South African Class 18 2-10-2
| Company type | Steam locomotive class |
|---|---|
| Industry | Rail transport |
| Founded | 1927 |
| Founder | Colonel F.R. Collins, DSO (designer) |
| Headquarters | South Africa |
| Products | Steam locomotives |
| Parent | South African Railways |
Overview
The South African Railways Class 18 2-10-2 steam locomotive was introduced in 1927.
During December 1927 and January 1928, the South African Railways commissioned two Class 18 locomotives, each equipped with three cylinders and featuring a 2-10-2 wheel configuration, commonly known as the Santa Fe type. These engines were assigned to operate on the coal transport route between Witbank and Germiston.
Manufacturer
The Class 18 2-10-2 Santa Fe type steam locomotive was conceived by Colonel F.R. Collins, DSO, who served as Chief Mechanical Engineer (CME) of the South African Railways (SAR) from 1922 to 1929. Manufactured by Henschel and Son in Germany, two units were supplied in 1927 and 1928, bearing the numbers 1360 and 1361.
Characteristics
These locomotives were robust three-cylinder machines. During that era, three-cylinder designs were increasingly common in Europe and the United States due to their smoother torque delivery, enhanced balance, and more effective crank-pin thrust distribution. However, this configuration also introduced greater mechanical complexity and resulted in elevated maintenance expenses.
Initially, the third cylinder was exposed beneath the smokebox but was later concealed by added plating. Representing the most powerful non-articulated steam locomotives to operate on the SAR, they produced a tractive effort of 53,650 pounds-force (239 kilonewtons) at 75% boiler pressure and could pull loads up to 1,800 long tons (1,829 tonnes) on the Witbank-Apex section’s 1% gradient.
Henschel’s contemporary marketing dubbed them the "Henschel Giants." In comparison with the Deutsche Reichsbahn’s Standard gauge Class 44 three-cylinder 2-10-0 locomotives, these units were generally larger. Although both had nearly identical overall weights, the Class 18’s shorter axles and frame stretchers—necessitated by its Cape gauge track—allowed weight savings that were redirected into components such as an enlarged firebox, making it the physically bigger locomotive.
The Class 18 featured a round-topped firebox equipped with a combustion chamber and arch tubes supporting a brick arch. It utilized a Duplex D.4 mechanical stoker powered by a four-cylinder steam engine mounted on its Type HT tender, which held 14 long tons (14.2 tonnes) of coal and 6,000 imperial gallons (27,300 litres) of water, with a maximum axle load of 19 long tons 8 hundredweight (19,710 kilograms).
To enable navigation through curves with a radius as tight as 320 feet (98 metres), despite its extended coupled wheelbase, the third and fourth driving wheelsets were designed without flanges. Additionally, it employed a Krauss-Helmholtz bogie arrangement: the leading driving wheels had limited lateral movement linked to a leading bissel bogie. The bissel bogie connected via a sleeve around the first driving axle so that any displacement of the bogie would be counteracted by an opposite movement of the leading driving axle, effectively guiding the wheels through curves.
The outside cylinders powered the third driving axle, while the inside cylinder drove the second axle through a cranked axle arrangement, with the cylinder mounted at an inclined angle. The three cranks were spaced at 120 degrees apart to accommodate this inclination of the inner cylinder.
Service
The Class 18 locomotives were introduced to address challenges posed by the growing weight of coal trains operating between Witbank and Germiston. At that time, the Class MF Mallet locomotives were deemed too slow, while the hauling capabilities of the non-articulated engines were being pushed to their limits.
However, these locomotives failed to meet expectations during their operational life. Despite featuring two sets of flangeless coupled wheels and employing the Krauss-Helmholtz system, the Class 18 suffered from significant flange and tyre wear. Additionally, the Chief Civil Engineer reported increased rail deterioration. The cylinder design was outdated, and combined with the lightweight motion components and rods, this resulted in locomotives that were costly and demanding in maintenance. The intricate valve gear lacked durability and frequently malfunctioned due to wear and breakage. Consequently, these engines required servicing after fewer than 40,000 miles (64,374 kilometres).
Both units of the Class 18 were retired by 1951. Following their withdrawal, the two Type HT tenders had their mechanical stokers removed and their drawgear altered to be compatible with Class 15CA locomotives. Subsequently, these tenders were reclassified as Type KT.
Knuckle couplers
Starting in 1927, the SAR initiated a transition from the longstanding Johnston link-and-pin coupling system—used since the Cape Government Railways inception in 1873—to AAR knuckle couplers on its Cape Gauge rolling stock. Evidence from period photographs, as well as official SAR Locomotive Diagram Books and Holland’s published dimensional drawings (mostly reflecting original, unmodified locomotives), indicates that Class 18 locomotives were delivered equipped with knuckle couplers. This was also true for other classes introduced in 1927, such as the GCA, GF, HF, and U.
The full conversion of all rolling stock took several years, with both coupling types remaining visible on equipment well into the late 1950s. During this interim phase, locomotive knuckle couplers featured a horizontal slot and a vertical hole within the knuckle itself to accommodate a link and pin respectively. This design allowed them to connect with vehicles still fitted with the older Johnston couplers.
Knuckle couplers had first appeared in South Africa more than twenty years prior. The Central South African Railways (CSAR) adopted Gould knuckle couplers on its Limited Express and Imperial Mail passenger trains in 1904. The Limited Express operated between Pretoria and Johannesburg, while the Imperial Mail ran between Pretoria and Cape Town. These early knuckle couplers also incorporated split knuckles to enable coupling with existing Johnston link-and-pin systems since CSAR retained those older couplers on all their locomotives to maintain compatibility with their own freight and older passenger stock as well as equipment from connecting railways.
Illustration
-
Class 18 displaying the third cylinder as originally built, circa 1930 -
Class 18 featuring plating below the smokebox concealing the third cylinder -
Cutaway illustration of a Class 18 2-10-2 steam locomotive -
.jpg)
.jpg)
References
Template:Locomotives of South Africa Template:Steam locomotive tenders