South African Class MA 2-6-6-0

In 1909 the Natal Government Railways placed a single 2-6-6-0 Mallet articulated compound steam locomotive in service. In 1912, when it was assimilated into the South African Railways, it was renumbered and classified as Class MA.^[1][2][4]

Manufacturer

As a result of a visit to the United States of America by Natal Government Railways (NGR) Locomotive Superintendent D.A. Hendrie in 1909 to study Mallet type locomotives and also American locomotive design in general, the American Locomotive Company (ALCO) supplied the NGR with two experimental locomotives that represented a radical departure from previous NGR locomotive designs. One was the Class American D, later to become the Class 3A on the South African Railways (SAR), while the other was the first Mallet type compound steam locomotive in South Africa.^[1][4]

Characteristics

The locomotive had Walschaerts valve gear, a bar frame and used saturated steam. It was the first acticulated compound steam locomotive to enter service in South Africa and its design and large proportions represented a big advance in motive power on Cape gauge. At the time it was the most powerful locomotive in the country.^[1][4]

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.^[1][5]

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, from which spent steam is then fed to the larger low pressure cylinders that drive the front set of coupled wheels.^[1][4]

While the results obtained with the Mallet in service were encouraging, it might have been better than adequate if the locomotive had been superheated. Even so, the locomotive’s performance was good enough to warrant subsequent orders for a further five slightly larger and more powerful compound Mallets.^[1][4]

Service

The locomotive was placed in service banking heavy coal trains between Estcourt and Highlands on the Natal main line. In 1912, when it was taken onto the SAR roster, it was renumbered 1601 and classified as the sole Class MA. It was withdrawn from service in 1927.^[1][2][4]

See also

• Mallet locomotive
• 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
• South African Class MJ1 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 j k} Holland, D.F. (1971). Steam Locomotives of the South African Railways, Volume 1: 1859-1910 (1st ed.). Newton Abbott, Devon: David & Charles. pp. 103-105. ISBN 0715353829. 
2. ^ ^{a b c} Classification of S.A.R. Engines with Renumbering Lists, issued by the Chief Mechanical Engineer’s Office, Pretoria, January 1912, pp. 9, 12, 15, 46 (Reprinted in April 1987 by SATS Museum, R.3125-6/9/11-1000)
3. ^ Holland, D.F. (1972). Steam Locomotives of the South African Railways, Volume 2: 1910-1955 (1st ed.). Newton Abbott, Devon: David & Charles. p. 140. ISBN 0715354272. 
4. ^ ^{a b c d e f} Paxton, Leith; Bourne, David (1985). Locomotives of the South African Railways (1st ed.). Cape Town: Struik. pp. 84-85. ISBN 0869772112. 
5. ^ ^{a b} Compounding Steam Engines