The Walschaerts valve gear is a type of valve gear used to regulate the flow of steam to the pistons in steam locomotives, invented by Belgian railway engineer Egide Walschaerts in 1844.
The gear is sometimes named without the final "s", since it was incorrectly patented under that name. It was extensively used in steam locomotives from the late 19th century until the end of the steam era.
A set of Walschaerts valve gear on 60163 Tornado. Note that the radius bar is set to reverse.
Swindon, Marlborough and Andover Railway Single Fairlie 0-4-4T of 1878. This was the first British locomotive to be fitted with Walschaerts valve gear
The Walschaerts valve gear on a Pennsylvania Railroad E6s
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