Class MD (Locobase 13088)

Data from Holland (1972, I), p.140 and from "Powerful Freight and Passenger Locomotives for a Narrow Gauge Railway", American Engineering and Railroad Journal (May 1910), pp. 192-194. Works number was 46581 in 1910.

This was the CSAR's prototype Mallet, bought from Alco in the same year that North American company sold a smaller 2-6-6-0 to Natal Government (see Locobase 13087). CSAR's engine had a trailing truck that improved tracking.

Assigned to service between Witbank and Germiston, 1001 set a record for weight in Africa and on the 42" gauge worldwide. Holland's assessment grants that "...at low speeds it was a sound, capable locomotive and could handle heavier trains than any of the existing goods locomotives."

But the railway soon confirmed experience with low-drivered Mallets on other railroads around the world: They could not be run very fast as the wear on components increased cost and maintenance time. The MFs that followed (Locobase 11079) enhanced power through superheating, but retained the small drivers.

1001, renumbered 1617, was scrapped in 1926.

Class ME (Locobase 2938)

Data from Holland (1972,II), p. 21-22.

This was the first (and only) simple-expansion Mallet on the SAR.

Among the very first Mallets to be delivered with 4 simple-expansion cylinders, the ME's design also included a superheater. Clearly the goal was to pack as much power into a small freight-hauler that pressed lightly on the ground. Indeed, the rail weights on the branch lines for which this engine was intended didn't exceed 45 lb/yard (22.5 kg/metre). It appears from Holland's drawing to have had a Belpaire boiler.

He observes that the ME "was quite successful in operation and was only scrapped in 1937."

Class MF (Locobase 11079)

Data from Holland (1972, II) and from "Powerful Freight and Passenger Locomotives for a Narrow Gauge Railway", American Engineering and Railroad Journal (May 1910), pp. 192-194. Works numbers were 49115-46124 in 1910 and 50039-50043 in 1911.

Continuations of the Alco Mallet prototype MD supplied to the CSAR earlier in that year, but with superheating added. Piston valves supplied the HP cylinders, Allen-Richardson balanced slide valves served the LP cans. These operated in Witbank coal train service. Six (1620-1623, 1631-1632) were simpled in the mid-1920s; see Locobase 2937.

One engine, class MG, was delivered to an odd design which increased the diameter of the leading engine group's drivers to 51"; it was a flop. In addition, the mechanical stoker, while promising, was so noisy and complicated that it was soon replaced by hand-firing.

Class MF - superheated (Locobase 2937)

Data from Holland (1972, II); and "South African Class MF 2-6-6-2" in Wikipedia at [], last accessed 20 September 2021.

The Alco Mallets delivered to the CSAR in 1910-1911 (Locobase 11079) proved quite satisfactory - so much so that six of the class were superheated in the 1920s. According to Wikipedia, the conversion consisted of replacing the LP cylinders that used slide valves with simple-expansion cylinders supplied through piston valves.

Wikipedia reports that the 1620, 1631-1632 went to East London to answer the call for more power because trains leaving East London station immediately met a 2 1/2% grade, "making it an extremely difficult section." Unfortunately, the trio "appear to have not been up to the task in the Eastern Cape, however." The three had been idled by 1926 and all MFs were withdrawn by 1939.

Class MH (Locobase 2866)

Data from Holland, Volume II (1972), pp. 31-32. See also F C Coleman, "Mallet Compound Locomotives for the South African Railways", Railway Review, Volume 58, No 5 (5 February 1916), pp. 195-196; and M C Williams, "The Advantages of Articulated Locomotives", Railway Gazette, Volume 37, No 5 (4 August 1942), pp. 160-167.(Thanks to Alexander Blessing for his 12 July 2023 email supplying an alternate superheater area and correcting the adhesion wheelbase.) Works numbers were 20958-20962 in 1915.

Still-bigger Prairie Mallet articulated compound that like the MJ 2-6-6-0s (Locobase 2864) had outside bearings on the leading truck, and slide valves forward with piston valves supplying the rear cylinders. They used a round-topped boiler, however, that was originally set at 200 psi, but later reset to 180 psi (12.4 bar). These were main-line engines operating in the Transvaal that were rated at 500 tons up the 1.05% ruling grade up the Durban-Cato Ridge line.

Among the heaviest engines ever to run on a Cape Gauge railway, the MH class is generally regarded as "outstanding".But as satisfactory as a Mallet might have been, the MHs couldn't compare to the GA Beyer-Garratts in 1921 trials described in Locobase 745 and in greater detail in the M C Williams report cited above.