Allman horizontal engines were built in several sizes from 2 to 15 horsepower. The block shown on the flywheel hub served as both a counterweight and a governor housing. Through a linkage system, the governor accurately controlled the engine at any desired speed. Inverted vertical engines were built in 2, 3, and 4 horsepower sizes by the Allman & Thompson firm. A little 3/4 horsepower inverted vertical was also built – this model differed little from its larger brothers except that a wedge action governor system opened the exhaust valve partially or fully depending on the speed. All other Allman engines used the same governor principle but applied it to the intake valve.