South African Class 16DA 4-6-2 1930

South African Class 16DA 4-6-2 1930
No. 876 taking water at Thaba Nchu, 4 July 1999
Type and origin ♠ With 60 inch (1,524 mm) coupled wheels ♥ With 63 inch (1,600 mm) coupled wheels Power type Steam Designer South African Railways (A.G. Watson) Builder Henschel and Son Serial number 21749-21754 Model Class 16DA Build date 1930 Total produced 6
Specifications Configuration: ​  • Whyte 4-6-2 (Pacific)  • UIC 2'C1'h2 Driver 2nd coupled axle Gauge 3 ft 6 in (1,067 mm) Cape gauge Leading dia. 30 in (762 mm) Coupled dia. ♠ 60 in (1,524 mm) ♥ 63 in (1,600 mm) Trailing dia. 34 in (864 mm) Tender wheels 34 in (864 mm) Wheelbase 60 ft 3 1⁄4 in (18,371 mm)  • Engine 30 ft 8 in (9,347 mm)  • Leading 6 ft 10 in (2,083 mm)  • Coupled 11 ft (3,353 mm)  • Tender 20 ft 5 in (6,223 mm)  • Tender bogie 6 ft 2 in (1,880 mm) Length: ​  • Over couplers 68 ft 4 1⁄8 in (20,831 mm) Height ♠ 12 ft 10 in (3,912 mm) ♥ 12 ft 11 1⁄2 in (3,950 mm) Frame type Bar Axle load ♠ 19 LT 10 cwt (19,810 kg) ♥ 19 LT 15 cwt 1 qtr (20,080 kg)  • Leading ♠♥ 17 LT 7 cwt (17,630 kg)  • 1st coupled ♠ 19 LT 10 cwt (19,810 kg) ♥ 19 LT 15 cwt 1 qtr (20,080 kg)  • 2nd coupled ♠ 19 LT 7 cwt 3 qtr (19,700 kg) ♥ 19 LT 13 cwt (19,970 kg)  • 3rd coupled ♠ 19 LT 2 cwt (19,410 kg) ♥ 19 LT 7 cwt 1 qtr (19,670 kg)  • Trailing ♠♥ 15 LT 18 cwt (16,160 kg)  • Tender bogie Bogie 1: 33 LT 18 cwt (34,440 kg) Bogie 2: 35 LT 10 cwt (36,070 kg)  • Tender axle 17 LT 15 cwt (18,030 kg) Adhesive weight ♠ 57 LT 19 cwt 3 qtr (58,920 kg) ♥ 58 LT 15 cwt 2 qtr (59,720 kg) Loco weight ♠ 91 LT 4 cwt 3 qtr (92,700 kg) ♥ 92 LT 0 cwt 2 qtr (93,500 kg) Tender weight 69 LT 8 cwt (70,510 kg) Total weight ♠ 160 LT 12 cwt 3 qtr (163,200 kg) ♥ 161 LT (163.58355232 t) Tender type KT (2-axle bogies) Fuel type Coal Fuel capacity 14 LT (14.2 t) Water cap 6,000 imp gal (27,300 l) Firebox type Round-top  • Firegrate area 60 sq ft (5.6 m2) Boiler: ​  • Pitch ♠ 8 ft 6 in (2,591 mm) ♥ 8 ft 7 1⁄2 in (2,629 mm)  • Diameter 5 ft 10 1⁄4 in (1,784 mm)  • Tube plates 17 ft 10 5⁄8 in (5,451 mm)  • Small tubes 142: 2 1⁄4 in (57 mm)  • Large tubes 34: 5 1⁄2 in (140 mm) Boiler pressure ♠ 195 psi (1,344 kPa) ♥ 205 psi (1,413 kPa) Safety valve Pop Heating surface 2,565 sq ft (238.3 m2)  • Tubes 2,371 sq ft (220.3 m2)  • Arch tubes 22 sq ft (2.0 m2)  • Firebox 172 sq ft (16.0 m2) Superheater: ​  • Heating area 620 sq ft (58 m2) Cylinders Two Cylinder size 23 in (584 mm) bore 26 in (660 mm) stroke Valve gear Walschaerts Caprotti (No. 879 as built) Valve type Piston Poppet (No. 879 as built) Couplers AAR knuckle
Performance figures Tractive effort ♠ 33,530 lbf (149.1 kN) @ 75% ♥ 33,570 lbf (149.3 kN) @ 75%
Career Operators South African Railways Class Class 16DA Number in class 6 Numbers 874-879 Nicknames Boepens, Wide firebox Delivered 1930 First run 1930 Withdrawn 1973

The South African Railways Class 16DA 4-6-2 of 1930 was a steam locomotive.

In 1930, the South African Railways placed six redesigned Class 16DA steam locomotives with a 4-6-2 Pacific type wheel arrangement in passenger train service.

An order for six locomotives for the South African Railways (SAR), similar to the Class 16DA Pacific type locomotives of 1928 and 1929 but built to an improved design, was placed with Henschel and Son of Kassel in Germany in 1930.

In an attempt to improve the steaming properties of further orders of Class 16DA locomotives, A.G. Watson, who had succeeded Colonel Collins as CME in 1929, designed a boiler of the Wootten type. It had a very wide firebox with a grate area of 60 square feet (5.574 square metres). Watson was a firm believer in large firegrates with enlarged blast pipe caps to give a reasonably low burning rate of fuel per unit of grate area, which improved boiler efficiency and reduced the emission of sparks and partially burnt fuel.

The boiler itself was of the same dimensions as that of the earlier locomotives in terms of girth and length between tube plates, the only difference being in the tube arrangement. The enlarged firebox, however, had a firegrate area which was 33⅓% larger than the 45 square feet (4.181 square metres) of the earlier Hohenzollern- and Baldwin-built locomotives. It was of comparable proportions to those which would later be installed on the Class 15E and Class 23.

This boiler and firebox was installed on these final six Class 16DA locomotives, numbered in the range from 874 to 879, which were built by Henschel and delivered in 1930. Compared to the earlier Hohenzollern- and Baldwin-built locomotives, the steaming ability of the six Henschel-built locomotives was phenomenal and led to the adoption of wide fireboxes without combustion chambers as the standard on all subsequent SAR mainline steam locomotives.

The Henschel-built Class 16DA locomotives with their much wider fireboxes, their correspondingly larger grate areas and slightly larger diameter trailing wheels were sufficiently different from the Baldwin- and Hohenzollern-builts to justify a separate classification such as Class 16DB, but this did not happen and the locomotives ended up being known as the Wide Firebox or Boepens Class 16DA.

Five of these locomotives were delivered with Walschaerts valve gear. The last engine, no. 879, was built with Caprotti valve gear for experimental purposes. This rotary poppet valve gear was driven from a single gearbox on the centre of the driving axle. The valve gear was given a fair trial, but was eventually replaced with the standard Walschaerts valve gear in 1940.