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South African Class 16E 4-6-2

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South African Railways
Company typeGovernment agency
IndustryRail transport
Headquarters
South Africa
ProductsLocomotives, rail services

South African Railways Class 16E 4-6-2 Steam Locomotive

The Class 16E 4-6-2 steam locomotives were introduced by South African Railways in 1935, designed specifically for express passenger service.

In that year, six units of the Class 16E, featuring a 4-6-2 wheel configuration, were commissioned to operate high-speed passenger trains. These locomotives were built to meet the demands of rapid transit on South Africa’s rail network.

Manufacturer

In the aftermath of the Great Depression in South Africa from 1930 to 1933, the South African Railways (SAR) aimed to enhance its express passenger service between Cape Town and Johannesburg. To achieve faster average speeds on its premier express trains, the Class 16E was developed under the guidance of A.G. Watson, who served as SAR's Chief Mechanical Engineer from 1929 until 1936. This class was designed specifically for deployment on the Union Express and Union Limited services. A total of six locomotives were constructed by Henschel and Son in Kassel, Germany, and were delivered in 1935, with numbers ranging from 854 to 859.

Characteristics

The Class 16E featured coupled wheels measuring 72 inches (1,830 millimetres) in diameter, making it one of the most outstanding Cape gauge express passenger locomotives ever produced. It boasted the largest fire grate area found on any Pacific-type engine outside North America. Its coupled wheels represented the largest diameter ever employed on a narrow-gauge locomotive, while its service weight and tractive effort matched or surpassed most Pacifics beyond North America.

File:A.G. Watson.jpg
A.G. Watson

Watson faced significant challenges in maintaining axle loads within the strict limits set by the Chief Civil Engineer. This led to the use of thinner materials than usual for components such as the ashpan, cab, and side running boards. Even the original number plates were manufactured from aluminium to reduce weight. Despite these measures, the axle load reached 20 long tons 19 hundredweight (21,290 kilograms), making it the heaviest axle load applied to any SAR locomotive or rolling stock at that period.

Introduced alongside the Class 15E Mountain type in 1935 was the Type JT tender, which featured a coal capacity of 14 long tons (14.2 tonnes), water storage of 6,000 imperial gallons (27,300 litres), and an axle load limited to 17 long tons 15 hundredweight (18,030 kilograms).

The main bar frames were precision machined from rolled steel plates, with each frame constructed as a single continuous piece from front to rear. Hollow crank pins were fitted to the wheels, while an oil bath center pivot was installed on the leading bogie. The connecting and coupling rods utilized floating bronze bushes and were crafted from a specialized chrome-nickel alloy steel featuring a fluted cross-section. To prevent derailment on sharp curves, the central set of driving wheels was flangeless with wider treads than the other two sets.

To compensate for the large coupled wheels and still deliver increased tractive effort, cylinders measuring 24 inches (610 millimetres) in bore and 28 inches (711 millimetres) in stroke were employed. Combined with a boiler pressure rated at 210 pounds per square inch (1,448 kilopascals), this configuration produced a tractive effort of 35,280 pounds-force (156.9 kilonewtons) at 75% boiler pressure. Each cylinder casting was integrated with half of the smokebox saddle, allowing interchangeability of parts.

File:Class 16E 858 (4-6-2) driver.jpg
Drive shafts operating poppet valve camshafts are similar to those used in many rear-wheel drive automobiles and trucks

Building upon the successful implementation of rotary cam poppet valves on the Class 19C, this valve gear was also incorporated into the Class 16E design. The valves were actuated by external rotary propshafts driven by mechanisms linked to the driving coupled wheels. Double-seated valves were positioned at both ends of each cylinder, resulting in short, straight ports between valves and cylinders. Admission valves measured 8 inches (203 millimetres) in diameter, while exhaust valves were slightly larger at 9 inches (229 millimetres). Many components of the rotary cam gear—including main drive and reversing mechanisms—were interchangeable with those used on the Class 19C. This poppet valve arrangement contributed to exceptionally smooth running characteristics.

The Class 16E was equipped with a Watson Standard no. 3A boiler, part of Watson's standardisation initiative involving various boiler types. Designed for a maximum operating pressure of 225 pounds per square inch (1,551 kilopascals), its barrel plates and firebox outer shell were constructed from nickel steel. Both boiler and firebox were fully insulated using Alfol material.

