4-6-2 - Usage - South Africa - Cape Gauge

Cape Gauge

The first use of the 4-6-2 wheel arrangement in South Africa was in 1901, when the Natal Government Railways (NGR) rebuilt one of its Class K&S 4-6-0T tank locomotives to a 4-6-2T locomotive, in order to extend its range by providing a larger bunker. In 1912, when it was assimilated into the South African Railways (SAR), it was designated Class C1. In that same year four more of these locomotives were built from surplus material in the SAR’s Durban workshops.

No more tank locomotives with this wheel arrangement saw use on 3 ft 6 in (1,067 mm) Cape gauge in South Africa.

Three Class 5 and one experimental Karoo tender locomotive variants were introduced between 1903 and 1912.

• In 1903 the first two Karoo locomotives entered passenger service on the Cape Government Railways (CGR). It was a development of the CGR Class 6 2-6-2 and was designed by Chief Locomotive Superintendent H.M. Beatty. The locomotives, built by Kitson and Company, were acquired to cope with the increasing weight of passenger trains on the one in eighty ruling gradient between Beaufort West and De Aar in the Karoo, hence the Karoo Class name. In 1912, when they came onto the SAR roster, they were designated Class 5A.
• Following on the success of the first two Karoo Class locomotives, a further four were ordered from Beyer, Peacock and Company in 1904. They were modified slightly in view of the experience gained with the original two. On the SAR they were all designated Class 5B, until one was later reboilered with a Watson Standard no. 1 boiler and reclassified Class 5BR. All of them were later equipped with piston valve cylinders and superheaters.
• In 1907 the CGR placed a single experimental three cylinder compound Pacific in service, based on the second Karoo Class. Built by the North British Locomotive Company (NBL), it was not classified and was simply referred to as the "Three Cylinder Compound". The cylinders were arranged in the "Smith" system of compounding, with a single high pressure cylinder situated between the two low pressure cylinders. The locomotive had a bar frame, Walschaerts valve gear and used saturated steam. Compared to a simplex two-cylinder Karoo, the compound could take a heavy train up a long continuous grade at a much higher speed, while experienced drivers found it could outperform the Karoo in terms of power as well as fuel and water consumption. In 1912 the SAR classified it as Class Experimental 1.
• The Enlarged Karoo, built by Vulcan Foundry, was one of the locomotive types that were designed and ordered by the CGR before the SAR was established and that ended up being delivered to the newly established national railways of the Union of South Africa in 1912. It was a larger and heavier version of the Class 5B, with a higher pitched boiler, Belpaire firebox, larger diameter pilot and driving wheels and larger cylinders. The four locomotives were designated Class 5. One of them was later reboilered with a Watson Standard no. 1 boiler, equipped with a superheater and reclassified to Class 5R.

Five Class 9 Pacific passenger locomotives, designed by P.A. Hyde, the first Chief Locomotive Superintendent of the Central South African Railways (CSAR), were delivered from Vulcan Foundry in 1904. They had bar frames, Stephenson valve gear and used saturated steam, and proved very useful for passenger work with moderate loads, working the mail trains from Johannesburg to Durban as far as Charlestown on the Transvaal-Natal border for many years. On the SAR they retained their Class 9 classification.

Five Class 10 variants were introduced between 1904 and 1910.

