Presta valve stems are typically found on high-pressure road bike tyre tubes. They are different from the more traditional Schrader stem in size and length. Additionally, Presta valves are threaded and have a locknut that tightens the stem against the wheel frame. Because of these differences, Presta valves require a pump specially designed for such valves. There are, however, small brass adaptors that can be placed on a Presta valve for use on a traditional bike pump.
Using a Presta pump
Remove the cap on the valve stem. Once the cap is off, you will notice a small nut on the end of the valve itself. This nut prevents pressure loss during riding. Loosen this nut.
Insert the valve stem into the end of the pump and secure it by lifting up the switch on the end of the pump.
Fill to desired pressure. Most tyres will have the proper psi printed on the sidewall of the tyre. To check the pressure, most pumps will have a built-in gauge on the pump. If your pump does not have a gauge, simply use a standard tyre gauge.
Using a traditional pump
Follow Step 1 from the section on using a Presta pump.
Screw the valve adaptor onto the top of the valve stem. Be sure that the nut on the valve stem has been loosened, otherwise no air will enter the tire tube.
Attach the pump. Lock the stem into the pump by lifting the switch.
Pump air to the desired psi. If the pump does not have a built-in gauge, check the pressure periodically with a hand-held pressure gauge.
Many bike shops carry portable Presta valve pumps that can mounted to your bike frame for emergency roadside repairs.