The Baldwin flexible beam engine was a six-wheel steam locomotive which was built by Baldwin in the United States in the mid 19th century. It had a steel firebox and advanced valves and valve gear, which was the equipment used to regulate the admission of steam into the cylinders. This type of locomotive was used on the Pennsylvania railroad. It represented a significant portion of Baldwin's production from the 1840s to the 1860s.
M. W. Baldwin received U.S. Patent No 2,759, on August 25, 1842, for the flexible beam truck locomotive. This unusual engine type delivered great tractive power by placing its full adhesive weight on drivers, while featuring a sufficiently flexible wheel base to negotiate track conditions. This type of locomotive adapted very well to curved portions of the railroad. The truck (the chassis containing the wheels) was fitted with a pair of forward axles. Thus, the first four wheels worked both as drivers and as guides.
Unlike bogie truck, such as the leading truck designed by John Jervis in 1832, the Baldwin's leading flexible beam truck enabled the driving axles to slide back and forth laterally while remaining parallel to each other and the axle located on the rigid wheel base. It was very important to ensure that the powered axles remained parallel to each other to avoid difficulties with the connecting rods that powered the drive wheels. It was only necessary to allow for slight parallel movement of the front axles in order to give a locomotive necessary lateral flexibility.
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| Above, Baldwin's locomotive No 216, which was built in 1861. This was one of Baldwin's six-wheel, flexible-beam truck engines. |