Vauclain compound

Vauclain compound Engine 618 of the Canada Atlantic Railway
Baldwin Works high-speed 2-4-2 locomotive
WAGR Ec class showing typical application of Vauclain compound system; note connection of both cylinders to crosshead and the valve chamber inboard of the high-pressure cylinder

The Vauclain compound was a type of compound steam locomotive that was briefly popular from the early 1890’s to the mid-1900’s. Developed by the Baldwin Locomotive Works, it featured two pistons moving in parallel, driving a common crosshead and controlled by a common valve gear using a single, complex piston valve.