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A presta valve on some brands have removable valve cores. If the pump is good, and the tube is not punctured, then there are 2 more options: The removable core is not seated properly, and needs to be tightened with a valve core tool. The valve core is bad/leaking, and should be replaced. If it is removable, replace the core only. If it is a one piece ...


Perhaps its obvious, but maybe the tube has a leak? Is it an old tube that has perished and is just letting air out as fast as you pump it in? Perhaps try taking the tube off the wheel, put it in a bucket/tub of water, and then pump. Can you see bubbles somewhere?


If you hear air leaving the pump and it is not going in the tire then you don't have a seal. If you have a seal and valve is blocked then you would not hear air leaving the pumpt


I always save the core out of blown tubes and have never had them not compatible. At the bike store you just see one jar. Might someone come out with non-standard - it could happen.

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