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Great Eastern class A55 “Decapod”
Great Britain | 1902 | only one produced
A55 together with its developer, James Holden
A55 together with its developer, James Holden
Locomotive Magazine, March 1903
Front view with the Wootten firebox clearly visible
Front view with the Wootten firebox clearly visible
F.S. Hartnell, All About Railways
Rebuilt A55R as an eight-coupled tender locomotive
Rebuilt A55R as an eight-coupled tender locomotive
Railway and Locomotive Engineering, July 1907
Schematic drawing of the A55 with dimensions
Schematic drawing of the A55 with dimensions
Railway and Locomotive Magazine, April 1903
Schematic drawing of the A55R with dimensions
Schematic drawing of the A55R with dimensions
Locomotive Magazine, December 1906

In view of the plans for a new electric line, the Great Eastern tried to counter with a particularly powerful passenger tank locomotive. In order to be able to keep up with future electric railcars, the greatest attention was paid to comparable acceleration in order to achieve a reasonable travel time on the network with many closely spaced stations. Thus it was defined that a passenger train with a weight of 315 long tons must be brought to a speed of 30 mph within 30 seconds. To meet these requirements, James Holden developed a machine of which only a single example was built.

The result was the first ten-coupled steam locomotive in Great Britain, which also had a very small coupling wheel diameter for a passenger locomotive. If two cylinders were used for the required tractive effort, the loading gauge would have been exceeded, so the engine was designed with three slightly smaller cylinders. While the outer cylinders acted on the third axle, the middle cylinder drove the second axle. Since the inner cylinder was also level with the axles, the connecting rod was wrapped around the first axle in a special, fork-shaped arrangement patented by Holden.

The boiler was designed as large as the loading gauge allowed. For this reason, the chimney, the steam dome and the safety valves had to be as low as possible. The Wootten firebox based on the American model allowed a large grate area and had to be divided into three areas because the wheels of the last two axles protruded directly into it. To achieve the necessary running characteristics, the first and last axles were installed with half an inch play on both sides and the middle one had no wheel flanges

Although the axle load of the “Decapod” was within the permitted values, the five axles lying closely behind each other represented too great a load for the bridges. Since upgrading all the bridges on the routes used was not an option, there was no series production of the A55. The locomotive was converted in 1906 to an eight-coupled tender locomotives known as the class A55R.

It got a significantly lighter boiler with a conventional Belpaire firebox and the middle cylinder was removed. Since the length of the locomotive was still large, the axles were spaced farther apart. In order to still be able to run through all curves without any problems, the first and fourth axles were fitted with radially adjustable bearings. This locomotive was now used to haul coal trains, although it did not display significantly greater efficiency than the three-coupled G58 class locomotives. So it was scrapped in December 1913.

Variantas builtrebuilt A55R
General
Built19021906
ManufacturerStratford
Axle config0-10-0T (Ten-coupled) 0-8-0 (Eight-coupled) 
Gauge4 ft 8 1/2 in (Standard gauge)
Dimensions and Weights
Length37 ft 6 in56 ft 11 in
Wheelbase19 ft 8 in23 ft 3 in
Fixed wheelbase19 ft 8 in8 ft 9 in
Service weight179,200 lbs121,716 lbs
Adhesive weight179,200 lbs121,716 lbs
Total weight207,396 lbs
Axle load37,520 lbs35,252 lbs
Water capacity1,300 us gal3,500 us gal
Fuel capacity4,480 lbs (coal)11,200 lbs (coal)
Power
Power sourcesteam
Estimated power1,300 hp (969 kW)925 hp (690 kW)
Optimal speed21 mph25 mph
Starting effort38,788 lbf23,273 lbf
Power Plant
Driver diameter54 in
Boiler pressure200 psi180 psi
Expansion typesimple
Cylindersthree, 18 1/2 x 24 intwo, 18 1/2 x 24 in
Boiler
Grate area42 sq ft22.9 sq ft
Firebox area131.7 sq ft131.4 sq ft
Tube heating area2,878.3 sq ft1,738.6 sq ft
Evaporative heating area3,010 sq ft1,870 sq ft
Total heating area3,010 sq ft1,870 sq ft
Calculated Values
steam locomotive
passenger
freight
tank locomotive
prototype
James Holden
last changed: 09/2022
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