Hub or Crank Mounted Pump

It would be nice to replace the CO2 system with a low flow rate pump
that could charge up a pressure vessel, mounted on the rear hub or
crank.

After you inflated a tire after a flat it might take 3 - 5 miles of
pedaling to refill the tank.


Bret Cahill

"Bret Cahill" wrote: (clip) After you inflated a tire after a flat it might
take 3 - 5 miles of pedaling to refill the tank.
^^^^^^^^^^^^^^^
A road tire is inflated to 7 or 8 atmospheres. If your tank had a volume
equal to the tire volume, it would have to be inflated to about 15
atmospheres by your little pump. You surely want the tank to be smaller
than that! If you made the tank half the tire volume, the required pressure
jumps to 30 atmospheres. That's 450 psi, more or less. It starts to sound
impractical.

The reason a little CO2 cartridge can do the job is that it is filled with
liquid that turns to gas on release, with a large expansion ratio.

They want to store H2 at 10,000 psi in carbon fiber tanks for vehicle
fuel. The problem isn't the pressure vessel but a really light weight
low volume high pressure pump.

It might require a completely different principle than typical 12 v
displacement compressor you buy at Pep Boys for $14.00


Bret Cahill

On 29 Jun 2005 13:53:21 -0700, "Bret Cahill"
wrote:

They want to store H2 at 10,000 psi in carbon fiber tanks for vehicle
fuel. The problem isn't the pressure vessel but a really light weight
low volume high pressure pump.

It might require a completely different principle than typical 12 v
displacement compressor you buy at Pep Boys for $14.00

The inherent work required to compress a gas cannot be reduced below a
certain point by the selection of any novel method. At the pressures
that your idea would require, the weight of the components would be
nontrivial, the precision required in their manufacture would be
considerable, and the cost would likely be exorbitant, particularly by
comparison to existing solutions. But please, don't take my word for
it; by all means, do spend the time, effort and funds to bring this
idea to fruition. Before filing for a patent, however, it would be
wise to research prior filings, as I'm pretty sure that this has been
tried before.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

Quoting Bret Cahill :
It would be nice to replace the CO2 system with a low flow rate pump
that could charge up a pressure vessel, mounted on the rear hub or
crank.
After you inflated a tire after a flat it might take 3 - 5 miles of
pedaling to refill the tank.

Aside from the comments on mechanical plausibility, I find that when
people do get 2 flats on one ride it is often because of a hamhanded fix
to the first flat, and you won't make it 5 miles down the road like that.
--
David Damerell Kill the tomato!
Today is First Friday, Presuary.

In article . com,
"Bret Cahill" wrote:

They want to store H2 at 10,000 psi in carbon fiber tanks for vehicle
fuel. The problem isn't the pressure vessel but a really light weight
low volume high pressure pump.

It might require a completely different principle than typical 12 v
displacement compressor you buy at Pep Boys for $14.00


Bret Cahill

Very high pressure compressors are multistaged pumps, so each little
piston needs only to add so many psi to the gas. Often they have
coolers (or "condensers") between the stages since gases heat up as
they're compressed, which causes them to try to expand again, which
reduces efficiency when pumping. Old diesel engines used to use
compressed air to inject the fuel rather than a hydraulic fuel pump.
Those engines had three-stage piston compressors capable of nearly 1,000
psi. Guys with the dangerous hobby of rocketry actually build their own
oxygen pumps on occasion. Same setup--pistons, multistaged, with
coolers. Just no oil for lubrication; (would blow up) they use
self-lubricating materials like brass on steel. I think they tend to
get into the neighborhood of about 2,000 psi, but I could be wrong.
The little piston compressor pumps at auto stores are just a
single-stage compressor with no cooler. Same basic principal, though.
The idea for a hub-mounted pump to refill tires is probably
doable--the technology is simple enough. You could probably get up to
250-275psi in three stages easily even without any coolers if the
displacement is small. And for a small size, aluminum is a fine
material, so weight shouldn't be too terrible either. Hell, you could
even use plastic pistons, which would be even lighter and
self-lubricating with a good seal and happy with sloppy tolerances.
Storage is another matter, though. Compressed air brings any
humidity with it, and that becomes water once compressed. You'd need a
way to get the water out, like a drain cock, which would get to be more
of a pain than just using a handheld pump in the first place. But still
a neat idea.
Or you could go with an even smaller pump and just rig it up to keep
the tires topped off while you ride. No good for inflating a tire, but
handy for battling a slow leak or simply becoming lazy. With that you
could even get away from wonky plumbing issues and just build a pump
around the outer circumference of the hub with an offset weight dangling
between the spokes to power it. Wheel and pump turn, weight doesn't.
But who wants to add more weight to a bike, anyway?

--
B.B. --I am not a goat! thegoat4 at airmail dot net
http://web2.airmail.net/thegoat4/

Or you could go with an even smaller pump

and just rig it up to keep the tires topped off

while you ride.

The tire goes flat back at the house instead of the road.

Ideally it would engage and disengage at pre set pressures -- no drag
when it isn't pumping.

Something light enough could provide options as far as reducing the
enormous rotational momentum from heavy tubes, tires or leak seal.

A small efficient pump would need to be very ingenious or take
advantage of some novel effect that might have an application in
another industry..


Bret Cahill


"Leave no bad idea behind."

29 Jun 2005 11:50:28 -0700, Bret Cahill:

It would be nice to replace the CO2 system with a low flow rate pump
that could charge up a pressure vessel, mounted on the rear hub or
crank.

After you inflated a tire after a flat it might take 3 - 5 miles of
pedaling to refill the tank.

Not exactly what you are looking for, but at least an air pump inside a
bicycle hub: http://www.nakano-iw.co.jp/e_body/product/product.html

Andreas

On 29 Jun 2005 11:50:28 -0700, "Bret Cahill"
wrote:

It would be nice to replace the CO2 system with a low flow rate pump
that could charge up a pressure vessel, mounted on the rear hub or
crank.

After you inflated a tire after a flat it might take 3 - 5 miles of
pedaling to refill the tank.


Bret Cahill


It's already been done of course, go to this site and put 'F. J. Camm'
into the search box. There's a little bit of work to do to get to the
file to download it but for anyone interested in old time cycling it's
worth it. There's some gems.

http://www.britishpathe.com/index.html