Originally Posted by
cyccommute
It is relevant. 44.5mph already ruled out the pump...
A tube valve is absolutely required to put pressure into the tube. More importantly, it is necessary to keep the pressure in the valve. Prestas have to be forced to open and they close easily. Any "in and out" of the air in the tube is due to the valve not operating properly or because it is damaged. If the core is loose, it could leak around the bottom of the core. If the stem is damaged...pulled out of the tube...it will also leak. Given the description, my money is on the stem being damaged and 44.5mph just didn't notice it.
44.5 did try another pump, but this was likely operator error or some other problem. Pumps have check valves so the valve is not necessary to act as a check valve - it might make pumping less efficient for presta valves, but you can still get air in to a tube without the valve functioning... it will all escape as soon as you take the pump off, but it goes in in the first place.
Here is a link to a hack/bodge segment of a GCN video I saw yesterday.
Malfunctioning valve that would let the pressure out when the pump was removed, so the pump was left in place for the ride home., essentially relying on the check valve in the pump to put the air in and keep it there.
Edit: If the video starts from the beginning, go to 24:24 to see what I am talking about.