South African Class 16A 4-6-2

In 1915 the South African Railways placed two Class 16A four-cylinder simple steam locomotives with a 4-6-2 Pacific wheel arrangement in passenger train service.^[3]

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 (NBL) in Glasgow, Scotland. Two locomotives were delivered, numbered 851 and 852. Also superheated and with Walschaerts valve gear and Belpaire fireboxes, they were identical in most respects to their predecessor, the Class 16 that was delivered by NBL a year earlier, except that they had four cylinders instead of the usual two.^[3]

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.^[3]

All four cylinders were the same size with a 14 inches (356 millimetres) bore and 26 inches (660 millimetres) 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.^[1]

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.^[1]

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 locomotive prevented larger cylinders from being fitted, and the four-cylinder design was therefore never repeated by the SAR.^[4]

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.^[3]

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 16B 4-6-2
• South African Class 16C 4-6-2
• South African Class 16D 4-6-2
• South African Class 16DA 4-6-2
• South African Class 16E 4-6-2
• Tender locomotive numbering and classification
• The 4-6-2 "Pacific"
• List of South African locomotive classes

References

1. ^ ^{a b c d e} Holland, D.F. (1972). Steam Locomotives of the South African Railways, Volume 2: 1910-1955 (1st ed.). Newton Abbott, Devon: David & Charles. p. 30. ISBN 0715354272. 
2. ^ North British Locomotive Company works list, compiled by Austrian locomotive historian Bernhard Schmeiser
3. ^ ^{a b c d} Paxton, Leith; Bourne, David (1985). Locomotives of the South African Railways (1st ed.). Cape Town: Struik. pp. 10-11, 65-66. ISBN 0869772112. 
4. ^ Durrant, A E (1989). Twilight of South African Steam (1st ed.). Newton Abbott, London: David & Charles. pp. 17-18. ISBN 0715386387.