South African Class MF 2-6-6-2 - AbsoluteAstronomy.com

In 1911 the Central South African Railways placed nine Mallet articulated compound steam locomotive

Compound locomotive

A compound engine unit is a type of steam engine where steam is expanded in two or more stages.A typical arrangement for a compound engine is that the steam is first expanded in a high-pressure cylinder, then having given up heat and losing pressure, it exhausts directly into one or more larger...

s with a 2-6-6-2

2-6-6-2

In Whyte notation, 2-6-6-2 refers to a railroad steam locomotive that has two leading wheels followed by six coupled driving wheels, a second set of six coupled driving wheels, and two trailing wheels...

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.

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

American Locomotive Company

The American Locomotive Company, often shortened to ALCO or Alco , was a builder of railroad locomotives in the United States.-Early history:...

(ALCO) between 1910 and 1911. They were very similar to the experimental Class MD that was delivered in 1910, but they were equipped with Schmidt

Wilhelm Schmidt (engineer)

Wilhelm Schmidt, known as Hot Steam Schmidt was a German engineer and inventor who achieved the breakthrough in the development of superheated steam technology for steam engines....

superheaters. They had Walschaerts valve gear and were numbered 1015 to 1023.

In 1912, when these locomotives were taken onto the South African Railways (SAR) roster, they were renumbered 1619 to 1627 and classified as Class MF. Five more of the type were delivered from ALCO in November 1911, but these were numbered 1629 to 1633 directly onto the SAR roster.

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.

In the compound Mallet locomotive

Mallet locomotive

The Mallet Locomotive is a type of articulated locomotive, invented by a Swiss engineer named Anatole Mallet ....

, 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.

Service

The Class MF joined the experimental Class MD

South African Class MD 2-6-6-2

In March 1910 the Central South African Railways placed a single experimental Mallet articulated compound steam locomotive with a 2-6-6-2 wheel arrangement in service...

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

South African Class 11 2-8-2

In 1904 the Central South African Railways placed thirty-six Class 11 steam locomotives with a 2-8-2 Mikado wheel arrangement in service. When these locomotives were assimilated into the South African Railways in 1912, they were renumbered but retained their Class 11...

locomotives on this line, train loads could be increased from 900 long tons (914 t) to 1600 long tons (1,626 t).

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 1626 long tons (1,652 t). The 80 miles (129 km) journey was accomplished in seven hours, which included several stops.

Modification

In 1923 engine number 1620 was converted to a simple expansion locomotive in the Koedoespoort 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.

They were all withdrawn from service by 1939.

Manufacturer

Compound expansion

Service

Modification

See also