South African Class 12A 4-8-2

South African Railways Class 12A

Company type	Steam locomotive class
Industry	Rail transport
Founded	1919
Headquarters	South Africa
Products	Steam locomotives

South African Railways Class 12A 4-8-2 Steam Locomotive

The Class 12A steam locomotive, featuring a 4-8-2 Mountain wheel configuration, was introduced by the South African Railways starting in 1919.

Over the period from 1919 to 1929, a total of 67 Class 12A locomotives were commissioned and operated by the South African Railways. Additionally, between 1947 and 1953, another eight units of this class were constructed specifically for industrial applications.

Manufacturers

The Class 12A locomotive represented the last design crafted by D.A. Hendrie, who served as the Chief Mechanical Engineer (CME) of the South African Railways (SAR) from 1910 until 1922, and is considered among his most accomplished works. This model was a larger and enhanced iteration of his earlier Class 12 engine, featuring cylinders of greater diameter to boost tractive force along with a redesigned boiler.

Over the period from 1919 to 1929, a total of 67 units were produced across five separate orders. Of these, 48 were constructed by the North British Locomotive Company (NBL) located in Scotland, while the remaining 19 were manufactured by Henschel and Son in Kassel, Germany.

• The initial batch of twenty locomotives was built by NBL and delivered in 1919, assigned numbers ranging from 1520 to 1539.
• Following this, another fifteen units from NBL were assembled late in 1919 but only reached delivery in 1921, numbered between 2111 and 2125.
• The Henschel-built machines arrived somewhat later; six were supplied in 1928 with numbers from 1540 to 1545.
• In 1929, Henschel delivered an additional thirteen locomotives, filling numbering gaps with units numbered from 1546 to 1550 and from 2103 to 2110.
• The final thirteen locomotives, again produced by NBL, were also delivered in 1929 and bore numbers ranging from 2126 to 2138.

Characteristics

At the time of their introduction, these locomotives represented the largest size allowable for Mountain-type engines on the Cape gauge. Their primary purpose was to augment the existing Class 12 fleet operating on the coal route between Witbank and Germiston. Due to their slightly increased axle load compared to the earlier Class 12, they were expected to handle heavier loads on that section of track.

File:D.A. Hendrie.jpg

D.A. Hendrie

These engines featured 1+1⁄2-inch thick (38-millimetre) thick plate frames. They were designed with superheating technology and incorporated piston valves, Walschaerts valve gear, and Belpaire fireboxes equipped with combustion chambers. The boilers on the first two production runs (1919 and 1921) utilized Ramsbottom safety valves; however, photographic evidence of later batches indicates they employed Ross pop safety valves instead. From the third batch onward, feedwater was supplied via a top feed system using copper piping running from each side’s running boards up to the boiler ahead of the steam dome.

The initial Class 12A superheater header included a Gresley type air valve designed to prevent damage or burning of superheater elements during drifting by automatically admitting outside air when the regulator was closed. Although it was later found that this heated air negatively affected cylinder lubrication without benefiting superheater longevity, it took several years before these air valves were discontinued.

The first two batches delivered in 1919 and 1921 came equipped with the traditional Johnston link-and-pin couplers that had been standard since the inception of the Cape Government Railways in 1873. By the time production resumed with the third batch in 1928, SAR had begun transitioning its Cape Gauge rolling stock to AAR knuckle couplers, so locomotives from the third through fifth batches were supplied with this updated coupling system.

Tenders

Upon delivery, the locomotives came equipped with two distinct tender models: the Types MP1 and MT. Although documentation does not definitively specify which Class 12A production runs received each tender type, archival builder's photographs reveal that the NBL-produced units from 1919 and 1921 were paired with Type MP1 tenders, whereas those constructed by Henschel and later by NBL featured Type MT tenders.

Type MP1 tender

The Type MP1 tender is characterized by its coal bunker sides being distinctly separate at the top, mounted within the upper rim of the water tank. This tender held up to 10 long tons (10.2 tonnes) of coal and carried 4,250 imperial gallons (19,300 litres) of water, with an axle load rated at approximately 13 long tons 15 hundredweight (13,970 kilograms).

