South African Class MF 2-6-6-2

The South African Class MF 2-6-6-2 of 1911 is a South African steam locomotive from the pre-Union era in the Transvaal.

In 1911 the Central South African Railways placed nine Mallet articulated compound steam locomotives with a 2-6-6-2 wheel arrangement in service. In 1912, when they were assimilated into the South African Railways, they were renumbered and classified as Class MF. Five more of these locomotives were delivered in November 1911 and were numbered directly onto the South African Railways roster.^[1][2][3]

Manufacturer

The nine Mallet articulated compound steam locomotives that were delivered to the Central South African Railways (CSAR) in 1911 were built by the American Locomotive Company (ALCO) in 1910 and 1911. They were very similar to the experimental Class MD that was delivered in 1910, but they were equipped with Schmidt superheaters. They had Walschaerts valve gear and were numbered in the range from 1015 to 1023.^[1][2][3][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][2]

South African Railways

The Union of South Africa was established on 31 May 1910, in terms of the South Africa Act, enacted by the Parliament of the United Kingdom. One of the clauses in the Act required that the three Colonial Government railways, the Cape Government Railways, the Natal Government Railways and the CSAR, also be united under one single administration to control and administer the railways, ports and harbours of the Union. While the South African Railways (SAR) came into existence in 1910, the actual classification and renumbering of all the rolling stock of the three constituent railways required careful planning and was only implemented with effect from 1 January 1912.^[3][6]

In 1912 these locomotives were renumbered in the range from 1619 to 1627 and classified as Class MF on the SAR. Five more of the type were delivered from ALCO in November 1911, but these were numbered in the range from 1629 to 1633, directly onto the SAR roster.^[1][2][3]

Service

The Class MF joined the experimental Class MD on the coal traffic line between Witbank and Germiston. They were acquired to improve the traffic flow on this line with its ruling gradient of one in one hundred, where the increase of traffic and the resultant congestion was causing considerable delays en route that led to excessive hours of duty being imposed on crews. When they replaced the existing Class 11 locomotives on this line, train loads could be increased from 900 long tons (914 tonnes) to 1,600 long tons (1,626 tonnes).^[1][2]

The Mallets proved to be capable of handling the heavy coal loads. In May 1914 Class MF number 1620 was used in a test run from Witbank to Germiston, hauling fifty-five bogie wagons with an all-up weight of 1,626 long tons (1,652 tonnes). The 80 miles (129 kilometres) journey was accomplished in seven hours, which included several stops.^[1]

Modification

In 1923 engine number 1620 was converted to a simple expansion (simplex) locomotive in the Salvokop shops in Pretoria. Five more, numbers 1621 to 1623, 1631 and 1632, were also converted to simplex locomotives in 1925. Three of these, numbers 1620, 1631 and 1632, were then transferred to East London where more powerful locomotives were needed since the line had a heavy gradient of one in forty that started right at the end of the departing platform, making it an extremely difficult section. They appear to have not been up to the task in the Eastern Cape, however, since by 1926 they were observed there, staged out of service.^[1][2]

They were all withdrawn from service by 1939.^[2]

See also

• Articulated locomotive numbering and classification
• List of South African locomotive classes
• Mallet locomotive
• South African Class MD 2-6-6-2
• South African Class ME 2-6-6-2
• South African Class MG 2-6-6-2
• South African Class MH 2-6-6-2
• South African locomotive history
• The 2-6-6-2 Mallet

References

Wikimedia Commons has media related to: South African Class MF (2-6-6-2)

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