A compound locomotive is a steam locomotive which is powered by a compound engine, a type of steam engine where steam is expanded in two or more stages. The locomotive was only one application of compounding. Two and three stages were used in ships, for example.
Vauclain four-cylinder compound locomotive Milwaukee Road class A2 No. 919.
Cutaway view of the cylinders (low-pressure on left, high-pressure on right) and valves (above) on a tandem compound engine
Burrell road locomotive, showing high- and low-pressure cylinders.
Francis William Webb was an English railway engineer, responsible for the design and manufacture of locomotives for the London and North Western Railway (LNWR). As the LNWR's chief mechanical engineer, he also exercised great influence in political and public life in the Cheshire town of Crewe, once being described as the 'King of Crewe'.
Webb in 1890
No. 1881 Class B locomotive of the London & North Western Railway, a Webb 0-8-0 four cylinder compound.