South African Class 21 2-10-4

Class 21 2-10-4 no. 2551 with smoke deflectors installed

Type and origin
Power type	Steam
Designer	South African Railways
Builder	North British Locomotive Company
Serial number	24379
Model	Class 21
Build date	1937
Total produced	1

Specifications
Configuration	2-10-4 "Texas"
Gauge	3 ft 6 in (1,067 mm) Cape gauge
Leading dia	30 in (762 mm)
Driver diameter	54 in (1,372 mm)
Trailing dia	30 in (762 mm)
Wheelbase	Engine: 18 ft 9 in (5,715 mm) coupled 4 ft 6 in (1,372 mm) trailing 36 ft 9 in (11,201 mm) total Tender: 12 ft 3 in (3,734 mm) rigid wheelset 22 ft 3 in (6,782 mm) total Total: 68 ft 4.0625 in (20,830 mm)
Length	76 ft 10.0625 in (23,420 mm)
Height	13 ft (3,962 mm)
Axle load	14.95 long tons (15.2 t) on 3rd driver
Adhesive weight	72.85 long tons (74.0 t)
Loco weight	106.6 long tons (108.3 t)
Tender weight	69,122 lb (31.4 t) empty 65.8 long tons (66.9 t) w/o
Loco & tender weight	206,916 lb (93.9 t) empty 172.4 long tons (175.2 t) w/o
Tender type	FT * 2-8-2 wheel arrangement * 34 in (864 mm) wheels * Length 32 ft 7.4375 in (9,943 mm)
Fuel type	Coal
Fuel capacity	10 long tons (10.2 t)
Water cap	5,587 imp gal (25,400 l)
Firebox: • Firegrate area	63 sq ft (5.853 m²)
Boiler	6 ft 2.25 in (1,886 mm) inside diameter 22 ft 6 in (6,858 mm) inside length 9 ft (2,743 mm) pitch
Boiler pressure	210 psi (1,450 kPa)
Heating surface	3,400 sq ft (315.870 m²)
• Tubes	136 tubes 2.5 in (64 mm) diameter 36 tubes 5.5 in (140 mm) diameter 3,168 sq ft (294.317 m²)
• Flues	26 sq ft (2.415 m²)
• Firebox	206 sq ft (19.138 m²)
Superheater: • Heating area	676 sq ft (62.802 m²)
Cylinders	Two
Cylinder size	24 in (610 mm) bore 26 in (660 mm) stroke
Valve gear	Walschaerts

Performance figures
Tractive effort	45,700 lbf (203 kN) at 75% pressure

Career
Operators	South African Railways
Class	Class 21
Number in class	1
Numbers	2551
Delivered	1937
First run	1937
Retired	1952

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The South African Railways Class 21 2-10-4 of 1937 is a steam locomotive.

In 1937 the South African Railways placed a single Class 21 steam locomotive with a 2-10-4 Texas type wheel arrangement in service, designed as a mixed traffic locomotive suitable for use on light rail. A simultaneously proposed heavier mainline version Class 22 2-10-4 never materialised.^[1]^[2]^[3]

Manufacturer

The Class 21 2-10-4 Texas type locomotive was designed by A.G. Watson, Chief Mechanical Engineer (CME) of the South African Railways (SAR) from 1929 to 1936. It was built by the North British Locomotive Company (NBL) in Glasgow and delivered in 1937. Only the one locomotive was built, numbered 2551. At the time the design represented the maximum power obtainable from a ten-coupled non-articulated locomotive that was limited to a 15 long tons (15.2 tonnes) axle load on 60 pounds per yard (30 kilograms per metre) rail.^[1]^[3]^[4]

Design

Engine

Watson disliked articulated locomotives and his aim was to develop a powerful non articulated mixed traffic branchline locomotive with an axle load suitable for light rail. To enable it to negotiate tight curves, the third and fourth coupled wheelsets were flangeless. It used a Watson Standard no. 3B boiler, the same as that used in the Class 15E, Class 15F and Class 23.^[1]^[3]

The end result could be considered as Watson’s answer to the Class GF 4-6-2+2-6-4 Garratt locomotive, having very similar axle loads. The Class 21 carried more water than the Garratt and was about 23 long tons (23.4 tonnes) heavier with 43,700 pounds-force (194.4 kilonewtons) tractive effort, compared to the 34,200 pounds-force (152.1 kilonewtons) of the Class GF. Even so, only one Class 21 was produced and the design was not repeated.^[1]^[3]^[5]

