removed or tightened with a tool. Industrial Schrader valves are available in different diameters and valve core variants and are used in refrigeration, propane, and a variety of other uses. With the advent of miniature electronics, Schrader valve stems with integrated transmitters for tire pressure monitoring systems (TPMS) became available. Cap A valve cap on a Schrader valve prevents entry of contaminants that may interfere with the sealing surfaces and cause leakage. Metal, and some hard plastic valve caps, have a rubber washer or O-ring inside, both to prevent the cap from loosening and falling off due to vibration. These caps also serve as a mechanical seal to prevent air from leaking from a faulty valve core. Simple caps without a seal do not reliably prevent leaks. Some metal caps are equipped with prongs to enable removing and replacing valve cores, thereby serving two functions: seal and emergency tool. In refrigeration and air conditioning applications, the valve cap is considered to be the primary seal, with the Schrader valve only being used for service access. Schrader versus other valve types There are three valves used on tires worldwide: Schrader valves, Presta valves, and Dunlop valves. Each goes by multiple names. Schrader valves are also known as American valves or car valves. Presta valves are also known as French valves, Sclaverand valves, and road bike valves. Dunlop valves are also known as German valves, English valves, Holland valves, Woods valves, flash valves, and alligator valves. Schrader valves are almost universal on car, truck, and motorcycle tires worldwide. Presta and Dunlop valves are mostly found on bicycle tubes. Both the Schrader and the Presta types are effective for sealing high pressures. Their chief differences are that Schrader valves are larger and have springs that close the valve except when the pin is depressed. Schrader valves are used in a wide variety of compressed gas and pressurized liquid applications such as small torch and grill cylinders, and air shocks. Schrader valves are also viewed as more complex (requiring two seals over one). They weigh 4–5g more than Presta valves. Schrader and Dunlop valve stems are 8 mm in diameter, whereas Presta valve stems are 6 mm, allowing Prestas to be used on narrower, high-performance rims as on road racing bicycles. Another disadvantage of the Schrader is that debris may be introduced into its spring-loaded pin, impairing inflation, whereas the Presta valve relies only