South African Class 12A 4-8-2

South African Class 12A & 12AR 4-8-2

300px Class 12AR no. 1535 at Maraisburg, 27 April 2009

Type and origin ♠ Class 12A as built with a Belpaire firebox ♥ Class 12AR rebuilt with a round-topped firebox Power type Steam Designer South African Railways (D.A. Hendrie) Builder North British Locomotive Company Henschel and Son Serial number NBL 21738-21757, 22751-22765, 23891-23903 Henschel 21046-21051, 21428-21440 Model Class 12A Build date 1919-1929 Total produced 75

Specifications Configuration 4-8-2 (Mountain) Driver axle 2nd coupled axle Gauge 3 ft 6 in (1,067 mm) Cape gauge Leading dia Coupled dia 51 in (1,295 mm) Trailing dia 33 in (838 mm) Tender wheels 34 in (864 mm) Wheelbase  • Engine 32 ft 1 in (9,779 mm)  • Leading 6 ft 2 in (1,880 mm)  • Coupled 13 ft 6 in (4,115 mm)  • Tender 16 ft 9 in (5,105 mm)  • Tender bogie 4 ft 7 in (1,397 mm) Length Height ♠ 12 ft 10 in (3,912 mm) ♥ 13 ft (3,962 mm) Frame type Plate Axle load ♠ ♥  • Leading ♠ ♥  • 1st coupled ♠ ♥  • 2nd coupled ♠ ♥  • 3rd coupled ♠ ♥  • 4th coupled ♠ ♥  • Trailing ♠♥  • Tender bogie Bogie 1: Bogie 2:  • Tender axle Adhesive weight ♠ ♥ Loco weight ♠ ♥ Tender weight Loco & tender weight ♠ ♥ 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 Boiler:  • Pitch ♠ 7 ft 9 in (2,362 mm) ♥ 8 ft 6 in (2,591 mm)  • Diameter ♠ ♥ 6 ft (1,829 mm)  • Tube plates ♠ 18 ft (5,486 mm) ♥ 19 ft 4 in (5,893 mm)  • Small tubes ♠ 159: ♥ 119:  • large tubes ♠ 24 ♥ 30:  • Firebox type ♠ Belpaire - ♥ Round-top Boiler pressure ♠♥ 190 psi (1,310 kPa) Safety valve ♠ Ramsbottom - ♥ Ross Pop Firegrate area ♠ 40.5 sq ft (3.76 m2) ♥ 41 sq ft (3.8 m2) Heating surface ♠ 2,510 sq ft (233 m2) ♥ 2,502 sq ft (232.4 m2)  • Tubes ♠ 2,301 sq ft (213.8 m2) ♥ 2,338 sq ft (217.2 m2)  • Firebox ♠ 209 sq ft (19.4 m2) ♥ 164 sq ft (15.2 m2) Superheater:  • Heating area ♠ 466 sq ft (43.3 m2) ♥ 480 sq ft (45 m2) Cylinders Two Cylinder size 24 in (610 mm) bore 26 in (660 mm) stroke Valve gear Walschaerts Valve type Piston Couplers Bell link-and-pin AAR knuckle (1950s)

Performance figures Tractive effort ♠♥ 41,840 lbf (186.1 kN) @ 75%

Career Operators South African Railways Class Class 12A & 12AR Number in class SAR 67, Industrial 8 Numbers 1520-1550, 2103-2138 Delivered 1919-1929 First run 1919 Withdrawn 1980s

The leading coupled axle had flangeless wheels

The South African Railways Class 12A 4-8-2 of 1919 was a steam locomotive.

Between 1919 and 1929, the South African Railways placed 67 Class 12A steam locomotives with a 4-8-2 Mountain type wheel arrangement in service. Eight were also built for industrial use between 1947 and 1953.

Manufacturers

The Class 12A was the final locomotive design by D.A. Hendrie, Chief Mechanical Engineer (CME) of the South African Railways (SAR) from 1910 to 1922, and one of his finest. It was an improved and larger version of his Class 12 locomotive, with larger diameter cylinders to increase tractive effort and a redesigned boiler.

Between 1919 and 1929, altogether 67 of them were built on five orders, 48 by the North British Locomotive Company (NBL) in Scotland and 19 by Henschel and Son in Kassel, Germany.

