desmodromicvalve

Desmodromic valve refers to a valve actuation system in which both opening and closing of the engine’s intake or exhaust valve are achieved by positive mechanical action, rather than relying on a valve spring to close the valve. In a typical desmodromic arrangement, a camshaft provides separate motion to open the valve and to close it, often via two lobes or two dedicated followers per valve. One lobe drives the mechanism to push the valve open, while a second lobe or linkage drives the mechanism to close the valve, producing a controlled, forceful return without depending on spring pressure.

Mechanism and variations vary by design, but common themes include two opposed cam paths or a close-coupled pair of followers and rockers. Some designs employ a closing follower that retrieves the valve rather than allowing the closing spring to compress. While most desmodromic systems aim to eliminate valve float at high engine speeds, some configurations still use a small spring as a safety backup or to take up slack in the mechanism.

History and use: The desmodromic concept is associated with high-performance engines and has become especially well known for its use in Ducati motorcycles since the mid-20th century, where precise valve control at high RPM is valued. It has appeared in limited automotive applications and racing contexts as an alternative to conventional spring-based valve trains.

Advantages and disadvantages: Proponents cite improved high-RPM valve control and timing precision, while critics point to greater mechanical complexity, weight, cost, and maintenance requirements compared with conventional spring-based systems. See also valve train, camshaft, and overhead cam.