The Caprotti valve gear is a type of steam engine valve gear invented in the early 1920s by Italian architect and engineer Arturo Caprotti. It uses camshafts and poppet valves rather than the piston valves used in other valve gear. While basing his design on automotive valves, Caprotti made several significant departures from this design to adapt the valves for steam. Having agreed a joint-venture with Worcester-based engineering company Heenan & Froude from 1938, Heenan & Froude fully acquired Caprotti post-World War II in 1947.
Duke of Gloucester
Caprotti valve gear on BR no. 73129
The valve gear of a steam engine is the mechanism that operates the inlet and exhaust valves to admit steam into the cylinder and allow exhaust steam to escape, respectively, at the correct points in the cycle. It can also serve as a reversing gear. It is sometimes referred to as the "motion".
The Walschaerts valve gear on a steam locomotive (a PRR E6s).
Soo Line 346 in 1961, showing the Kinkan-Ripken arm on the connecting rod at the right hand edge of the picture
Stephenson's Valve gear. Two eccentrics at nearly 180-degree phase difference work cranks from the main drive shaft. Either can be selected to work the valve slide by shifting the slotted expansion link.
Baker valve gear assembly