Watson’s design called for cylinders with Rotary Cam Poppet valve gear, but since the locomotive was still under construction when Watson retired, his successor as CME, W.A.J. Day, made use of the opportunity to alter the specifications. Thus, in the year following Watson’s departure, the Class 21 locomotive was delivered with Walschaerts valve gear.^[1]^[3]^[5]

Tender

The tender was an unusual experimental type using six pairs of wheels in a 2-8-2 wheel arrangement with the leading and trailing wheels in bissel type pony trucks and the rest of the axles mounted with a rigid wheelbase. The tender’s wheel arrangement did not prove to be very successful and, with the exception of a similar tender built in the Salt River shops for test purposes, was not used again on the SAR.^[1]^[3]

The pony axle design is commonly used on steam locomotives with a single leading or trailing axle, and was also used on the Class 4E electric and Class 32-000 and 32-200 diesel-electric locomotives.^[3]

The aborted Class 22

A design for a Class 22 steam locomotive, Watson’s final design, was submitted at about the same time. The proposed Class 22 was also to have a 2-10-4 Texas wheel arrangement, but was to be a heavy mainline version of the Class 21, with an axle load of 22 long tons (22.4 tonnes), the heaviest that current SAR track could bear on its 96 pounds per yard (48 kilograms per metre) mainline rail. It was to have been a massive machine with larger 60 inches (1,524 millimetres) coupled wheels, a larger 80 square feet (7.432 square metres) grate and the larger Type EW tender that was later to be used with the Class 23 locomotive.^[1]^[3]^[5]

If this locomotive had been built, it may have been one of the world’s most outstanding locomotives. The proposed boiler pressure was 250 pounds per square inch (1,720 kilopascals), a figure never attained on the SAR, and its anticipated tractive effort of 66,406 pounds-force (295.4 kilonewtons) at 75% of boiler pressure would have made it capable of handling loads of 2,200 long tons (2,235 tonnes) on the coal run from Witbank to Johannesburg with comparative ease.^[1]^[5]

The design was a compromise between a 2-8-4 passenger class with 66 inches (1,676 millimetres) coupled wheels and a 2-10-2 freight locomotive with 60 inches (1,524 millimetres) coupled wheels. At the time, however, the demand for general utility locomotive types was so pronounced that no good argument could be put forward for the introduction of a heavy locomotive dedicated to goods working only. Another factor which acted against the project was the insufficient length of the receiving sidings in the yards, which made it doubtful that such a locomotive would have been able to be used to its full capacity.^[5]

Although the Class 22 was never built, the class number was not used for another steam locomotive type.^[5]

Service

Class 21 number 2551 was mainly used on the line from Pretoria to the Eastern Transvaal and was scrapped in 1952 after only 15 years in service. During its time in service it was equipped with smoke deflectors. Neither the Class 21 nor the aborted Class 22 design was subsequently repeated in either its original or modified form, leaving the impression that they represented advanced thinking that appears to have been considered as too far and too fast by Watson’s successors.^[3]

During World War II this locomotive was often used to haul long and heavy military trains and it was made the official mascot of the then oldest military unit in Pretoria, the Pretoria Regiment (Princess Alice's Own). The Class 21 was the only SAR locomotive to be honoured in this way by the military.^[6]

Illustration

The main picture shows no. 2551 with smoke deflectors installed, circa 1945, while the following photographs show both sides of the locomotive in the factory gray livery it was delivered in.

References

1 2 3 4 5 6 7 8 Holland, D.F. (1972). Steam Locomotives of the South African Railways, Volume 2: 1910-1955 (1st ed.). Newton Abbott, Devon: David & Charles. pp. 73–76. ISBN 978-0-7153-5427-8.
↑ South African Railways and Harbours Locomotive Diagram Book, 2’0” & 3’6” Gauge Steam Locomotives, 15 August 1941, as amended
1 2 3 4 5 6 7 8 9 Paxton, Leith; Bourne, David (1985). Locomotives of the South African Railways (1st ed.). Cape Town: Struik. pp. 10–11, 74–75. ISBN 0869772112.
↑ North British Locomotive Company works list, compiled by Austrian locomotive historian Bernhard Schmeiser
1 2 3 4 5 6 Durrant, A E (1989). Twilight of South African Steam (1st ed.). Newton Abbott, London: David & Charles. p. 37. ISBN 0715386387.
↑ The Rayton-Cullinan Railway Line and World War 2, Lieutenant-Colonel J.E. Samuels (SANDF, Ret), Bulletin of the Railway History Group, No. 82, December 2005

Wikimedia Commons has media related to South African Class 21 (2-10-4).

