Originally Posted by
FBinNY
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.
THAT is some valuable information! Thank you! A few of my tubes have been driving me mad, and I couldn't figure out why. It wasn't until this thread that I had ever heard of "burping" them and this information makes it all very clear.
Thanks again!