Union Pacific 4-12-2 9000-Class

In the 1920's Railroads began seeking ways to move heavy loads at a much greater rate of speed. Up until that time, many companies used Mallets, the first articulated locomotives, which were known for their power, but often had top speeds of little more than 20 mph. The early articulated locomotives such as the mallets had problems with stability at higher speeds and so locomotive builders sought to increase power and speed by building 3 cylinder locomotives on a rigid frame. The idea of the 3 cylinder locomotives was not a new, however locomotives had been steadily increasing in size to a point that they could no longer grow in size due to the forces exerted by the larger cylinders and without breaking or cracking the frames. In the early 1920s the idea of using 3 cylinders came to the front of US builders minds. One of the advantages of 3 cylinder power is a more even distribution of cylinder thrust. With a standard 2 cylinder locomotive, there are 4 "power pulses" per revolution of the bogeys and with a 3 cylinder locomotive you get 6 pulses per revolution. The reduced rail pounding, wheel slip and in general provided a more smooth ride to these locomotives as the running gear and bogeys seemed to be more balanced.

Union Pacific and Southern Pacific approached Alco with the idea of building a high speed freight locomotive. Until that time 2-10-2 locomotives for both the Union Pacific and especially the SP where the main high speed freight locomotives. The idea was to increase the size and power of this design by transforming it into a 3 cylinder locomotive. The third cylinder for this locomotive was located between the frame and was connected to a cranked axel on the second set of driver wheels. The 3rd cylinder was set at and 8 degree inclination that allowed the main rod and cross head of the 3rd cylinder to clear the axel on the first set of drivers. It was decided that the best way to operate the valve gear for the third cylinder was to use the Gresley Valve gear which was invented by the British Locomotive builder, Nile H. Gresley. This valve gear consisted of 2 rocker arms that were attached to the extending valve stems of the outside cylinders and sat on the front of the locomotive. The inverse sum of the motion of the two outside cylinders created the proper motion for the valve of the 3rd cylinder. The additional weight of the Gresley Valve Gear on the front of the locomotive necessitated a 4 wheel leading truck and results of these designs was a locomotive with a 4-10-2 wheel arrangement. The Union Pacific ordered one for testing and it was given the road number 8000.

This locomotive was delivered to the Union Pacific in 1925 and underwent extensive testing and it was quickly determined by the Union Pacific design department that in order to take full advantage of the 3 cylinder design and power an even bigger locomotive would be required. The designers at Union Pacific quickly began working day and night working in conjunction with the builders at Alco to come up with a new design based data collected from #8000. The idea was to add one more axel or set of drivers and the results of theses discussions and design was a 4-12-2 locomotive.

The new wheel arrangement of 4-12-2 were given road numbers starting with 9000. These road numbers are believed to have been used because there are 9 wheels on each side of the locomotive and the locos were often referred to as the "9s". The first locomotive, #9000, was delivered in April 1926 after only a few months of designing and a mere 4 months on the erecting floor. The locomotive immediately began testing and it became apparent that the loco could do everything it was designed to do and the Union Pacific took a liking to this locomotive as it represented "Big Power", one thing the Union Pacific always prided itself on, and the company bought 87 more locomotives of this type over the next four years. Later this design became know as the "Union Pacific Type" locomotive as it was the only company to use this wheel arrangement.

The 9000s quickly replaced the 2-8-8-0 mallets that the Union Pacific had been using which could only travel at speeds of 25 mph. The 9000s could pull the 100-125 freight cars that were previously pulled by the mallets at speeds of 50 mph or better and could do it 80% more efficiently. These locomotives were the main workhorses over Union Pacific mainline from Cheyenne to Ogden until the debut of the Challengers and Big Boys.

The 88 locomotives owned by the Union Pacific were all built by Alco in Schenectady, New York and were delivered in 5 separate orders from 1926-1930. The first order, UP-1 consisted on locomotive #9000. The second order, UP-2 consisted of locomotives 9001-9014, all delivered in 1926. UP-3 consisted of locomotives 9015-9029 and numbers 9700-9707, which were delivered in June and July of 1928. The 8 locomotives numbered 9700-9707 were ordered for the Union Pacific subsidiary Oregon Washington Railroad & Navigation Co. and were used on this branch line until 1929. At that time they were resold back to the Union Pacific and renumbered 9055-9062. UP-4 consisted of numbers 9030-9054 and were delivered from June through October in 1929. The final order was for numbers 9063-9087 and these locomotives were delivered in July and August of 1930.