Presta-Valve Basics - Before you can put air in a Presta valve, you must remove the plastic valve cap (if there is one) and unscrew the very tip of the valve. Look closely and you'll see that the valve's tip is knurled to make it easy to turn by hand. Unscrew it (counterclockwise) and then press the tip down until some air escapes. This is important because it frees the valve, which usually sticks after being sealed for a while. Until you free it, it can be difficult to impossible to put air into the valve.