Old 04-21-19, 12:49 PM
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fietsbob 
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Advantage: Presta valves, only the air pressure differential closes the check valve in the stem .
so you don't have the valve core spring to work against, with every pump stroke.

If, there were there a pin holding the S/V open, it would not retain any air pressure increase,
but push back on the handle.

in a Floor pump there is a check valve in the base,
when you take the pump head off the valve stem , only what's in the hose vents off..
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