Watson Standard boilers

The Class 19D was delivered with a Watson Standard no. 1A boiler, fitted with Ross Pop safety valves and set at 200 pounds per square inch (1,379 kilopascals) pressure. The regulator was of the multiple-valve type, with the valves arranged on the saturated steam side of the superheater header in accordance with SAR practice. The boiler was one of the range of standard type boilers which were designed by Day's predecessor as CME, A.G. Watson, as part of his standardisation policy. The locomotive was also equipped with a Watson cab with its distinctive inclined front.^{[1][2][4][10][11]}

Despite the specifications, the first batch of Class 19D locomotives, built by Krupp and Borsig and delivered in 1937 and 1938, came in two variations. The Krupp-built locomotives were delivered with domeless boilers, while the Borsig-built locomotives conformed to the specifications with domed boilers.^[1][2][4]

While the domeless boilers did not conform to the specified Watson Standard no. 1A boiler as far as the dome was concerned, they were accepted nevertheless, probably since all their other dimensions were identical to that of the Watson Standard boiler. It appears that Krupp had decided on their own accord that a dome was not necessary since there was no regulator in the dome, but merely a standpipe. Krupp substituted the dome with a manhole cover on which the two Pop safety valves were mounted, while the steam was collected through a battery of collecting pipes, situated high up in the boiler in a similar manner to that which was used in the Class 16E.^[1][2]

All the subsequent Class 19D orders were delivered with domed Watson Standard no. 1A boilers with the usual standpipe steam collector high up in the dome, from where steam was led to the multi-valve regulator in the smokebox. Technically, whenever the loading gauge permitted the use of domes, their use was preferable to the domeless system which resulted in crowding multiple pipes into the boiler and other complications better left out of boilers. Operationally, according to drivers, there was no apparent difference in locomotive performance between the two boiler types.^[1][2][13]

The Watson Standard boilers are interchangeable between locomotives. In the process of locomotives undergoing major overhauls, these twenty Krupp-built domeless boilers migrated between engines during subsequent years. As a result, locomotives from the other builders and even some Classes 19A and 19C locomotives eventually ended up with some of these domeless boilers.^[4]

Tenders

As a result of having been built over such a long time span by so many different manufacturers, the six main groups of the Class 19D all had different all-up weights and axle loadings, as shown in the table and the specifications in the infobox. Over the eleven years during which the Class 19D was being produced for the SAR, some alterations occurred.^[1][10][11]

• As built, the Class 19D was delivered with Type MT tenders with a 12 long tons (12.2 tonnes) coal and a 6,000 imperial gallons (27,300 litres) water capacity, even though the axle load of 16 long tons 11 hundredweight (16,820 kilograms) of these tenders exceeded the permissible limits on the branch lines for which the Class 19D was intended. Upon delivery, their new Type MT tenders were exchanged for the smaller modified Type MP1 tenders from some of the reboilered mainline locomotives. The Type MP1, many of which were later rebuilt to Type MR tenders, had a lighter axle load of 13 long tons 15 hundredweight (13,970 kilograms) and was therefore more suitable for branch line work. This policy was followed with all the Classes 19B, 19C and 19D, except the last batch of Class 19D for the SAR, numbers 3321 to 3370.^[1][2]
• During 1944 Dr. M.M. Loubser, then CME, who had been involved with the design of the Class 19 family from the very beginning in the late 1920s, made further improvements to the Class 19D. All the post-war locomotives came equipped with vacuum brake systems in addition to the steam brakes. The two 21 inches (533 millimetres) vacuum cylinders were fitted under the running boards on either side at a point about midway between the leading and driving coupled wheels, while the vacuum chamber was arranged in line with the intermediate coupled wheels.^[1][2]
• The final batch from NBL, numbers 3321 to 3370, had Type MX tank wagon type tenders with cylindrical water tanks, similar in appearance to the American Vanderbilt type tenders. They were built to the design of Dr. M.M. Loubser, ran on three-axle Buckeye bogies and became commonly known as Torpedo tenders.^[1][4]

