South African Class 21 2-10-4
Encyclopedia
In 1937 the South African Railways placed one Class 21 steam locomotive
with a Texas wheel arrangement in service, designed as a mixed traffic locomotive suitable for light rail. A simultaneously proposed heavier main line version Class 22 never materialised.
(NBL) in Glasgow and delivered in 1937. Only the one locomotive was built, numbered 2551. At the time the design represented the maximum power obtainable from a ten-coupled non-articulated locomotive that was limited to a 15 long tons (15.2 t) axle load on 60 lb/yd rail.
, Class 15F
and Class 23
.
The end result could be considered as Watson’s answer to the Class GF 4-6-2+2-6-4
Garratt locomotive, having very similar weight and tractive capacities. The Class 21 carried more water than the Garratt and was about 23 long tons (23.4 t) heavier with 43700 pound-forces (194.4 kN) tractive effort, compared to the 34200 pound-forces (152.1 kN) of the Class GF. Even so, only one Class 21 was produced and the design was not repeated.
Watson’s design called for cylinders with Rotary Cam Poppet valve gear, but since the locomotive was still under construction when Watson retired, his successor as CME, W.A.J. Day, made use of the opportunity to alter the specifications. Thus, in the year following Watson’s departure, the locomotive was delivered with Walschaerts valve gear.
wheel arrangement with the leading and trailing wheels in bissel type pony trucks and the rest of the axles mounted with a rigid wheelbase. The tender’s wheel arrangement did not prove to be very successful and, with the exception of a similar tender built in the Salt River shops for test purposes, was not used again.
The pony axle design is commonly used on steam locomotives with a single leading or trailing axle, and was also used on the Class 4E
electric and Class 32-000
and 32-200
diesel-electric locomotives.
Texas wheel arrangement, but was to be a heavy main line version of the Class 21, with an axle load of 22 long tons (22.4 t), the heaviest that current SAR track could bear on its 96 lb/yd rail. It was to have been a massive machine with larger 60 inches (1,524 mm) driving wheels, a larger 80 square feet (7.432 m²) grate and the larger Type EW tender that was later to be used with the Class 23
locomotive.
If this locomotive had been built, it may have been one of the world’s most outstanding locomotives. The proposed boiler pressure was 250 pound per square inches (1,723.7 kPa), a figure never attained on the SAR, and its anticipated tractive effort of 66406 pound-forces (295.4 kN) at 75% of boiler pressure would have made it capable of handling loads of 2200 long tons (2,235 t) on the coal run from Witbank
to Johannesburg
with comparative ease.
The design was a compromise between a 2-8-4 passenger class with 66 inches (1,676.4 mm) driving wheels and a 2-10-2 freight locomotive with 60 inches (1,524 mm) driving wheels. At the time, however, the demand for general utility locomotive types was so pronounced that no good argument could be put forward for the introduction of a heavy locomotive dedicated to goods only. Another factor which acted against the project was the insufficient length of the receiving sidings in the yards, which made it doubtful that such a locomotive would have been able to be used to its full capacity.
Although the Class 22 was never built, the class number was not used for another steam locomotive type.
to the Eastern Transvaal and was scrapped in 1952 after only 15 years in service. Neither the Class 21 nor the aborted Class 22 design was subsequently repeated in either its original or modified form, leaving the impression that they represented advanced thinking that appears to have been considered as too far and too fast by Watson’s successors.
Steam locomotive
A steam locomotive is a railway locomotive that produces its power through a steam engine. These locomotives are fueled by burning some combustible material, usually coal, wood or oil, to produce steam in a boiler, which drives the steam engine...
with a Texas wheel arrangement in service, designed as a mixed traffic locomotive suitable for light rail. A simultaneously proposed heavier main line version Class 22 never materialised.
Manufacturer
The Class 21 2-10-4 steam locomotive was designed by A.G. Watson, Chief Mechanical Engineer (CME) of the South African Railways (SAR) from 1929 to 1936. It was built by the North British Locomotive CompanyNorth British Locomotive Company
The North British Locomotive Company was created in 1903 through the merger of three Glasgow locomotive manufacturing companies; Sharp Stewart and Company , Neilson, Reid and Company and Dübs and Company , creating the largest locomotive manufacturing company in Europe.Its main factories were...
(NBL) in Glasgow and delivered in 1937. Only the one locomotive was built, numbered 2551. At the time the design represented the maximum power obtainable from a ten-coupled non-articulated locomotive that was limited to a 15 long tons (15.2 t) axle load on 60 lb/yd rail.
Engine
Watson disliked articulated locomotives and his aim was to develop a powerful non articulated mixed traffic branch line locomotive with an axle load suitable for light rail. To enable it to negotiate tight curves, the third and fourth drivers were flangeless. It used a Watson Standard no. 3B boiler, the same as that used in the Class 15ESouth African Class 15E 4-8-2
Between 1935 and 1937 the South African Railways placed forty-four Class 15E steam locomotives with a 4-8-2 Mountain wheel arrangement in service. -Manufacturers:...
, Class 15F
South African Class 15F 4-8-2
The Class 15F was the most numerous steam locomotive class in South African Railways service. Between 1938 and 1946 two hundred and fifty-five of these steam locomotives with a 4-8-2 Mountain wheel arrangement were placed in service.-Manufacturers:...
and Class 23
South African Class 23 4-8-2
In 1938 and 1939 the South African Railways placed one hundred and thirty-six Class 23 steam locomotives in service. The Class 23 was the last and the largest 4-8-2 Mountain locomotive to be designed by the South African Railways.-Manufacturers:...
.
