In 1915 the South African Railways placed two Class 16A four-cylinder simple steam locomotives with a 4-6-2

4-6-2

4-6-2, in the Whyte notation for the classification of steam locomotives, represents the wheel arrangement of four leading wheels on two axles , six powered and coupled driving wheels on three axles, and two trailing wheels on one axle .These locomotives are also known as Pacifics...

 Pacific wheel arrangement in passenger train service.

Manufacturer

The Class 16A 4-6-2 Pacific locomotive was designed by D.A. Hendrie, Chief Mechanical Engineer (CME) of the South African Railways (SAR) from 1910 to 1922, and was built in 1915 by the North British Locomotive Company

North British Locomotive Company

The North British Locomotive Company was created in 1903 through the merger of three Glasgow locomotive manufacturing companies; Sharp Stewart and Company , Neilson, Reid and Company and Dübs and Company , creating the largest locomotive manufacturing company in Europe.Its main factories were...

 (NBL) in Glasgow

Glasgow

Glasgow is the largest city in Scotland and third most populous in the United Kingdom. The city is situated on the River Clyde in the country's west central lowlands...

, Scotland

Scotland

Scotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the...

. Two locomotives were delivered, numbered 851 and 852. Also superheated and with Walschaerts valve gear and Belpaire firebox

Belpaire firebox

The Belpaire firebox is a type of firebox used on steam locomotives. It was invented by Alfred Belpaire of Belgium. It has a greater surface area at the top of the firebox, improving heat transfer and steam production...

es, they were identical in most respects to their predecessor, the Class 16

South African Class 16 4-6-2

In 1914 the South African Railways placed twelve Class 16 steam locomotives with a 4-6-2 Pacific wheel arrangement in passenger train service.-Manufacturer:The Class 16 4-6-2 Pacific locomotive was designed by D.A...

 that was delivered by NBL a year earlier, except that they had four cylinders instead of the usual two.

Four-cylinder experiment

With the Class 16A the SAR experimented with four-cylinder simple steam power. All four cylinders were arranged in line below the smokebox. The locomotive used Walschaerts valve gear with rocker arms attached to the tail ends of the outer piston valves, which then operated the adjacent inner piston’s valves. It operated in the so-called simple configuration whereby steam is fed directly to all four cylinders and used steam is exhausted directly through the smokebox and up the chimney by all cylinders.

All four cylinders were the same size with a 14 inches (355.6 mm) bore and 26 inches (660.4 mm) stroke, which presented a number of problems that had to be overcome to arrange two of these in the limited space between the frames. The outer cylinders drove the centre driving wheels while the inner cylinders operated on a cranked leading driving wheel axle, with each inside crank arranged at an angle of 180 degrees with its adjacent outside crank.

The arrangement made for a very smooth running locomotive capable of very fast running, since the shouldering effect that occurs on two-cylinder locomotives was completely absent. They were very popular with their crews because of their smooth and steady running.

They did, however, have less tractive effort than the two-cylinder Class 16. Even though the Class 16A experiment was successful, the available space on a 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 :...

 locomotive prevented larger cylinders from being fitted, and the four-cylinder design was therefore never repeated by the SAR.

Service

The two locomotives were placed in service on the Reef, where they operated with reasonable success. Their biggest disadvantage was the difficult access to the inner cylinders. They were withdrawn by 1945.

Gallery

The main picture shows number 852 on train Number 75, departing Braamfontein in June 1936.

See also

• South African Class 16 4-6-2
  South African Class 16 4-6-2
  In 1914 the South African Railways placed twelve Class 16 steam locomotives with a 4-6-2 Pacific wheel arrangement in passenger train service.-Manufacturer:The Class 16 4-6-2 Pacific locomotive was designed by D.A...
  
  
• South African Class 16B 4-6-2
  South African Class 16B 4-6-2
  In November 1917 the South African Railways placed ten Class 16B steam locomotives with a 4-6-2 Pacific wheel arrangement in passenger train service.-Manufacturer:The Class 16B 4-6-2 Pacific locomotive was designed by D.A...
  
  
• South African Class 16C 4-6-2
  South African Class 16C 4-6-2
  During 1919 the South African Railways placed ten Class 16C steam locomotives with a 4-6-2 Pacific wheel arrangement in passenger train service. Another twenty were placed in service in 1922.-Manufacturer:...
  
  
• South African Class 16D 4-6-2
  South African Class 16D 4-6-2
  In 1925 the South African Railways placed two Class 16D locomotives with a 4-6-2 Pacific wheel arrangement in passenger train service. Five more were placed in service in 1926.-Manufacturer:...
  
  
• South African Class 16DA 4-6-2
  South African Class 16DA 4-6-2
  In 1928 the South African Railways placed six Class 16DA steam locomotives with a 4-6-2 Pacific wheel arrangement in passenger train service. Eight more were placed in service in 1929, and another six in 1930.-Manufacturers:...
  
  
• South African Class 16E 4-6-2
  South African Class 16E 4-6-2
  In 1935 the South African Railways placed six Class 16E steam locomotives with a Pacific wheel arrangement in passenger train service.-Manufacturer:...
  
  
• Tender locomotive numbering and classification
• The 4-6-2 "Pacific"
• List of South African locomotive classes