• Also in 1904 and also designed by Hyde, fifteen Class 10 Pacific locomotives were delivered to the CSAR from NBL. The locomotives were of an extremely advanced design, superheated and with the highest boiler pitch yet in South Africa, with plate frames, wide Belpaire fireboxes, outside admission piston valves and Walschaerts valve gear. In 1912, when they were assimilated into the SAR, they retained their Class 10 classification.
• Ten heavy Pacific passenger locomotives, designed by CSAR Chief Mechanical Engineer (CME) G.G. Elliot based on Hyde’s Class 10 design, were ordered from NBL and delivered in 1910. They had plate frames, Belpaire fireboxes and Walschaerts valve gear and were delivered in two variants, five of them using saturated steam while the rest were superheated. While similar to the Class 10, their boilers were arranged further forwards, their firebox throats and back plates were sloped instead of being vertical, they used inside admission piston valves and their valve gear was reversed by means of a vertical steam reversing engine mounted on the right-hand running board. They were all classified as Class 10-2 by the CSAR, but in 1912 the SAR designated the saturated steam locomotives Class 10A and the superheated ones Class 10B. A further five superheated Class 10B locomotives were delivered to the SAR from Beyer, Peacock in 1912.
• Twelve light Pacific locomotives were also placed in service by the CSAR in 1910, classified as Class 10-C. Designed by Elliot and built by NBL, they were similar to the Class 10-2, but slightly smaller and with smaller driving wheels. They used saturated steam and had Belpaire fireboxes and Walschaerts valve gear, but they were soon reboilered and equipped with superheaters. In 1912 they were designated Class 10C by the SAR.
• One more Pacific was ordered by the CSAR from the American Locomotive Company (ALCO) in 1910. It was superheated and built to very much the same specifications as that of the Class 10-2 of that same year, but with a bar frame. It was slightly more powerful than the Class 10-2 and was designated Class 10 by the CSAR, along with the fifteen of 1904. In 1912 the locomotive became the sole Class 10D on the SAR.

Two Class 2 variants were introduced between 1905 and 1910.

• In 1905 two "Class Hendrie A" Pacific locomotives entered service on the NGR, designed by Locomotive Superintendent D.A. Hendrie and built by NBL. They had plate frames, used saturated steam and had Stephenson valve gear. To accommodate the wide and deep firebox, Hendrie used a bridle casting similar to that introduced on the CGR by Beatty with his Class 6 2-6-2 Prairie in 1903. This method of widening the frames for the firebox continued in South African locomotive design until 1927, when the general adoption of bar frames rendered it no longer necessary. In 1912 they were designated Class 2 on the SAR.
• In addition, two "Class Hendrie C" locomotives were built in the NGR’s Durban workshops in 1910. They were a redesigned version of the Hendrie A, similar in general proportions, but with Walschaerts valve gear, slightly larger diameter driving wheels, a larger boiler and a more enclosed cab that offered better protection to the crew. In 1912 the SAR designated them Class 2C.

Seven Class 16 variants were introduced between 1914 and 1935.

• The Class 16 Pacific was designed by Hendrie, CME of the SAR from 1910 to 1922, and was built by NBL, who delivered twelve locomotives in 1914. The design closely followed that of the Class 15 4-8-2 Mountain type that was introduced at the same time from the same builders, and many parts were made interchangeable. They had Walschaerts valve gear, were superheated and had Belpaire fireboxes. At the time it was considered a very large and powerful express locomotive, even when compared to British locomotives built to run on 4 ft 8 1⁄₂ in (1,435 mm) Standard gauge. With 60 inches (1,520 millimetres) driving wheels, the ratio of wheel diameter to rail gauge was the same as that of a Standard gauge locomotive having 81 inches (2,060 millimetres) driving wheels. Their tractive effort of 29,890 pounds-force (133.0 kilonewtons) at 75% boiler pressure exceeded the 27,800 pounds-force (123.7 kilonewtons) at 85% boiler pressure of Churchward’s The Great Bear on the Great Western Railway and equalled, also at 85% boiler pressure, that of Gresley’s subsequent Great Northern Pacifics. This made the Class 16 the most powerful express passenger locomotive design yet to have been built in Great Britain at the time.
• The Class 16A four-cylinder simplex Pacific of 1915 was designed by Hendrie and built by NBL. Two locomotives were delivered, identical in most respects to their predecessor Class 16 except that they had four cylinders instead of the usual two. All four cylinders were arranged in line below the smokebox and were the same size, with the outer cylinders driving the centre driving wheels while the inner cylinders operated on a cranked leading driving wheel axle. The result was a very smooth running locomotive capable of very fast running, but since the available space on a Cape gauge locomotive prevented larger cylinders from being fitted, the four-cylinder design was never repeated by the SAR.