A number of these tenders were later reconstructed into smooth-sided Type MR tenders, which featured an increased water capacity of 4,600 imperial gallons (20,900 litres) and a slightly reduced axle load near 13 long tons 14 hundredweight (13,920 kilograms).

Type MT tender

The Type MT tender was a heavier model distinguished by its smooth sides extending fully to the coal bunker’s top edge. It accommodated a coal load of 12 long tons (12.2 tonnes) and a water volume of 6,000 imperial gallons (27,300 litres), carrying an axle load around 16 long tons 11 hundredweight (16,820 kilograms).

Reboilering

Throughout the 1930s, numerous locomotives in operation underwent reboilering with a standardized boiler design developed by then Chief Mechanical Engineer A.G. Watson. This initiative was part of his broader standardisation strategy. Alongside reboilering, these engines were fitted with Watson cabs, notable for their slanted fronts in contrast to the original cabs’ vertical fronts. Locomotives modified in this manner were reclassified by appending an "R" suffix to their original classification.

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

In 1943, when Class 12A units numbered 1540 and 2135 became the first to be reboilered, none of the existing Watson Standard boilers proved appropriate—the no. 2 series was undersized while the no. 3 series was oversized. Consequently, Dr. M.M. Loubser, then CME, designed a bespoke boiler for these locomotives. This new boiler did not conform to any Watson Standard types and was substantially larger, lending the locomotive an imposing appearance given its relatively small coupled wheels. Nevertheless, certain elements typical of Watson Standard boilers were integrated to maximize parts interchangeability. The boiler’s dimensions fell between those of the no. 2 and no. 3 Watson Standard models.<ref name="SAR&H Jul 1946">

Unlike the initial Class 12A boilers, cost considerations during construction and maintenance led to omitting a combustion chamber in Loubser’s design. The round-top firebox was supported by radial stays, with flexible stays installed in the first two rows. Similar stays reinforced the side, back, and throat plates as well as stress-prone areas. Eight cross stays spanned over the steel firebox’s top.

While the original Belpaire boilers utilized Ramsbottom safety valves, both Watson Standard and Loubser boilers employed two 3+1⁄2 inches (89 millimetres) Ross pop safety valves. Feedwater was delivered via two Davies and Metcalf injectors through a top-feed system. The boiler rested at the rear on a vertical transverse plate and at its front corners on sliding grease-lubricated shoes seated on gunmetal liners attached to steel brackets welded inside the bridle casting. The barrel was fastened to the engine frame using four diaphragm plates bolted onto riveted "T" sections on the barrel itself.

File:Susancabside.jpg

Ultimately, forty-four Class 12A locomotives were converted with Loubser boilers and redesignated as Class 12AR. The reboilering process included fitting Watson cabs and extending the smokebox length, giving these locomotives their distinctive profile. Similar to Watson Standard boilers, Loubser’s design featured a rectangular regulator cover positioned just behind the chimney. Among Classes 12A and 12AR, three particularly noticeable distinctions are the elongated smokebox, adoption of Watson cabs, and absence of the Belpaire firebox hump between cab and boiler on reboilered units.

Some locomotive operators regarded the reboilered versions as less efficient steamers compared to their original counterparts. A shortened adaptation of Loubser’s Class 12AR boiler design was later applied to new Class S1 shunting engines.

South African Railways

Upon introduction, the Class 12A locomotives were initially assigned to haul coal between Witbank and Germiston. These locomotives, prior to receiving reboilering, spent much of their operational lifespan within Transvaal, predominantly in Western Transvaal, with allocations at the depots in Springs and Germiston. A smaller number operated in Eastern Transvaal, based at Nelspruit and Waterval Boven, while one unit was stationed at De Aar in the Cape Province. The class also saw service in Natal during the late 1920s, likely following the substantial arrival of Class 15CA locomotives in 1929. In this region, they demonstrated greater hauling capacity by managing two additional coaches compared to a Class 14 on the mainline connecting Durban and Pietermaritzburg in 1921. Notably, a Class 12A locomotive led the final steam-powered mainline passenger train departing Durban station after electric traction was introduced between Pietermaritzburg and Durban in 1936. By 1977, all surviving Class 12A engines were transferred to the Cape Northern system for shunting duties at De Aar and Beaconsfield in Kimberley.

