Quote Originally Posted by Lisa S.H.
I've also heard that one should occasionally replace the rubber end on the Presta pump valve- that it does wear with use and won't form a good seal after a lot of use.
It's just a rubber grommet and easy to replace. I've had them last 10-20 years however. Also if your pump head just screws down on the grommet, it makes a difference how tightly you screw it down. Too tight and the hole in the grommet gets smaller and may hold the valve open even when you're not pumping so that all the air leaks out. Too loose it may not seal well. If you're having trouble with your pump seal, try tightening or loosening the chuck head over the grommet.