Along with Schrader valves, Presta valves are among the most common valve designs used for bicycle tires. The Presta valve can generally be found on mid- and upper-level road and mountain bikes. Having no valve spring to overcome, the Presta valve uses less energy to pump, while its slender design requires only a small hole in the rim (a smaller hole does less to undermine the cross-sectional strength of the wheel). To determine whether your bike's tires need to be inflated, you should periodically measure the tire pressure.
Unscrew the protective plastic cap from the valve stem and set it aside. Loosen the nut at the tip of the valve stem.
Screw a Presta valve adaptor onto the valve stem. Turn it clockwise until it is firmly seated. This adaptor allows you to use a Schrader-style pump or pressure gauge in conjunction with a Presta valve.
Fit the head of a tire pressure gauge onto the valve adaptor. The pressure gauge will indicate the current tire pressure.
Remove the tire pressure gauge from the valve stem and unscrew the valve adaptor. Turn the nut at the tip of the valve stem clockwise to seal off the valve. Replace the protective plastic cap.