Doohickie

Yeah, if you have a Presta valve and are used to Schrader valves (like what they have on cars), there is a little different techinque to filling up a tire.

On a Schrader, a spring seals the valve to keep air from escaping. To pump up a Schrader valve, you have have a pump head that pushes the valve open (by pushing on the little metal piece in the middle). You have to make sure the pump head has gone on far enough to push that piece.

With a Presta, there are two things holding the valve closed: 1) there is a little knurled nut on the end of the plunger that holds the plunger in the closed position. You have to loosen that nut (it's on the tip of the valve, under the plastic valve cap). 2) Any air pressure in the tube will also push the valve shut. Or in some cases, the valve is stuck shut just because it hasn't been opened in a long time. So once you loosen the knurled nut, it's a good idea to tap the end of the valve to make sure the plunger moves and the valve isn't stuck. One thing you don't have to do, though, is hold the valve open (like with a Schrader valve). As long as there is more pressure outside the valve than inside, the valve will open to allow air in.

So... to fill a Presta valve tube:

1. Remove the plastic valve cap.
2. Loosen the brass knurled nut on the end of the valve plunger.
3. Push the plunger in to make sure the valve isn't stuck.
4. Line up the pump head and push it over the valve; you don't have to push it "all the way" to depress the valve though.
5. Lock the pump head in place.
6. Pump up the tire.
7. Release the pump head and remove the pump from the valve.
8. Tighten the knurled nut on the end of the plunger.
9. Put the plastic valve cap back on.

It's not really as complicated as nine steps would indicate, but if you're accustomed to automotive style Schrader valves, Presta valves take a little getting used to. When I first started with them, sometimes I would forget to loosen the knurled nut; other times I tired to push the pump head onto the valve far enough to push the plunger. Neither of these methods led to success. I was convinced the pump was broken. Once I did it right it occurred to me that I was trying to fill it like a Schrader valve. Duh.