The Schrader Valve on a Bicycle Tire

Also called an American valve, the Schrader valve is the familiar valve found on most pneumatic tires used on cars, motorcycles, and on many bicycles throughout the world. It is named after the company owner who developed it, August Schrader.

The Inventor

August Schrader (1807 to 1894) was a German-American immigrant who began his career by supplying fittings and valve parts to the Goodyear Brothers company. After becoming interested in diving, he created a new copper helmet, which eventually led him to design an air pump for use in underwater applications. 

When pneumatic tires began to become popular in 1890 for bicycles and automobiles, Schrader quickly saw the opportunity for developing a valve for those tires. Patented in 1893, shortly before his death, the Schrader valve was his greatest achievement and remains in use today in virtually the same form.

The Structure of a Schrader Valve 

The Schrader valve is a simple device, but one that depends on precise machining of the brass components. The valve consists of an outer stem into which fits a spring-loaded inner pin that seals against the bottom opening of the outer stem with a rubber washer seal. The top of the outer stem is threaded to hold a cap that protects the pin and prevents tiny air leaks. When an inflation device is attached to the stem, the inner pin is depressed downward against the pressure of the spring to open the valve for the passage of air. 

Although most commonly used on tires, the Schrader valve is also seen on some other kinds of air tanks, such as scuba tanks and also on some hydraulic equipment. Modern versions of the Schrader valve incorporate electronic sensors that allow the valve stems to work with Tire Pressure Monitoring Systems (TPMS).

The standard threading on Schrader valves means that they can be filled with just about any of the standard air-pump equipment found at gas stations. It is also the fitting found on most standard air pumps, such as the ubiquitous bicycle hand-pump.

Although Schrader valves are the standard for children's bikes and entry-level adult bikes, higher-end bikes that use higher air pressure generally use Presta valves. Presta valves use a thinner stem than is found on the Schrader valve (about 3mm vs. 5 mm), which makes it suitable for the very narrow, high-pressure road-racing bike tires. To use Presta valves with standard air pumps, an adapter is needed. Or, there are also air pumps with duel fittings that can be used with both types of valves. Unlike the spring-loaded pin that opens and closes a Schrader valve, the Presta valve has a knurled cap to keep it shut.