The Presta valve is a valve (commonly) found in high pressure "road" style bicycletyres. It consists of three major components: the valve body; the valve stem; and the valve cap. In order to accommodate different rim wall depths, the valve body is available in two sizes; standard and extra long. Like the Schrader valve, air pressure inside the tire holds the valve shut; however, unlike the Schrader valve, there is no spring to assist in keeping the valve shut. Instead, the valve can be shut by screwing the valve cap down the threaded valve stem, thus allowing for open and closed valve positions. In addition, the Presta valve is of much smaller diameter than the Schrader valve. These features make the Presta valve a better choice for smaller quantities of air at higher pressure, compared to the Schrader valve which is better for higher quantities of air at lower pressure. A Presta valve requires a different chuck on the bicycle tire pump than the bigger Schrader valve that is used on lower pressure bicycle tires and car or truck tires; simple threaded brass adapters are available to allow a Presta valve tube to be inflated by a pump or air chuck designed for Schrader valves. Common Types of Valves Used for Bicycles (http://www.geocities.com/cyqlist/valve.html) A valve is a mechanical device that regulates the flow of fluids (either gases, fluidised solids, slurries or liquids) by opening, closing, or partially obstructing various passageways. ... Pressure is the application of force to a surface, and the concentration of that force in a given area. ... This racing bicycle is built using lightweight, shaped aluminum tubing and carbon fiber stays and forks. ... Firestone tire A tire (US spelling) or tyre (UK spelling) is a roughly toroidal piece of (usually) rubber placed on a wheel to cushion it. ... Categories: Stub | Bicycle parts ... Categories: Stub | Bicycle parts ...
Prestavalves are more often found on high performance bicycles with narrow rims and tires.
The Prestavalve's stem can be locked in the closed position by screwing down the knurled nut at the top.
In the photo to the left are two different types of Schrader valve cores, a "long" core which has a relatively large exposed spring, and a "short" one with an internal spring that isn't visible.
Shraeder and presta are the types of valve stems used on innertubes.In the U.S., shraeder valves are used on everything from cars to bicycles, so it's a common style.
However, prestavalves are common in Europe, and found on sew-up tires and ultra-lightweight clincher tubes that need an aerodynamic, lightweight valve-stem, such as higher end bikes.
A common question with prestavalves is whether or not it's important to install the valve nuts (knurled metal rings that are used with threaded valves).
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