Locomotives of South Africa

Steam

7' ¼" gauge	East London Harbour 0-4-0 Table Bay Harbour 0-4-0ST Table Bay Harbour 0-4-0T Table Bay Harbour 0-4-0WT

4' 8½" gauge	Cape 0-4-0T Blackie Cape 0-4-2 Cape 2-4-0T CGR 0-4-0ST Aid Natal 0-4-0ST Durban Natal 0-4-0WT Natal Natal 4-4-0T Perseverance

3' 6" gauge Tank engines	CGR 0-4-0ST 1873 CGR 0-4-0ST 1874 CGR 0-4-0ST 1881 Coffee Pot CGR 0-6-0ST 1902 CGR 0-6-0T 1876 Back-to-Back CGR 2-6-0ST 1900 CGR 2-6-0ST 1902 CGR 1st Class 0-4-0ST 1875 CGR 1st Class 0-4-0ST 1876 CGR 1st Class 2-6-0ST 1876 CGR 1st Class 4-4-0T 1875 CGR 2nd Class 4-4-0T 1882 CGR 3rd Class 2-6-0T CGR Railmotor CSAR Class C CSAR Class E CSAR Rack CSAR Railmotor DSWA Eight-Coupled Tank 2-8-0T Durban's Congella Durban's Edward Innes Durban's John Milne Durban's Sir Albert Port Elizabeth Harbour 0-4-0ST Kowie Railway 0-6-0T Kowie Railway 4-4-0T Metropolitan & Suburban 4-6-2T NGR 2-6-0T Durban & Pietermaritzburg NGR Class I 2-6-2T NGR Class K 0-4-0ST NGR Class K 0-6-0ST NGR Class K 2-6-0T NZASM 10 Tonner NZASM 14 Tonner NZASM 18 Tonner NZASM 19 Tonner NZASM 32 Tonner NZASM 40 Tonner PPR 26 Tonner PPR 35 Tonner Portuguese SAR 0-4-0ST 1903 SAR 0-4-0T no. 69 SAR Class A SAR Class B SAR Class C SAR Class C1 SAR Class C2 SAR Class D SAR Class E SAR Class F SAR Class G SAR Class H SAR Class H1 SAR Class H2 SAR Class J SAR Class K SAR Clayton Railmotor

