Originally Posted by
eduskator
I've always been under the impression that the length of the ''pin'' increases over time of pumping and pumping. Is it just in my head or is it what's actually going on?
That's just in your head.
The part of the pin that people see, with the little barrel nut on it, is just there to prevent you from accidentally pushing it down and releasing air when the barrel nut is tightened down. It doesn't actually seal anything. In a Presta valve nothing holds the valve closed except the pressure in the tire (on a brand new tube, the valve isn't held in the closed position until you put enough pressure in the tire to press it against the opening and it seals.)