Desmodromic Valve

A desmodromic valve is a reciprocating engine valve that is positively closed by a cam and leverage system, rather than by a more conventional spring.

The valves in a typical four-stroke engine allow the air/fuel mixture into the cylinder at the beginning of the cycle and exhaust gases to be expelled at the end of the cycle. In a conventional four-stroke engine valves are opened by a cam and closed by return spring. An engine using desmodromic valves has two cams and two actuators each for positive opening and closing without any return spring.