Valve stems allow inflation of tires or tubes and can be standalone or connected to an internal tube. The Schrader valve is common on cars, while the Presta valve is used on bicycles. They can also be used on pressurized mechanisms like shock absorbers and air conditioning units.
A valve stem is generally a cylindrical piece of metal that protrudes from an inner tube and through a wheel to allow a user to inflate the tire or tube. The valve stem may or may not be connected to an internal tube; instead, it can be a stand-alone unit that allows air to pass directly into a tubeless tire and wheel setup. In many cases, the valve stem will close on its own in many cases to prevent air from escaping once the inflation process is complete, although some stems must be manually sealed.
The most common type of valve stem is the Schrader valve, which is common on cars, motorcycles, and even bicycles. It is sometimes referred to simply as a car tire valve because it is more recognizable as being used on car tires. The valve stem is usually threaded on at the tip to allow a plug to be screwed on; This cap prevents dirt and sand from entering the valve, thus blocking the air passage or causing an air release. The valve stem core can usually be removed by unscrewing it from the stem barrel, although core removal is not usually necessary. The core prevents air from escaping from the valve stem, and when pressed, opens the chamber to allow air to pass into the tire or tube during the inflation process.
Another common type of valve stem is the Presta valve, which is most commonly used on bicycles. This type of valve is much narrower than a Schrader valve, and the core is a different design than a Schrader valve as well. The core is placed inside the stem barrel, but is pressed open or closed using a threaded barrel that extends past the tip of the valve barrel. When unscrewed, the barrel allows air to pass through the barrel, and when screwed down tight, it seals the chamber. These valves are not common in other applications beyond bicycle tire and tube setups.
Tires and tubes aren’t the only application for valve stems. They can be used on almost any pressurized mechanism; Some automobile shock absorbers, as well as motorcycle and bicycle shocks, may feature these valves to allow customization of shock responsiveness. Air conditioning units sometimes have these valves, as do some mechanisms associated with plumbing applications.
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