Presta Valve (also known as French Valve ) is a pneumatic valve for bicycle cameras. It is mainly used on road, hybrid and other bicycles with a thin wheel rim. Has a screw locking nut that secures the valve in the closed state. It is possible to use a screw-tight, dirt-proof cap (compatible with caps on Dunlop valves ).
Since usually the weakest point of the rim is the hole for the valve, a smaller diameter (6 mm) compared with other valves allows you to reduce the width of the rim of the wheel without significantly weakening it [1] . The valve itself has a free stroke of about 2 mm, but when pumping it is locked from the inside by increasing pressure.
The rims intended for this valve can be adapted for other valves by widening the hole to 8 mm, however this will weaken it to a certain extent. At the same time, it is possible to adapt the rims intended for other valves by placing a special adapter or a makeshift lining in the valve hole [1] .
Used adapters for automobile pumps ( Schrader valve ) must have a rubber seal, since their short threaded connection to the valve does not allow to effectively contain pressure when pumping.
Advantages relative to other valves:
- Smaller diameter (6 mm), which increases structural rigidity on thin rims of bicycles (hybrid, highway).
- Lighter wheel weight (slightly).
Disadvantages:
- Lower pump prevalence - a high-quality adapter is required for all automotive pumps ( Schrader valve ). Not all compact hand-held bicycle pumps have the option of pumping through this valve as an option.
- In case of inaccurate action during pumping, it is possible to break the valve stem with the impossibility of further operation of the chamber as a whole. In expensive cameras, the valve mechanism can be replaced.
- Clean the valve lock nut with clean hands to prevent dirt from entering the valve mechanism.
See also
- Schrader Valve
- Dunlop valve , also called Woods valve or English valve