Steam Engine Train
Union Pacific Steam Engine # 9000 - Only one type of this 4-12-2 steam engine was built: the Union Pacific Railroad's 9000-series or class of locomotives. ALCO had obtained permission to use the conjugated valve gear invented by Sir Nigel Gresley. This system used two hinged levers connected to the outer cylinder's valves to operate the inner cylinder's valve. The 9000 class locomotives were the largest to use the Gresley gear feature.