South African Class 16A 4-6-2

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South African Class 16A 4-6-2
SAR Class 16A 852 (4-6-2).jpg
Builder’s picture of no. 852
Type and origin
Power typeSteam
DesignerSouth African Railways
(D.A. Hendrie)
BuilderNorth British Locomotive Company
Serial number20956-20957
ModelClass 16A
Build date1915
Total produced2
 • Whyte4-6-2 (Pacific)
 • UIC2'C1'h4
Driver1st coupled axle (Inner cylinders)
2nd coupled axle (Outer cylinders)
Gauge3 ft 6 in (1,067 mm) Cape gauge
Leading dia.30 in (762 mm)
Coupled dia.60 in (1,524 mm)
Trailing dia.33 in (838 mm)
Tender wheels34 in (864 mm)
Wheelbase57 ft 7 14 in (17,558 mm)
 • Engine31 ft 1 in (9,474 mm)
 • Leading6 ft 2 in (1,880 mm)
 • Coupled10 ft 9 in (3,277 mm)
 • Tender16 ft 9 in (5,105 mm)
 • Tender bogie4 ft 7 in (1,397 mm)
 • Over couplers65 ft 11 58 in (20,107 mm)
Height12 ft 10 in (3,912 mm)
Axle load16 LT 18 cwt (17,170 kg)
 • Leading16 LT 8 cwt (16,660 kg)
 • Coupled16 LT 18 cwt (17,170 kg)
 • Trailing14 LT (14,220 kg)
 • Tender bogie27 LT 10 cwt (27,940 kg)
Bogie 2: 23 LT 11 cwt (23,930 kg)
 • Tender axle13 LT 15 cwt (13,970 kg)
Adhesive weight50 LT 14 cwt (51,510 kg)
Loco weight81 LT 2 cwt (82,400 kg)
Tender weight51 LT 1 cwt (51,870 kg)
Total weight132 LT 3 cwt (134,300 kg)
Tender typeMP1 (2-axle bogies)
MP, MP1, MR, MS, MT, MT1, MT2, MX, MY, MY1 permitted
Fuel typeCoal
Fuel capacity10 LT (10.2 t)
Water cap4,250 imp gal (19,300 l)
Firebox typeBelpaire
 • Firegrate area36 sq ft (3.3 m2)
 • Pitch7 ft 9 in (2,362 mm)
 • Diameter5 ft 1 58 in (1,565 mm)
 • Tube plates19 ft 9 in (6,020 mm)
 • Small tubes119: 2 14 in (57 mm)
 • Large tubes21: 5 12 in (140 mm)
Boiler pressure200 psi (1,379 kPa)
Safety valveRamsbottom
Heating surface2,121.5 sq ft (197.09 m2)
 • Tubes1,975.5 sq ft (183.53 m2)
 • Firebox146 sq ft (13.6 m2)
 • Heating area459.5 sq ft (42.69 m2)
Cylinder size14 in (356 mm) bore
26 in (660 mm) stroke
Valve gearWalschaerts
Valve typePiston
CouplersJohnston link-and-pin
AAR knuckle (1930s)
Performance figures
Tractive effort25,480 lbf (113.3 kN) @ 75%
OperatorsSouth African Railways
ClassClass 16A
Number in class2
First run1915
The 2nd coupled axle had flangeless wheels

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 Pacific type wheel arrangement in passenger train service. They were designated Class 16A.[1][2][3]


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 (NBL) in Glasgow, Scotland. Two locomotives were delivered in November 1915, numbered 851 and 852.[2][3]

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 and Belpaire fireboxes, and were also delivered with Type MP1 tenders with a 10 long tons (10.2 tonnes) coal capacity and a 4,250 imperial gallons (19,300 litres) water capacity.[2][3][4][5][6]

Four-cylinder experiment[edit]

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 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.[2][3]

D.A. Hendrie

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 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.[1][2]

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.[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 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.[2][7]


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.[2][3]



  1. ^ a b c Holland, D. F. (1972). Steam Locomotives of the South African Railways. 2: 1910-1955 (1st ed.). Newton Abbott, Devon: David & Charles. p. 30. ISBN 978-0-7153-5427-8.
  2. ^ a b c d e f g 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.
  3. ^ a b c d e Paxton, Leith; Bourne, David (1985). Locomotives of the South African Railways (1st ed.). Cape Town: Struik. pp. 10–11, 65–66. ISBN 0869772112.
  4. ^ North British Locomotive Company works list, compiled by Austrian locomotive historian Bernhard Schmeiser
  5. ^ South 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.
  6. ^ 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.
  7. ^ Durrant, A. E. (1989). Twilight of South African Steam (1st ed.). Newton Abbott, London: David & Charles. pp. 17–18. ISBN 0715386387.