Originally Posted by
Grand Bois
Differential air pressure opens and closes presta valves.
Did I say that right?
yes, you said it right. PV's are simple check valves that open and close so air can enter the tube, but not flow back out.
EXCEPT
That sometime between when the Italians and French made them, and when it all went to Taiwan and China, they messed up on the gasket material so now the valves stick closed over time, and have to be unstuck by manually letting a bit of air out (burping) before they'll work right when you pump.