The South African Railways Class 16A 4-6-2 of 1915 was a steam locomotive. In 1915, the South African Railways placed two experimental four-cylinder simple expansion steam locomotives with a

4-6-2 Under 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. The locomotiv ...

Pacific type wheel arrangement in passenger train service. They were designated Class 16A.Espitalier, T.J.; Day, W.A.J. (1945). ''The Locomotive in South Africa - A Brief History of Railway Development. Chapter VII - South African Railways (Continued).'' South African Railways and Harbours Magazine, August 1945. pp. 594-595.

Manufacturer

The Class 16A 4-6-2 Pacific type 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 The North British Locomotive Company (NBL, NB Loco or North British) was created in 1903 through the merger of three Glasgow locomotive manufacturing companies; Sharp, Stewart and Company (Atlas Works), Neilson, Reid and Company (Hyde Park Wor ...

(NBL) in

Glasgow Glasgow ( ; sco, Glesca or ; gd, Glaschu ) is the most populous city in Scotland and the fourth-most populous city in the United Kingdom, as well as being the 27th largest city by population in Europe. In 2020, it had an estimated popul ...

Scotland Scotland (, ) is a country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a border with England to the southeast and is otherwise surrounded by the Atlantic Ocean to the ...

. Two locomotives were delivered in November 1915, numbered 851 and 852. Except that they had four cylinders instead of the usual two, they were identical in most respects to their predecessors, the Class 16, which were delivered by NBL a year earlier. They were also superheated, with

Walschaerts valve gear The Walschaerts valve gear is a type of valve gear used to regulate the flow of steam to the pistons in steam locomotives, invented by Belgium, Belgian railway mechanical engineering, engineer Egide Walschaerts in 1844. The gear is sometimes name ...

and

Belpaire firebox The Belpaire firebox is a type of firebox used on steam locomotives. It was invented by Alfred Belpaire of Belgium in 1864. Today it generally refers to the shape of the outer shell of the firebox which is approximately flat at the top and squa ...

es, and were also delivered with Type MP1 tenders with a coal capacity and a water capacity.North British Locomotive Company works list, compiled by Austrian locomotive historian Bernhard SchmeiserSouth African Railways & Harbours/Suid Afrikaanse Spoorweë en Hawens (15 Aug 1941). ''Locomotive Diagram Book/Lokomotiefdiagramboek, 3'6" Gauge/Spoorwydte''. SAR/SAS Mechanical Department/Werktuigkundige Dept. Drawing Office/Tekenkantoor, Pretoria. p. 43.South African Railways & Harbours/Suid Afrikaanse Spoorweë en Hawens (15 Aug 1941). ''Locomotive Diagram Book/Lokomotiefdiagramboek, 2'0" & 3'6" Gauge/Spoorwydte, Steam Locomotives/Stoomlokomotiewe''. SAR/SAS Mechanical Department/Werktuigkundige Dept. Drawing Office/Tekenkantoor, Pretoria. pp. 6a-7a, 41, 43.

Four-cylinder experiment

With the Class 16A, Hendrie experimented with four-cylinder simple expansion (simplex) steam power. All four cylinders were arranged in line below the smokebox. The Walschaerts valve gear had rocker arms attached to the tail ends of the outer piston valves which passed through the frames and then actuated the adjacent inner piston's valves. It operated in the

simplex In geometry, a simplex (plural: simplexes or simplices) is a generalization of the notion of a triangle or tetrahedron to arbitrary dimensions. The simplex is so-named because it represents the simplest possible polytope in any given dimension. ...

configuration, whereby steam is fed directly to all four cylinders and spent steam is exhausted by all cylinders directly through the smokebox and up the chimney.

All four cylinders were the same size, with a bore and stroke, which presented a number of problems which had to be overcome to arrange two of these in the limited space between the frames. The outer cylinders drove the centre pair of coupled wheels, while the inner cylinders operated on a cranked leading coupled wheel axle. Each inside crank was 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 which 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 A cape is a clothing accessory or a sleeveless outer garment which drapes the wearer's back, arms, and chest, and connects at the neck. History Capes were common in medieval Europe, especially when combined with a hood in the chaperon. Th ...

locomotive for four equal-sized in-line cylinders would prevent larger diameter 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. The last of these locomotives was withdrawn from service and scrapped during 1944.

Illustration

File:SAR Class 16A 852 (4-6-2) a.jpg, No. 852 on train no. 75 departing

Braamfontein Braamfontein (English: ''blackberry spring'', or more prosaicly ''blackberry springs''; also known as Braam) is a central suburb of Johannesburg, in South Africa, seat of the Constitutional Court of South Africa and some of South Africa's major c ...

in June 1936

References

{{Steam locomotive tenders

1890 Events January–March * January 1 ** The Kingdom of Italy establishes Eritrea as its colony, in the Horn of Africa. ** In Michigan, the wooden steamer ''Mackinaw'' burns in a fire on the Black River. * January 2 ** The steamship ...

4-6-2 locomotives 2′C1′ h4 locomotives NBL locomotives Cape gauge railway locomotives Railway locomotives introduced in 1915 1915 in South Africa Scrapped locomotives