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Big Boy 4-8-8-4
40.51 m Total length 132 ft 9-7/8 in
13.90 m Tender length 45'6"
346 t Locomotive's serviceweight 762,000 lb
194 t Tender's service weight 427,500 lb.
540 t Total weight 1,189,500 lb
5,884 kW Power 8,000 hp
Tractive effort 135,375 lb
2 D, D 2 Wheel arrangement 4-8-8-4
30.6 t Driving axle load 67,500 lb
1.73 m Driving wheel dia. 68 in
1.07 m Truck wheel dia. 42 in
20.67 bar Boiler pressure 300 psi
13.96 m2 Grate area 150.3 ft2
25.4 t Coal 28 tons
94,750 l Water 25,000 gal
128 km/h Maximum speed 80 mph
64 km/h Normal speed 40 mph
Home for the 25 Big Boys was the 432 miles of the Union Pacific between Ogden, Utah and Cheyenne, Wyoming.At 1.14% both of the ramps to the high prairie of Wyoming offered the greatest grades: Going east the Wasatch Mountains between Ogden and Evanston, and in the opposite direction going west, Sherman Hill between Cheyenne and Laramie.

The USA around 1940: The rail route between Ogden, Utah and Cheyenne, Wyoming is one of the most heavily traveled routes on the Union Pacific network.From the West Coast came fast Pacific Fruit Express trains, in the opposite direction coal and ore trains.The middle part of this route runs cross the over 6,500 foot high plateau in the state of Wyoming.The bottlenecks on this route are the 1.14% steep ramps - in the west the Wasatch Range, in the east Sherman Hill between Cheyenne and Laramie - very heavy work for the steam locomotives.Locomotives were kept constantly under steam for "pusher service".Sometimes up to four locomotives were required for a freight train.This work was complicated, time-consuming and expensive.The Union Pacific therefore gave the American Locomotive Corporation (Alco) an order for a locomotive that would be powerful enough to pull 3,600 ton freight trains on its own.The required trainload and the maximum axle load resulted in the 4-8-8-4 wheel arrangement.After only a year's development work they came up with a steam locomotive that surpassed everything that had come before it in the sum of its characteristics and power and that was never achieved again: The class 4000 - called "Big Boy".The first class 4000 locomotive was placed into service in 1941 right after the first test runs.The units numbered 4001 through 4019 followed, and units 4020 to 4024 came in a second series in 1944.

These locomotives even surpassed the performance parameters and were able to haul trains of up to 4,200 tons.It's hard to believe that these 164-foot monsters could run at speeds up to 80 mph.This top end speed was, however, only a calculated powered reserve.In regular operation it was a bit more sedate: A Big Boy required around four hours for the 75 miles from Ogden up the mountains to Evanston.It ran at a speed between 15 and 40 mph and used up almost its entire fuel capacity in the process.At least three stops to take on water and coal were required during a run, depending on the trainload.Often the Big Boys handed their trains off to other locomotives on the high prairie, because the rest of the run required less power.In their last years of service, the range of the Big Boys was reduced to those parts of the route with steep grades.The locomotives were turned on immense turntable in Laramie and Evanston.The Big Boys became a symbol of American railroading due to their dimensions, power and the high level of reliability for all 25 locomotives.Every locomotive in the first series achieved a road mileage total of more than a million miles, the second group over 800,000 miles.Numerous photographers and steam locomotive fans said farewell to an era and a legend when the last Big Boys were in service on Sherman Hill in 1958.

Fully loaded, the tender weighs around 214 tons or 194 metric tons and rides on seven axles.Two axles are in the leading truck, the others are mounted in the frame.The tender's capacities are 28 tons or 25 metric tons of coal and 25,000 gallons or 95 cubic meters of water - immense quantities that were enough for two to four hours of operation.Such quantities of coal were not simply shoveled through the firebox door; a mechanical stoker took care of this.The coal slides down the hopper-shaped tender floor into a transport channel.There a transport screw pushes it to the locomotive.It is simultaneously crushed and finally distributed into the firebox.The fireman, however, does not have an easy job when the locomotive is called upon to provide its full power.

The cab for the Big Boy is about the size of a small cabin and is extensively glassed in.In addition to the locomotive engineer, fireman and brakeman, a reserve crewmember can also ride here.The controls and gauges are those of a normal steam locomotive.

The Big Boy has another size record in order to keep its immense boiler at full steam.With an area of 150 square feet or 14 square meters, the grate is the size of a bedroom and heats up to a temperature of around 800 Celsius (1,500 F).With this kind of heat the fireman must be very careful that the firebox is constantly surrounded with water, even on grades, so that it does not overheat.

Four cylinders power the two groups of driving wheels.Yet, the Big Boy is not a Mallet locomotive that you would be familiar with in Europe.There are no high and low pressure cylinders linked with one another; both cylinder groups draw their high pressure steam directly from the boiler.This increases the power, but also the consumption of coal and water.

The rear group of driving wheels with its frame is rigidly mounted in the frame for the locomotive.The front group of driving wheels including the cylinders is attached by an articulated joint to the rear group of driving wheels and can swing out on curves.The frame for the front group of driving wheels supports the weight of the boiler by means of a sliding bearing and brings weight to bear on the axles for more traction.Suspension springs even out differences in the height of the track.The weight distribution on both groups of driving wheels was so successful that the locomotive rarely experienced wheel slip.The steam lines are flexible and specially sealed to supply the two front cylinders with steam.
Despite the Big Boy's length, its articulated frame makes it very maneuverable on curves.It's an impressive sight when the front group of driving wheels including the pilot superstructure, pilot truck cylinders and driving wheels swings out on curves.

The part of the boiler set off in silver colored paint is the smoke box.The immense amounts of steam and smoke require two smoke stacks to produce enough draft for the Big Boy.Smoke deflectors that can be adjusted from the cab keep the latter from being fogged in.

The front truck guides the first group of driving wheels into a curve and thereby improves the running characteristics.The heat exchanger for air-cooling is placed on the pilot superstructure.

A total of 25 Big Boys were built in 1941 and 1944.They were in use for around 20 years and each one ran over 1 million miles.In 1959 the last Big Boy was used to haul a regularly scheduled freight train.A couple of the locomotives were kept in running condition until the final end came in 1961.Eight locomotives still give an impression of their size.Only three of these museum locomotives are technically capable of being restored to operating condition.Several groups of interested people are considering the restoration of one these historic giants.

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