3' 6" gauge Tender engines	CGR 1st Class 2-6-0 1876 Beyer, Peacock CGR 1st Class 2-6-0 1876 Kitson CGR 1st Class 2-6-0 1879 CGR 1st Class 2-6-0 1891 CGR 1st Class 4-4-0 1879 CGR 1st Class 4-4-0TT 1881 CGR 2nd Class 2-6-2TT 1875 CGR 3rd Class 4-4-0 1883 CGR 3rd Class 4-4-0 1884 CGR 3rd Class 4-4-0 1889 CGR 3rd Class 4-4-0 1898 CGR 3rd Class 4-4-0 1901 CGR 3rd Class 4-4-0 1903 CGR 4th Class 4-4-2 CGR 4th Class 4-6-0TT 1880 CGR 4th Class 4-6-0TT 1882 CGR 4th Class 4-6-0TT 1884 CGR 5th Class 4-6-0 1890 CGR 5th Class 4-6-0 1891 DSWA Eight-Coupled Tender 2-8-0 NGR Havelock NGR Class I SAR Class Exp 1 SAR Class Exp 2 SAR Class Exp 3 SAR Class Exp 4 SAR Class Exp 5 SAR Class Exp 6 SAR Class S SAR Class S1 SAR Class S2 SAR Class 1 SAR Class 1A SAR Class 1B SAR Class 2 SAR Class 2C SAR Class 3 SAR Class 3A SAR Class 3B SAR Class 4 SAR Class 4A SAR Class 5 SAR Class 5A SAR Class 5B SAR Class 6 SAR Class 6A SAR Class 6B SAR Class 6C SAR Class 6D SAR Class 6E SAR Class 6F SAR Class 6G SAR Class 6H SAR Class 6J SAR Class 6K SAR Class 6L SAR Class 6Y SAR Class 6Z SAR Class 7 SAR Class 7A SAR Class 7B SAR Class 7C SAR Class 7D SAR Class 7E SAR Class 7F SAR Class 8 SAR Class 8A SAR Class 8B SAR Class 8C SAR Class 8D SAR Class 8E SAR Class 8F SAR Class 8R SAR Class 8X SAR Class 8Y SAR Class 8Z SAR Class 9 SAR Class 10 SAR Class 10A SAR Class 10B SAR Class 10C SAR Class 10D SAR Class 11 SAR Class 12 SAR Class 12A SAR Class 12B SAR Class 13 SAR Class 14 SAR Class 14A SAR Class 14B SAR Class 14C SAR Class 15 SAR Class 15A SAR Class 15B SAR Class 15C SAR Class 15CA SAR Class 15E SAR Class 15F SAR Class 16 SAR Class 16A SAR Class 16B SAR Class 16C SAR Class 16D SAR Class 16DA SAR Class 16E SAR Class 17 SAR Class 18 SAR Class 19 SAR Class 19A SAR Class 19B SAR Class 19C SAR Class 19D SAR Class 20 SAR Class 21 SAR Class 23 SAR Class 24 SAR Class 25 SAR Class 25NC SAR Class 26 Red Devil

3' 6" gauge Articulated engines	CGR Fairlie CGR Kitson-Meyer SAR Class FC SAR Class FD SAR Class GA SAR Class GB SAR Class GC SAR Class GCA SAR Class GD SAR Class GDA SAR Class GE SAR Class GEA SAR Class GF SAR Class GG SAR Class GH SAR Class GK SAR Class GL SAR Class GM SAR Class GMA SAR Class GO SAR Class HF SAR Class KM SAR Class MA SAR Class MB SAR Class MC SAR Class MC1 SAR Class MD SAR Class ME SAR Class MF SAR Class MG SAR Class MH SAR Class MJ SAR Class MJ1 SAR Class U

2' 6" gauge	Cape Copper 0-6-0T 1871 Cape Copper Britannia Cape Copper Caledonia Cape Copper Clara Class Cape Copper Condenser Cape Copper Scotia Class Namaqua Copper Pioneer

2' & 600mm gauges	ACR Class NG-G16A CGR NG 0-6-0T CGR NG 4-6-2T CGR Type A 2-6-4T CGR Type C 0-4-0T DSWA Class Ha DSWA Class Hb DSWA Class Hc DSWA Class Hd DSWA Jung DSWA Zwillinge NGR Class N 4-6-2T SAR NG 0-4-0T 1899 SAR Class NG1 SAR Class NG2 SAR Class NG3 SAR Class NG4 SAR Class NG5 SAR Class NG6 SAR Class NG7 SAR Class NG8 SAR Class NG9 SAR Class NG10 SAR Class NG-G11 SAR Class NG-G12 SAR Class NG-G13 SAR Class NG-G14 SAR Class NG15 SAR Class NG-G16

Electric

Amcoal Class E38

Diesel

3' 6" gauge Diesel-electric	PRASA Class Afro 4000 SAR Class DS SAR Class DS1 SAR Class 31-000 SAR Class 32-000 SAR Class 32-200 SAR Class 33-000 SAR Class 33-200 SAR Class 33-400 SAR Class 34-000 SAR Class 34-200 SAR Class 34-400 SAR Class 34-500 SAR Class 34-600 SAR Class 34-800 SAR Class 34-900 SAR Class 35-000 SAR Class 35-200 SAR Class 35-400 SAR Class 35-600 SAR Class 36-000 SAR Class 36-200 SAR Class 37-000 Spoornet Class 39-000 TFR Class 35-800 TFR Class 39-200 TFR Class 43-000 TFR Class 44-000

2' gauge Diesel-electric	SAR Class 91-000

3' 6" gauge Diesel-hydraulic	SAR Class 61-000

3' 6" gauge Electro-diesel	Spoornet Class 38-000

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