South African Class MD 2-6-6-2
Encyclopedia
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. In 1912, when it was assimilated into the South African Railways, it was renumbered and classified as Class MD.
in 1910. It was numbered 1001 and placed in service in March 1910, and with its full working order weight of 157 long tons (160 t) it was the heaviest locomotive in the world working on Cape gauge
at the time. It had Walschaerts valve gear and used saturated steam.
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.
locomotives on this line with more powerful Mallets, in order to be able to increase train loads from 900 long tons (914 t) to 1600 long tons (1,626 t).
In 1912, when the locomotive was taken onto the South African Railways (SAR) roster, it was renumbered 1617 and classified as the sole Class MD. It remained in service on the line between Witbank and Germiston until it was withdrawn from service and scrapped in 1926.
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...
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 it was assimilated into the South African Railways, it was renumbered and classified as Class MD.
Manufacturer
The first Mallet articulated compound steam locomotive on the Central South African Railways (CSAR) was ordered for test purposes from the American Locomotive CompanyAmerican Locomotive Company
The American Locomotive Company, often shortened to ALCO or Alco , was a builder of railroad locomotives in the United States.-Early history:...
in 1910. It was numbered 1001 and placed in service in March 1910, and with its full working order weight of 157 long tons (160 t) it was the heaviest locomotive in the world working on Cape gauge
Cape gauge
Cape gauge is a track gauge of between the inside of the rail heads and is classified as narrow gauge. It has installations of around .The gauge was first used by Norwegian engineer Carl Abraham Pihl and the first line was opened in 1862.- Nomenclature :...
at the time. It had Walschaerts valve gear and used saturated steam.
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.
Performance
At low speed the locomotive proved to be capable of handling heavier trains than any of the existing CSAR fleet of goods locomotives, but at higher speeds of 25 to 30 mph (40.2 to 48.3 km/h) it could not compete successfully because of excessive wear on the moving parts that resulted in failures and, as a consequence, high maintenance cost. It has been surmised that, had it been superheated and equipped with larger diameter driving wheels, the results may have been much better.Service
The Mallet was acquired as an experiment, the ultimate object being to improve traffic flow on the 80 miles (129 km) coal line between Witbank and Germiston. The increase of traffic and the resultant congestion on this line with its ruling gradient of one in one hundred was causing considerable delays en route that led to excessive hours of duty being imposed on crews. The intent was to determine the feasibility of replacing the existing Class 11South 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 with more powerful Mallets, in order to be able to increase train loads from 900 long tons (914 t) to 1600 long tons (1,626 t).
In 1912, when the locomotive was taken onto the South African Railways (SAR) roster, it was renumbered 1617 and classified as the sole Class MD. It remained in service on the line between Witbank and Germiston until it was withdrawn from service and scrapped in 1926.
See also
- Mallet locomotiveMallet locomotiveThe Mallet Locomotive is a type of articulated locomotive, invented by a Swiss engineer named Anatole Mallet ....
- South African Class MA 2-6-6-0South African Class MA 2-6-6-0In 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.-Manufacturer:...
- South African Class MB 2-6-6-0South African Class MB 2-6-6-0In 1910 the Natal Government Railways placed five 2-6-6-0 Mallet articulated compound steam locomotives in service. In 1912, when they were assimilated into the South African Railways, they were renumbered and classified as Class MB.-Manufacturer:...
- South African Class MC 2-6-6-0South African Class MC 2-6-6-0In 1912 the South African Railways placed ten Class MC Mallet articulated compound steam locomotives with a 2-6-6-0 wheel arrangement in service.-Manufacturer:...
- South African Class MC1 2-6-6-0South African Class MC1 2-6-6-0In 1914 the South African Railways placed fifteen Class MC1 Mallet articulated compound steam locomotives with a 2-6-6-0 wheel arrangement in service.-Manufacturer:...
- South African Class ME 2-6-6-2South African Class ME 2-6-6-2In January 1912 the South African Railways placed a single Class ME Mallet articulated steam locomotive with a 2-6-6-2 wheel arrangement in service.-Manufacturer:...
- South African Class MF 2-6-6-2South African Class MF 2-6-6-2In 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...
- South African Class MG 2-6-6-2South African Class MG 2-6-6-2In 1911 the Central South African Railways placed a single experimental Mallet articulated compound steam locomotive with a 2-6-6-2 wheel arrangement in service...
- South African Class MH 2-6-6-2South African Class MH 2-6-6-2In 1915 the South African Railways placed five Class MH Mallet articulated compound steam locomotives with a 2-6-6-2 wheel arrangement in service.-Manufacturer:...
- South African Class MJ 2-6-6-0South African Class MJ 2-6-6-0Between 1914 and 1921 the South African Railways placed eighteen Class MJ Mallet articulated compound steam locomotives with a 2-6-6-0 wheel arrangement in branch line service.-Manufacturers:...
- South African Class MJ1 2-6-6-0South African Class MJ1 2-6-6-0In 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.-Manufacturer:...
- Articulated locomotive numbering and classification
- The 2-6-6-2 Mallet2-6-6-2In 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...
- List of South African locomotive classes