• The first twenty were built by NBL and were delivered in 1919, numbered in the range from 1520 to 1539.
• These were followed by another fifteen from NBL, which were built in late 1919, but were only delivered in 1921, numbered in the range from 2111 to 2125.
• The Henschel-built locomotives only arrived several years later. Six were delivered in 1928 and numbered in the range from 1540 to 1545.
• Another thirteen were delivered by Henschel in 1929, numbered in the ranges from 1546 to 1550 and 2103 to 2110, filling the gaps in the numbering sequence.
• The final thirteen, once again built by NBL, were also delivered in 1929 and numbered in the range from 2126 to 2138.

Characteristics

File:D.A. Hendrie.jpg

D.A. Hendrie

The locomotives were built on thick plate frames. They were superheated and had Walschaerts valve gear and Belpaire fireboxes, which included combustion chambers. At the time, these locomotives were of the maximum size permissible for the Mountain type on Cape gauge. They were designed primarily to supplement the Class 12 locomotives which were already working on the coal line between Witbank and Germiston.

The original Class 12A superheater header was arranged with the Gresley type air valve, which was introduced to prevent the risk of superheater elements being burned or damaged by overheating while engines were drifting. The valve automatically opened when the regulator was closed and allowed outside air to be drawn into the superheater elements. Even though experience showed that the heated air which then entered the steam chests and cylinders was harmful to cylinder lubrication, with no apparent effect on the life of the superheater elements, it was some years before the use of these air valves was finally discontinued.

Reboilering

During the 1930s, many serving locomotives were reboilered with a standard boiler type, designed by then CME A.G. Watson as part of his standardisation policy. In the process, they were then also equipped with Watson cabs, with their distinctive slanted fronts, compared to the conventional vertical fronts of the original cabs. Such Watson Standard reboilered locomotives were reclassified by adding an "R" suffix to their classification.

File:Class 12A 1548 (4-8-2).JPG

When Class 12A locomotives numbers 1540 and 2135 became the first to be reboilered in 1943, however, none of the Watson Standard boilers were deemed suitable, since the Watson Standard no. 2 series were too small, while the no. 3 series were too large. A special boiler was therefore designed for them by Dr. M.M. Loubser, the CME at the time. These boilers did not conform to any of the Watson Standard boilers and were a totally new type of rather massive proportions which, on a locomotive with relatively small coupled wheels, created an impression of great power. Certain features common to the Watson Standard boilers were incorporated in the design, however, since it was deemed necessary to have the greatest possible degree of interchangeability of parts with those of the Watson Standard boilers.

Unlike the orignal Class 12A boilers, initial and in-service repair cost considerations led to the Loubser boiler being built without a combustion chamber. The round-top firebox was radially stayed and the first two rows of stays were flexible. Similar stays were fitted in the side, back and throat plates and in the breaking zones. There were eight cross stays over the top of the firebox, which was of steel.

The original Belpaire boilers were fitted with Ramsbottom safety valves, while, like the Watson Standard boilers, the Loubser boiler was fitted with two Ross pop safety valves. Feedwater was supplied by two Davies and Metcalf injectors through a top-feed arrangement. At the firebox, the boiler was carried by a vertical transverse plate at the back, and at the two front corners by sliding grease-lubricated shoes which rested on gunmetal liner plates which, in turn, were fixed to specially-designed steel brackets, welded to the inside of the bridle casting. The boiler barrel was attached to the engine frame by four diaphragm plates, bolted to "T" sections which were riveted to the barrel.

File:Susancabside.jpg

140px

Altogether 44 Class 12A locomotives were eventually reboilered with Loubser boilers and reclassified to Class 12AR. During the reboilering, which included the installation of Watson cabs, the locomotives were also equipped with a longer smokebox, which resulted in the distinctive appearance of the Class 12AR. Like the Watson Standard boilers, the Loubser boilers also have the distinctive rectangular regulator cover, just to the rear of the chimney. In the case of the Classes 12A and 12AR locomotives, three even more obvious differences are the extended smokebox, the Watson cab and the absence of the Belpaire firebox hump between the cab and boiler on the reboilered locomotives.

The reboilered locomotives were considered by some enginemen to be inferior steamers, compared to the as-built engines. A shortened version of Loubser's Class 12AR boiler was later used on the new Class S1 shunting locomotives.

Service

South African Railways

When new, the Class 12A locomotives were placed in service hauling coal on the section from Witbank to Germiston. The unreboilered locomotives spent a large part of their working lives in Transvaal, mainly in Western Transvaal and shedded at Springs and Germiston, a few in Eastern Transvaal and shedded at Nelspruit and Waterval Boven, and one at De Aar in the Cape Province. In 1977, all the Class 12A locomotives were relocated to the Cape Northern system for shunting at De Aar and at Beaconsfield in Kimberley.

