since the compression cylinder would have to be
a constant volume initially, it seems like it's always going
to be a PITA to pump to high pressure, no matter what?
\_ Decent floor pumps don't have difficulty pumping to high pressure.
-tom
\_ I just returned my $25 made in China pump for a $30 made in
Germany pump. Both of them are hard to pump after 95PSI which
was a big disappointment. It took a lot of efforts to get up
to 115PSI. After 95PSI, if the pump handlebar isn't pressed
down completely, the pump handle forces it to pop back up
probably because the valve is opened up and the pressure built
from the tire pumps the handlebar upwards! Is this normal? -op
-tom
\_ No, it's not normal. I have something similar to
http://www.performancebike.com/shop/profile.cfm?SKU=21099&subcategory_ID=4360
and I can easily pump to 120psi. One thing: Presta valves
are much better for bikes than Schraeder (car-type) valves,
partly because of this specific issue. Switch to presta if
you are using Schraeder now. -tom
\_ Force required to pump = cross section of pump * pressure
Volume pumped = cross section * length
Max achievable pressure = Your strength / cross section of pump.
So you can see the only way you can get a high volume and a low
force requirement if to have a pump change diameter as pressure
increases. This is not a practical design.
\_ It's not impractical at all. One simple way to do it is to have
two chambers in the pump. Use both of them for high volume/low
pressure, or one chamber for low pressure/high volume. In case
you missed it, there are mini pumps on the market that
incorporate such a feature. There's no real point in putting
it into a floor pump since good floor pumps are so much easier
to use.
\_ My favorite floor pump is the Topeak Joe Blow Pro; I find it quite
easy to use to inflate my 120psi tires. To give you another data
point, I'd avoid the Silca Super Pista (people rave about how
serviceable it is, but it requires a lot of force, and you have to
hold the head on the valve, so you're left inflating with one hand). |
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