Valve stem

Valve stem

A valve stem is a self-contained valve which opens to admit gas to a chamber (such as air to inflate a tire), and is then automatically closed and kept sealed by the pressure in the chamber, or a spring, or both, to prevent the gas from escaping. They are most commonly used on automobile and bicycle wheels, but also for other applications.

Types

Schrader

Schrader valves are classified by their material, shape, length, and diameter of intended mounting hole (nominally between 8 mm and 16 mm).

Presta

Presta valves are normally only used on bicycles. The stem has a narrower diameter (nominally 6 mm) than the thinnest (nominally 8 mm) Schrader type, and so the bore of the hole in the rim through which the stem passes can be smaller.

Dunlop (or Woods)

Dunlop valves were once popular in Great Britain and Asia. They are still widely used on 28- and 27-inch tires in many countries (the Netherlands, Germany, Third World) on single-speed bikes for comfort riding in flat terrain.

Their bases are wider than Presta valves, but they can be pumped with Presta pumps. Pumps with a pincher-type connection however are the most common type used: the classic black pumps mounted on a wooden base. The classic pump does not allow for high pressures, 3.5 bar (50 psi) max.

Due to the construction, the Dunlop valve does not check the pressure. The actual valve can be replaced easily, without the need for special tools as with Schrader valves. This also allows use of a wide stem to fill the tube with a sealant that cures leaks while cycling.

Invisible valves

Invisible tire valves are different in design from traditional tire valves. An inflator stem is not used; instead, a removable cap on a valve stem embedded in the tire rim is fitted, with only the cap visible. When inflating the tire, the cap is first removed, typically with a coin, and then a "portable" dedicated inflator stem is screwed onto the valve stem. Through the inflator the tire is inflated as usual. Invisible valves are simple in appearance, and by removing the inflator stem can improve the balance of whole tire. Currently invisible tire valves are popular in Europe. Recent designs simplify use with some caps designed to be removed by the inflator stem itself.

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