The more numerous reboilered Class 12AR locomotives worked throughout most parts of South Africa, being shedded at Kimberley, De Aar, Port Elizabeth and East London in the Cape Province, Glencoe and Newcastle in Natal, Klerksdorp in Transvaal and Kroonstad in the Orange Free State.

The Classes 12A and 12AR versions both proved to be very successful engines which performed well, with low repair costs. Modifications in design of details after entering service were negligible.

Industrial service

None of the SAR Class 12A or Class 12AR locomotives were sold into industrial service, but between 1947 and 1953, eight Class 12A locomotives, similar to the unreboilered SAR locomotives but without superheaters, were built new for industrial service by NBL.

Works numbers

The builders, years built, works numbers and reboilering particulars are listed in the table.

Class 12A 4-8-2
Builders, works numbers and reboilering

Builder	Year built	Works no.	SAR no.	Class
NBL	1919	21738	1520	12AR
NBL	1919	21739	1521	12A
NBL	1919	21740	1522	12AR
NBL	1919	21741	1523	12AR
NBL	1919	21742	1524	12A
NBL	1919	21743	1525	12A
NBL	1919	21744	1526	12A
NBL	1919	21745	1527	12A
NBL	1919	21746	1528	12A
NBL	1919	21747	1529	12AR
NBL	1919	21748	1530	12AR
NBL	1919	21749	1531	12A
NBL	1919	21750	1532	12AR
NBL	1919	21751	1533	12A
NBL	1919	21752	1534	12AR
NBL	1919	21753	1535	12AR
NBL	1919	21754	1536	12AR
NBL	1919	21755	1537	12AR
NBL	1919	21756	1538	12A
NBL	1919	21757	1539	12A
Henschel	1928	21046	1540	12AR
Henschel	1928	21047	1541	12AR
Henschel	1928	21048	1542	12AR
Henschel	1928	21049	1543	12AR
Henschel	1928	21050	1544	12AR
Henschel	1928	21051	1545	12AR
Henschel	1929	21428	1546	12AR
Henschel	1929	21429	1547	12A
Henschel	1929	21430	1548	12A
Henschel	1929	21431	1549	12AR
Henschel	1929	21432	1550	12AR
Henschel	1929	21433	2103	12AR
Henschel	1929	21434	2104	12AR
Henschel	1929	21435	2105	12AR
Henschel	1929	21436	2106	12A
Henschel	1929	21437	2107	12A
Henschel	1929	21438	2108	12AR
Henschel	1929	21439	2109	12AR
Henschel	1929	21440	2110	12AR
NBL	1921	22751	2111	12A
NBL	1921	22752	2112	12AR
NBL	1921	22753	2113	12AR
NBL	1921	22754	2114	12A
NBL	1921	22755	2115	12AR
NBL	1921	22756	2116	12AR
NBL	1921	22757	2117	12A
NBL	1921	22758	2118	12AR
NBL	1921	22759	2119	12AR
NBL	1921	22760	2120	12AR
NBL	1921	22761	2121	12AR
NBL	1921	22762	2122	12AR
NBL	1921	22763	2123	12A
NBL	1921	22764	2124	12AR
NBL	1921	22765	2125	12AR
NBL	1929	23891	2126	12A
NBL	1929	23892	2127	12AR
NBL	1929	23893	2128	12AR
NBL	1929	23894	2129	12AR
NBL	1929	23895	2130	12A
NBL	1929	23896	2131	12AR
NBL	1929	23897	2132	12AR
NBL	1929	23898	2133	12A
NBL	1929	23899	2134	12A
NBL	1929	23900	2135	12AR
NBL	1929	23901	2136	12AR
NBL	1929	23902	2137	12AR
NBL	1929	23903	2138	12A

Illustration

The main picture shows preserved NBL-built Class 12AR no. 1535 Susan at Maraisburg station during a Reefsteamers excursion on 27 April 2009.

• Class 12A 2111 (4-8-2) Playing Cards.jpg

  NBL-built 12A no. 2111, as built with Type MP1 tender, c. 1921

• SAR Class 12A 1526 De Aar 060479.jpg

  NBL-built 12A no. 1526 at De Aar, Cape Province, 6 April 1979

• SAR Class 12A 1547 Visrivier - 140479.jpg

  Henschel-built 12A no. 1547 at Visrivier, 14 April 1979

• SAR Class 12AR 1542 Kimberley 270383.jpg

  Henschel-built 12AR no. 1542 at Kimberley, 27 March 1983

• SAR Class 12AR 2110 Kaserne 070479.jpg

  Last Henschel-built 12AR no. 2110 at Kaserne, 7 April 1979