At a height of 9 feet 3 inches (2,820 millimetres) above rail level, this boiler had the highest pitch among SAR locomotives at that time. Due to clearance constraints imposed by loading gauge restrictions, it featured a domeless design with an inspection manhole located atop where a dome would conventionally be placed. Steam collection occurred via multiple small feeder pipes connected to two collector pipes positioned as high as possible above water level; these merged into a main steam pipe measuring 7 inches (178 millimetres) in diameter leading to both superheater header and multiple valve regulator located within the smokebox. Steam pipes extending from this header to each cylinder measured 6 inches (152 millimetres) in diameter. The boiler was fitted with two large "Pop" safety valves mounted forward of the firebox on opposite sides of the boiler at approximately an 80-degree angle apart.

File:SAR Class 16E 854 (4-6-2) & AG Watson.jpg
A.G. Watson pictured alongside his Class 16E locomotive circa 1935

The firebox incorporated a power-operated Ajax fire-door along with a sectional pin-hole grate equipped with power-driven shaking gear. To maintain axle load restrictions, its ashpan was fabricated from relatively thin anti-corrosive steel plates possessing special heat-resistant properties. The brick arch inside was supported by five arch tubes each measuring 3 inches (76 millimetres) in diameter. SAR standard flexible stays were used throughout the firebox construction; access to these stays was facilitated by fitting a Watson cab featuring a distinctive slanted front—a design that later became standard across SAR steam locomotive classes alongside Watson's standardized boilers. This cab was constructed entirely from lightweight steel welded throughout for durability and weight savings.

Service

Initially assigned to Kimberley, this class routinely operated notable trains such as the Union Express heading south to Beaufort West and the Union Limited traveling northbound to Johannesburg. Post-Second World War, the Union train evolved into the Blue Train. Although these locomotives were never based at Braamfontein Loco in Johannesburg, they received maintenance there when running services between Kimberley and Johannesburg.[1]

These engines demonstrated excellent performance, combining reliability with cost-efficiency when managing loads within their design limits. However, after the original wooden-bodied coaches of the Union trains were replaced in 1939 by heavier, steel-bodied air-conditioned carriages, the load capacity rose to 600 long tons (610 tonnes) or more. This increase rendered the Class 16E unsuitable for such duties, leading to their reassignment to Bloemfontein in the Orange Free State.[2][3][4]

From Bloemfontein, these locomotives hauled scheduled passenger services including the Orange Express, operating routes northwards toward Johannesburg and southwards to De Aar, as well as services extending to Kimberley. The introduction of air-conditioned lounge cars on trains like the Orange Express and Trans-Karoo further increased train weights, again surpassing the Class 16E’s capabilities. Consequently, these engines were phased out of service by 1972.[4]

Preservation

File:HGG-16E-857-Schild.jpg

Upon Watson’s retirement in 1936, locomotive no. 858 was officially named in his honor. It bore the inscription Allan G Watson above its number plates on each cab side. By the time the Class 16E was retired from active duty, this same engine carried the name Betty beneath its headlight.[1]

As of 2015, two units remained preserved in relatively good condition. Locomotive no. 858 Betty was kept outdoors at Beaconsfield in Kimberley, while no. 857 Ann Smith • Bloemfontein Queen was stored under cover at the Bloemfontein locomotive depot.[5]

Number Works no. THF / Private Leaselend / Owner Current Location
857 Hensc 22586 THF Transnet Heritage Foundation (Museum) Bloemfontein Locomotive Depot
858 Hensc 22587 THF Steamnet 2000 Kimberley Locomotive Depot

Commemoration

A set of four commemorative postage stamps issued by the South African Post Office on 27 April 1983 included a 20c stamp featuring a Class 16E locomotive. This series was created to honor South Africa’s steam locomotives, which were being rapidly phased out at that time. The stamp design and artwork were crafted by renowned stamp artist Hein Botha. The image depicted Class 16E no. 858. Additionally, a traditional SAR locomotive number plate outline served as a special cancellation mark for De Aar on the release date.[6]

Illustration

In their later service years, Class 16E locomotives were fitted with smoke deflectors.

References

  1. ↑ 1.0 1.1 Cite error: Invalid <ref> tag; no text was provided for refs named Soul of a Railway 7-2
  2. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named Holland 2
  3. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named SAR&H Aug 1946
  4. ↑ 4.0 4.1 Cite error: Invalid <ref> tag; no text was provided for refs named Paxton-Bourne
  5. ↑ Template:Middleton-SA Loco Guide
  6. ↑ Philatelic Bulletin 176, issued by Philatelic Services and INTERSAPA, 1983
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