• The Class 16B Pacific, also designed by Hendrie, was also built by NBL, who delivered ten locomotives in November 1917. They were identical to the predecessor Class 16 and successor Class 16C in most respects, except that they had wider cabs than the Class 16, while the Class 16C had a combustion chamber in the firebox. All ten were eventually reboilered with Watson Standard no 2B boilers and Watson cabs with slanted fronts, and reclassified to Class 16CR.
• Ten Class 16C locomotives, also designed by Hendrie and built by NBL, were delivered in 1919 with another twenty following in 1922. Identical to predecessors Class 16 and Class 16B in most respects except for the addition of a combustion chamber, they proved to be excellent free-steaming, fast and reliable locomotives with a reserve of power greater than either of the predecessors. All thirty were later reboilered with Watson Standard no 2B boilers and also reclassified to Class 16CR.

• Seven Class 16D Pacific locomotives were built for the SAR by Baldwin Locomotive Works in 1925 and 1926. The Class was designed for working the Union Limited and Union Express fast passenger trains, forerunners of the Blue Train, between Johannesburg and Cape Town. The builders conformed to SAR requirements, but also incorporated the latest American railway engineering practices and introduced several new features to the SAR, such as top feeds to the boiler, self-cleaning smokeboxes, Sellar’s drifting valves, grease lubrication and arch tubes to support the brick arch and improve circulation. It had a bar frame extending from the front buffer beam to the rear dragbox, while its size earned it the nickname "Big Bertha". In 1926 number 860 made locomotive history by hauling the Union Limited over the 956 miles (1,539 kilometres) from Johannesburg to Cape Town in 29 hours.
• When orders for more Pacific locomotives were placed in 1928, the Class 16D design was modified by the CME, Colonel F.R. Collins, who shortened the frame to end at the front of the firebox and added a bridle casting, which resulted in a wider frame below the firebox and cab and consequently more ashpan room. The twenty Class 16DA locomotives were built between 1928 and 1930, six by Hohenzollern Locomotive Works in 1928, eight by Baldwin in 1929 and six by Henschel in 1930. The Hohenzollern and Baldwin locomotives differed from the Class 16D only by virtue of its shortened frame. When A.G. Watson succeeded Collins as CME in 1929, he designed a boiler with a very wide firebox of the Wootten type, with a grate area of 60 square feet (5.574 square metres) in order to improve the steaming properties of these locomotives. The grate was 15 square feet (1.394 square metres) larger than that of the Hohenzollern and Baldwin locomotives and was installed on the final six locomotives by Henschel. The steaming ability of these six, known as the "Class 16DA Wide Firebox", was phenomenal and led to the adoption of wide fireboxes without combustion chambers as the standard on all subsequent SAR mainline locomotives.

• The Class 16E Pacific was designed by Watson and built by Henschel, who delivered six locomotives in 1935. With its 72 inches (1,830 millimetres) diameter driving wheels it was considered to be the most remarkable Cape gauge express passenger locomotive ever built. The driving wheels were the largest ever used on any less than 4 ft 8 1⁄₂ in (1,435 mm) Standard gauge locomotive, and it had an all-up weight and tractive effort equal to or exceeding that of most Pacifics outside North America. It used rotary cam poppet valve gear driven by outside rotary shafts, which resulted in extremely free-running characteristics. It also boasted the largest fire grate on any Pacific outside North America. The Class 16E had a Watson Standard no. 3A boiler and, at 9 feet 3 inches (2.819 metres) above rail level, its boiler centre-line was the highest-pitched on the SAR. This and the limitations of the loading gauge made it impossible to install a normal steam dome and its place was taken by an inspection man-hole. Steam was collected through numerous small feeder pipes fixed into two collector pipes, which were arranged as high as possible above the water surface. The collector pipes joined together to form a main steam pipe, 7 inches (178 millimetres) in diameter, which led to the superheater header and multiple valve regulator, situated in the smokebox.