Between 1928 and 1930 the Union Pacific Railroad ordered 88 locomotives from the American Locomotive Company, otherwise known as ALCO, for use on freight trains with the intended purpose of making these freight trains move faster. How did they go about with this? Stream lining? Building massive articulated mallets? No. Instead they built a 3 cylindered engine that used Conjugated Valve Gear, which was invented by Sir Nigel Greasly (the cheif mechanical engineer of the LNER over in Great Britain), and was a non-articulated 4-12-2 type locomotive. These massive engines were known as the Union Pacific 9000 class.
The UP 9000 class was impressive in multiple ways. First of all holding the record for being the only locomotives to ever have the 4-12-2 wheel arrangement, being called the "Union" type after the Union Pacific Railroad, and for having nearly 100,000 lbf of traction effort. However, these machines were plagued by mechanical short bringings. They were maintenance nightmares, largely because of their use of an inside third cylinder driving the cranked second driving axle between the frames. The Conjugated Valve Gear also gave mechanics problems, so much so that between 1934 and 1940 eight of the first fifteen locos had their Gresley gear removed and were converted to a "double Walschaerts" valve gear which utilized a double eccentric (return) crank and second link on the right side, which operated the valve for the inside cylinder. Union Pacific referred to this system as the "third link." The 4-12-2's constructed from 1928 utilized roller bearings in the Gresley lever bearings, thus none of these engines were converted. The pre-1928 engines not converted received the roller bearing levers in 1940, and no further conversions were made. Not only did their inability to be worked on a issue but the fact that they were non-articulating and so long limited their route availability; they were only able to run on track that was straight enough not to derail the engine or damage the track it ran on. Only one example has survived into preservation. Union Pacific No. 9000 is preserved at the Railway and Locomotive Historical Society's museum at the Los Angeles County Fairplex in Pomona, California.
