Topic summary
Intake valve
Extracted from the Wikipedia article Poppet valve.
Actuation method
Early engines in the 1890s and 1900s used an "automatic" intake valve, which was opened by the vacuum in the combustion chamber and closed by a light spring. The exhaust valve had to be mechanically driven to open it against the pressure in the cylinder. Use of automatic valves simplified the mechanism, but valve float limited the speed at which the engine could run, and by about 1905 mechanically operated inlet valves were increasingly adopted for vehicle engines.