South African Class 16A 4-6-2

The South African Railways Class 16A 4-6-2 of 1915 was a steam locomotive.

South African Class 16A 4-6-2
Builder’s picture of no. 852
Type and origin Power type Steam Designer South African Railways (D.A. Hendrie) Builder North British Locomotive Company Serial number 20956-20957 Model Class 16A Build date 1915 Total produced 2
Specifications Configuration: ​  • Whyte 4-6-2 (Pacific)  • UIC 2'C1'h4 Driver 1st coupled axle (Inner cylinders) 2nd coupled axle (Outer cylinders) Gauge 3 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 wheels 34 in (864 mm) Wheelbase 57 ft 7+1⁄4 in (17,558 mm) ​  • Engine 31 ft 1 in (9,474 mm)  • Leading 6 ft 2 in (1,880 mm)  • Coupled 10 ft 9 in (3,277 mm)  • Tender 16 ft 9 in (5,105 mm)  • Tender bogie 4 ft 7 in (1,397 mm) Length: ​  • Over couplers 65 ft 11+5⁄8 in (20,107 mm) Height 12 ft 10 in (3,912 mm) Axle load 16 LT 18 cwt (17,170 kg) ​  • Leading 16 LT 8 cwt (16,660 kg)  • Coupled 16 LT 18 cwt (17,170 kg)  • Trailing 14 LT (14,220 kg)  • Tender bogie 27 LT 10 cwt (27,940 kg) Bogie 2: 23 LT 11 cwt (23,930 kg)  • Tender axle 13 LT 15 cwt (13,970 kg) Adhesive weight 50 LT 14 cwt (51,510 kg) Loco weight 81 LT 2 cwt (82,400 kg) Tender weight 51 LT 1 cwt (51,870 kg) Total weight 132 LT 3 cwt (134,300 kg) Tender type MP1 (2-axle bogies) MP, MP1, MR, MS, MT, MT1, MT2, MX, MY, MY1 permitted Fuel type Coal Fuel capacity 10 LT (10.2 t) Water cap. 4,250 imp gal (19,300 L) Firebox: ​  • Type Belpaire  • Grate area 36 sq ft (3.3 m2) Boiler: ​  • Pitch 7 ft 9 in (2,362 mm)  • Diameter 5 ft 1+5⁄8 in (1,565 mm)  • Tube plates 19 ft 9 in (6,020 mm)  • Small tubes 119: 2+1⁄4 in (57 mm)  • Large tubes 21: 5+1⁄2 in (140 mm) Boiler pressure 200 psi (1,379 kPa) Safety valve Ramsbottom Heating surface: ​  • Firebox 146 sq ft (13.6 m2)  • Tubes 1,975.5 sq ft (183.53 m2)  • Total surface 2,121.5 sq ft (197.09 m2) Superheater: ​  • Heating area 459.5 sq ft (42.69 m2) Cylinders Four Cylinder size 14 in (356 mm) bore 26 in (660 mm) stroke Valve gear Walschaerts Valve type Piston Couplers Johnston link-and-pin AAR knuckle (1930s)
Performance figures Tractive effort 25,480 lbf (113.3 kN) @ 75%
Career Operators South African Railways Class Class 16A Number in class 2 Numbers 851-852 Delivered 1915 First run 1915 Withdrawn 1944
The 2nd coupled axle had flangeless wheels

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.

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 (NBL) in Glasgow, Scotland. 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 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.

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 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.

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.

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 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

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  No. 852 on train no. 75 departing Braamfontein in June 1936