South African Class MJ1 2-6-6-0

In 1918 the South African Railways placed eight Class MJ1 Mallet articulated compound steam locomotives with a 2-6-6-0 wheel arrangement in branch line service.^[1][2][3]

Manufacturer

Because of the difficulties experienced by the usual British and German suppliers to build new locomotives during World War I, orders for the Class MJ1 2-6-6-0 Mallet articulated compound steam locomotive were placed with Montreal Locomotive Works (MLW) in Canada. The locomotive was designed by MLW, based on the specifications for the Class MJ Mallet that was designed by D.A. Hendrie, the Chief Mechanical Engineer (CME) of the South African Railways (SAR) from 1910 to 1922. Eight of these branch line locomotives were built and delivered by MLW in November 1918, numbered 1666 to 1673.^[1][3]

They were superheated, had Walschaerts valve gear and, like the Class MJ Mallets, had Belpaire fireboxes but slightly larger boilers. When compared to the Class MJ, a distinguishing feature of the Class MJ1 was the sandbox mounted on the boiler in North American style. In general appearance they were similar to the Class 14C and Class 15B 4-8-2 locomotives that were also built by MLW in 1918.^[1][3]

The Class MJ1 was the last Mallet locomotive class to be placed in service by the SAR and all its subsequent new articulated locomotives were to be Modified Fairlies and Garratts.^[4]

Compound expansion

In a compound locomotive steam is expanded in phases. After being expanded in a high pressure cylinder and having then lost pressure and given up part of its heat, it is exhausted into a larger volume low pressure cylinder for secondary expansion, after which it is exhausted through the smokebox. By comparison, in the more usual arrangement of simple expansion, steam is expanded just once in any one cylinder before being exhausted through the smokebox.^[1][5]

In the compound Mallet locomotive, the rear set of coupled wheels are driven by the smaller high pressure cylinders which are fed steam from the steam dome. Their spent steam is then fed to the larger low pressure cylinders that drive the front set of coupled wheels.^[1][3]

Service

The Class MJ1 was also intended for branch line working and joined the Class MJ Mallets in service in the Eastern Cape. All eight were still in service by March 1948, but they were all withdrawn from service by 1960.^[1][3][4]

See also

• Mallet locomotive
• South African Class MA 2-6-6-0
• South African Class MB 2-6-6-0
• South African Class MC 2-6-6-0
• South African Class MC1 2-6-6-0
• South African Class MD 2-6-6-2
• South African Class ME 2-6-6-2
• South African Class MF 2-6-6-2
• South African Class MG 2-6-6-2
• South African Class MH 2-6-6-2
• South African Class MJ 2-6-6-0
• Articulated locomotive numbering and classification
• The 2-6-6-0 Mallet
• List of South African locomotive classes

References

1. ^ ^{a b c d e f g h i} Holland, D.F. (1972). Steam Locomotives of the South African Railways, Volume 2: 1910-1955 (1st ed.). Newton Abbott, Devon: David & Charles. pp. 36-37. ISBN 0715354272. 
2. ^ ^{a b c d} South African Railways and Harbours Locomotive Diagram Book, 2’0” & 3’6” Gauge Steam Locomotives, 15 August 1941, as amended
3. ^ ^{a b c d e f} Paxton, Leith; Bourne, David (1985). Locomotives of the South African Railways (1st ed.). Cape Town: Struik. p. 88. ISBN 0869772112. 
4. ^ ^{a b} Durrant, A E (1989). Twilight of South African Steam (1st ed.). Newton Abbott, London: David & Charles. pp. 24-25. ISBN 0715386387. 
5. ^ Compounding Steam Engines