The reboilered Class 12AR locomotives, which were more numerous, operated extensively across South Africa. Their allocations included depots such as Kimberley, De Aar, Port Elizabeth, and East London within the Cape Province; Glencoe and Newcastle in Natal; as well as Klerksdorp in Transvaal and Kroonstad in the Orange Free State. Both East London and Port Elizabeth received four units each; those assigned to Port Elizabeth bore engine numbers 1544, 1545, 2125, and 2129 and were deployed on the swift Saturday morning passenger services bound for Cape Town.

Both Class 12A and Class 12AR models earned reputations as highly effective locomotives characterized by dependable performance and minimal maintenance expenses. Post-delivery design alterations were scarce.

Industrial service

None of the SAR Class 12A or Class 12AR locomotives transitioned into industrial use. However, between 1947 and 1953, eight new locomotives resembling the unreboilered SAR Class 12A but lacking superheaters were constructed by NBL specifically for industrial applications.

Works numbers

The table below details the manufacturers, production years, works numbers, reboilering status, and original tender classifications.

... (table continues with same formatting) ...

Preservation

Class 12A 4-8-2
Manufacturers, works numbers, classification & original tender type

Builder	Year built	Works number	SAR number	Class	Tender type
NBL	1919	21738	1520	12AR	MP1
NBL	1919	21739	1521	12A	MP1
NBL	1919	21740	1522	12AR	MP1
NBL	1919	21741	1523	12AR	MP1
NBL	1919	21742	1524	12A	MP1
NBL	1919	21743	1525	12A	MP1
NBL	1919	21744	1526	12A	MP1
NBL	1919	21745	1527	12A	MP1
NBL	1919	21746	1528	12A	MP1
NBL	1919	21747	1529	12AR	MP1
NBL	1919	21748	1530	12AR	MP1
NBL	1919	21749	1531	12A	MP1
NBL	1919	21750	1532	12AR	MP1

Class	Quantity	Works Number	THF / Private	Leased / Owner	Present Location	Outside South Africa	?
12R	1865	BP 5994	Private		Kimberley Locomotive Depot
12R	1947	BALDWIN 52754	THF	Reefsteamers	Germiston Locomotive Depot
12R	1505	NBL 20176	THF	Umgeni Steam Railway	Kloofstation (Inchaga)
12A	2111	NBL 22751	THF		Bloemfontein Locomotive Depot
12AR	1535	NBL 21753	THF	Reefsteamers	Germiston Locomotive Depot

Illustration

• NBL builder’s photograph of locomotive no. 1520, first series, equipped with Type MP1 tender, circa 1919. Notice the missing top-feed feedwater arrangement.
  NBL builder’s photograph of locomotive no. 1520, first series, equipped with Type MP1 tender, circa 1919. Notice the missing top-feed feedwater arrangement.
• Unit no. 2111 from the second series, fitted with Ramsbottom safety valves and Type MP1 tender, around 1921
  Unit no. 2111 from the second series, fitted with Ramsbottom safety valves and Type MP1 tender, around 1921
• Henschel builder’s image of no. 1543, third series, featuring pop valves, top-feed feedwater system, and Type MT tender, circa 1928
  Henschel builder’s image of no. 1543, third series, featuring pop valves, top-feed feedwater system, and Type MT tender, circa 1928
• Photograph of no. 1548 from the fourth batch by Henschel, showing pop valves and Type MT tender, approximately 1929
  Photograph of no. 1548 from the fourth batch by Henschel, showing pop valves and Type MT tender, approximately 1929
• NBL builder’s photo of no. 2131, fifth series, with pop valves and Type MT tender, around 1929
  NBL builder’s photo of no. 2131, fifth series, with pop valves and Type MT tender, around 1929
• NBL-produced Class 12A no. 1526 at De Aar, paired with Type MR tender, dated April 6, 1979
  NBL-produced Class 12A no. 1526 at De Aar, paired with Type MR tender, dated April 6, 1979
• Henschel-built Class 12A no. 1547 stationed at Visrivier on April 14, 1979
  Henschel-built Class 12A no. 1547 stationed at Visrivier on April 14, 1979
• Henschel-manufactured Class 12AR no.1542 at Kimberley on March 27,1983
  Henschel-manufactured Class 12AR no.1542 at Kimberley on March 27,1983