Schrader Valve:
The Schrader valve consists of a 8mm diameter stem into which a valve core is threaded. The valve core is assisted by a spring, this is called a check valve that is meant to allow airflow in only one direction; the Schrader-valve tube requires pressure on the inner pin to let air in. If the valve core is faulty, it can be extracted and replaced using a schrader valve core tool.
Presta Valve:
The Presta valve stem is 6mm in diameter and there are different lengths to allow for rims with a deeper section but 40mm is a standard length. Just the action of the air pressure holds the inner valve body shut, however, there is also a small screw and captive nut on top of the valve body that ensures that the valve stays closed. In order to permit airflow in either direction, the valve nut must be unscrewed and depressed. We talk more about how to pump up a Presta valve in another one of our articles.
