Originally Posted by
cranky old road
Since the valve has no spring, as noted, air will leak out if there is not sufficient pressure in the tube to keep it closed. If it leaks out after the tube is pumped up to pressure, then there is a problem. ( I really need to refresh pages before responding and avoid answers that have been rendered superfluous)
The cracking pressure…i.e. the pressure needed to keep a check valve closed…of a presta valve is extremely low, in the range of 1 to 2 psi. Even a small amount of air in the tube will seal it up so leaking from the valve shouldn’t happen.