The end result could be considered as Watson’s answer to the Class GF 4-6-2+2-6-4
South African Class GF 4-6-2+2-6-4
In 1927 the South African Railways placed thirty-seven Class GF Garratt articulated steam locomotives with a 4-6-2+2-6-4 "Double Pacific" wheel arrangement in service. A further twenty-eight locomotives were delivered in 1928.-Manufacturers:...
Garratt locomotive, having very similar weight and tractive capacities. The Class 21 carried more water than the Garratt and was about 23 long tons (23.4 t) heavier with 43700 pound-forces (194.4 kN) tractive effort, compared to the 34200 pound-forces (152.1 kN) of the Class GF. Even so, only one Class 21 was produced and the design was not repeated.
Watson’s design called for cylinders with Rotary Cam Poppet valve gear, but since the locomotive was still under construction when Watson retired, his successor as CME, W.A.J. Day, made use of the opportunity to alter the specifications. Thus, in the year following Watson’s departure, the locomotive was delivered with Walschaerts valve gear.
Tender
The tender was an unusual experimental type using six pairs of wheels in a 2-8-22-8-2
Under the Whyte notation for the classification of steam locomotives, 2-8-2 represents the wheel arrangement of two leading wheels on one axle , eight powered and coupled driving wheels on four axles, and two trailing wheels on one axle...
wheel arrangement with the leading and trailing wheels in bissel type pony trucks and the rest of the axles mounted with a rigid wheelbase. The tender’s wheel arrangement did not prove to be very successful and, with the exception of a similar tender built in the Salt River shops for test purposes, was not used again.
The pony axle design is commonly used on steam locomotives with a single leading or trailing axle, and was also used on the Class 4E
South African Class 4E
Between 1952 and 1954 the South African Railways placed forty Class 4E electric locomotives with a 1Co+Co1 wheel arrangement in service.-Manufacturer:...
electric and Class 32-000
South African Class 32-000
Between November 1959 and November 1961 the South African Railways placed one hundred and fifteen Class 32-000 GE U18C1 diesel-electric locomotives in service in South West Africa.- Manufacturer :...
and 32-200
South African Class 32-200
In June and July 1966 the South African Railways placed ten Class 32-200 GE U20C1 diesel-electric locomotives in service in South West Africa..- Manufacturer :...
diesel-electric locomotives.
The aborted Class 22
A design for a Class 22 steam locomotive, Watson’s final design, was submitted at about the same time. The proposed Class 22 was also to have a 2-10-42-10-4
Under the Whyte notation for the classification of steam locomotives, a 2-10-4 locomotive has two leading wheels, ten driving wheels , and four trailing wheels...
Texas wheel arrangement, but was to be a heavy main line version of the Class 21, with an axle load of 22 long tons (22.4 t), the heaviest that current SAR track could bear on its 96 lb/yd rail. It was to have been a massive machine with larger 60 inches (1,524 mm) driving wheels, a larger 80 square feet (7.432 m²) grate and the larger Type EW tender that was later to be used with the Class 23
South African Class 23 4-8-2
In 1938 and 1939 the South African Railways placed one hundred and thirty-six Class 23 steam locomotives in service. The Class 23 was the last and the largest 4-8-2 Mountain locomotive to be designed by the South African Railways.-Manufacturers:...
locomotive.
If this locomotive had been built, it may have been one of the world’s most outstanding locomotives. The proposed boiler pressure was 250 pound per square inches (1,723.7 kPa), a figure never attained on the SAR, and its anticipated tractive effort of 66406 pound-forces (295.4 kN) at 75% of boiler pressure would have made it capable of handling loads of 2200 long tons (2,235 t) on the coal run from Witbank
Witbank
Witbank , also known as eMalahleni is a city situated on the Highveld of Mpumalanga, South Africa, within the eMalahleni Local Municipality. The name Witbank is Afrikaans for White Ridge and is named after a white sandstone outcrop where wagon transport drivers rested...
to Johannesburg
Johannesburg
Johannesburg also known as Jozi, Jo'burg or Egoli, is the largest city in South Africa, by population. Johannesburg is the provincial capital of Gauteng, the wealthiest province in South Africa, having the largest economy of any metropolitan region in Sub-Saharan Africa...
with comparative ease.
The design was a compromise between a 2-8-4 passenger class with 66 inches (1,676.4 mm) driving wheels and a 2-10-2 freight locomotive with 60 inches (1,524 mm) driving wheels. At the time, however, the demand for general utility locomotive types was so pronounced that no good argument could be put forward for the introduction of a heavy locomotive dedicated to goods only. Another factor which acted against the project was the insufficient length of the receiving sidings in the yards, which made it doubtful that such a locomotive would have been able to be used to its full capacity.
Although the Class 22 was never built, the class number was not used for another steam locomotive type.
Service
During its time in service, Class 21 number 2551 was equipped with smoke deflectors. It was mainly used on the line from PretoriaPretoria
Pretoria is a city located in the northern part of Gauteng Province, South Africa. It is one of the country's three capital cities, serving as the executive and de facto national capital; the others are Cape Town, the legislative capital, and Bloemfontein, the judicial capital.Pretoria is...
to the Eastern Transvaal and was scrapped in 1952 after only 15 years in service. Neither the Class 21 nor the aborted Class 22 design was subsequently repeated in either its original or modified form, leaving the impression that they represented advanced thinking that appears to have been considered as too far and too fast by Watson’s successors.
Gallery
The main picture shows number 2551 as delivered, without smoke deflectors.See also
- Tender locomotive numbering and classification
- Watson Standard boilers
- The 2-10-4 "Texas"
- List of South African locomotive classes