South African Railways

During the service life of the Class 19D, several tender exchanges occurred to best equip a locomotive for the region it was allocated to and the type of service it was to be employed in. In line service, type MX Torpedo tenders were usually preferred for their larger coal and water capacities. The result was that by the time the Class 19D was withdrawn from service in the late 1980s, many had exchanged their Type MP1 or Type MR tenders for Type MX Torpedo tenders and vice versa. Type MX Torpedo tenders also ended up attached to Class 19B and Class 19C locomotives.^[1][14]

The Class 19D was the most numerous South African branch line locomotive and, at 235 built for the SAR, was only twenty less in number than the Class 15F mainline locomotive, the most numerous South African steam class. The Class 19D was very versatile and saw main- and branch line service all over South Africa with the exception of the Western Cape, where the Class 19C was used.^[3]

Tasks varied from mainline local and international passenger trains on the section between Warrenton and Mafeking en route between South Africa and Northern Rhodesia via Bechuanaland and Southern Rhodesia, to secondary and branch line duties and in later years as shunting engines. On occasion, South African Class 19D locomotives worked through from Mafikeng in South Africa via Botswana all the way to Bulawayo in Zimbabwe. SAR Class 19D locomotives were also hired out for shunting work to the Rhodesia Railways for use at Beit Bridge and to Mozambique for use at Lourenco Marques.^[3]

From c. 1972, the new Union Carriage & Wagon-built Blue Train was stabled at Pretoria. After Capital Park's blue-liveried Class S2 no. 3793 was withdrawn along with the rest of its class in 1979–1980, the Pretoria station carriage-shunt duties were taken over by a blue-painted Class 19D no. 2749, the only member of the class to serve in a different SAR livery from the usual black. Apart from shunting work, the blue Dolly was often specially requested to work the Cullinan train during the Jacaranda season.^[15]

The Class 19D served until right at the end of the South African steam era and were amongst the last steam locomotives to be replaced by electric and diesel-electric traction.^[3]

SAR Class 19D on the George - Knysna Line

The SAR Class 19D locomotive was a vital workhorse on the scenic George - Knysna (Outeniqua Choo Tjoe) line in South Africa. Known for its reliability, it handled both passenger and freight services efficiently.

Passenger Services: SAR Class 19D locomotives were commonly used for passenger trains, providing travelers with a comfortable journey through the Western Cape's picturesque landscapes.

Freight Transport: These locomotives played a crucial role in hauling timber from, showcasing their remarkable hauling capabilities.

Scenic Journeys: Tourists enjoyed breathtaking views of forests, hills, and the coast when traveling on trains pulled by SAR Class 19D locomotives.

Though the line is no longer operational, the SAR Class 19D's legacy in South African railway history endures.

Other operators

Other Southern African railways and some industries also purchased locomotives built to the Class 19D design. When these foreign versions are included, a total of 268 locomotives were built to the Class 19D design making them even more numerous than the Class 15F.^[3]

Industrial

As they were being retired, several Class 19D locomotives were sold into industrial service. By the late 1980s, some of them were already at work at Dunn's, Saiccor, Loraine Gold Mine and Bamangwato Concessions Ltd. (BCL) in Botswana, and more were to follow.^[3]

As late as 2011, two Class 19Ds which had been used on the Vaal Reefs Gold Mine in the 1980s until they were retired and dumped at Jan Kempdorp where they stood unprotected for about twenty years, were bought by BCL Selebi-Phikwe. The locomotives, possibly numbers 2678 and 2689, were to be overhauled for use by the mine there, which was still operating ex-SAR Class 19D and ex-RR 19th class locomotives. By June 2012, the first of these two was put into service. However the mine closed in late 2016 putting the entire fleet out of work and now up for sale (December 2018).^[20][21]