You will see Presta valves on most road bike tubes, including tubular or “tubeless” tires. Presta valves are long and skinny, with a nut on top that protects the depressible valve pin from moving and leaking air. A ring-shaped nut screws onto the body of the Presta valve and holds it firmly in place against the rim for easy inflating. Presta valves do not need to be capped, though they do come with a cap meant only to protect the inner tube from the sharp edges of the valve when the tube is rolled up.
Schrader valves, seen on mountain bikes, kids’ bikes and all types of casual riding bikes, are the same valve type you will see on automobile tires. The valve body is shorter than that of a Presta, and the depressible pin sits inside the valve stem rather than on top of it. The valve also contains a spring-loaded core that prevents air leakage when the pin is not pressed. Schrader valves should be covered with the cap that accompanies each inner tube to protect the inside of the valve from dirt, debris and water.
Woods or Dunlop valves have characteristics of both Schrader and Presta valves. Though the base of the valve is similar in width to a Schrader valve, the top part is similar in width to a Presta valve. A ring screws onto the valve body to hold it against the rim, just like a Presta valve. Unlike the Presta valve ring, however, the Woods or Dunlop valve ring forms an airtight seal between the valve and the tube. The valve ring must be airtight because the valve itself isn’t; it is replaceable and you can move it from a worn-out tube to a new tube.