Originally Posted by
subgrade
I have a suspicion that the 'pumping tube' can never have a higher pressure than the tire itself.
Sort of. I assume the thin tube running through the middle (?) of the tire is fairly small. The squeeze from the tire can locally be higher pressure than the gross pressure of the tire, which is much larger volume. This can work in using that method. It's not intended to refill a tire after being patched, or running out of air because of an actual puncture or leak. It's only going to be capable of small volume, which means maintaining, or inflating a
slightly under-inflated tire.
It's the same idea behind a hydraulic lift similar to what's used for cars. You have a small pump making fairly moderate pressure, but it moves a lot of liquid (slowly) over time. You can lift a car with only 10 psi, it just takes a large area.
