South African Class 25NC 4 8 4

Manufacturers

The Class 25NC non-condensing and Class 25 condensing 4-8-4 Northern type steam locomotives were designed by the South African Railways (SAR) under the direction of L.C. Grubb, Chief Mechanical Engineer of the SAR from 1949 to 1954, in conjunction with Henschel and Son of Kassel in Germany, who designed the condensing apparatus and the condensing tender of the Class 25 sister locomotive. Between 1953 and 1955, eleven Class 25NC locomotives, numbered in the range from 3401 to 3411, were built by the North British Locomotive Company (NBL), while 39 locomotives, numbered in the range from 3412 to 3450, were built by Henschel.

Characteristics

The Class 25NC was superheated and used piston valves, actuated by Walschaerts valve gear. Roller bearings were used throughout, including on the three-axle tender bogies, the coupling and connecting rods as well as the crosshead gudgeon pins, while the locomotive's leading bogies and coupled wheels had Cannon-type axle boxes. The cylinders and frames were cast in one piece by Commonwealth Steel Castings Corporation in the United States of America. The tender frame was also a one-piece steel casting and was a water-bottom frame, with the frame itself forming the bottom of the tank, instead of being a separate tank and frame as in previous designs. The steel cylinders and steam chests were fitted with cast iron liners. Being entirely mounted on roller bearings, very little effort was required to move these locomotives.

The crossheads, of the Alligator type, were split on the vertical centre line and clamped on to the end of the piston rods, which had three coned rings engaging in grooves in the crossheads. The original coupling rods differed from the usual in being three separate rods, thereby doing away with four knuckle joints and pins.

The multiple-valve superheater header was of the Melesco type. The boiler was fitted with four Ross Pop safety valves, each 2 ¹⁄₂ inches (64 millimetres) in diameter, and two Hopkinson boiler blowdown cocks on the firebox wrapper, one on each side. Feedwater was delivered to the boiler by two Friedmann vertical type non-lifting injectors, each with a capacity of 5,200 imperial gallons (23,600 litres) per hour.

Teething troubles

Soon after being placed in service, problems were experienced with failing connecting rods, big end bearings breaking up as well as cracks developing in the motion girder of the Alligator crossheads. After investigations by SAR engineers, with assistance from the South African Council for Scientific and Industrial Research (CSIR), the crossheads, slide bars and coupling rods were modified. The crossheads were converted to the multiple-bearing type with single guide bars, while the three independent coupling rods were replaced with the more conventional single coupling rod with knuckle joints.

Service

The Class 25NC initially served on the unelectrified mainlines from De Aar via Kimberley to Klerksdorp. They initially worked through to Welverdiend as well, until electrification was extended from Welverdiend to Klerksdorp. In later years, they also worked from Kimberley via Bloemfontein to Harrismith in the Free State, and some joined the Class 25 condensers on the line from De Aar via Beaufort West to Touws River.

When the line south from De Aar was dieselised between 1973 and 1974, the Class 25 condensers working there were moved north to work the section from De Aar to Kimberley, where they replaced twenty-two Class 25NCs, which were then relocated to Bethlehem in the Free State. From 1982, Class 25NCs also replaced Class 19Ds and Class GMAM Garratts on the line from Warrenton via Vryburg to Mafikeng.

Class 25 rebuilding

Along with the Class 25NC, ninety Class 25 condensing locomotives were built as part of the same order, one by Henschel and the rest by NBL. The condensing apparatus for these engines and their condensing tenders was designed and patented by Henschel.

Between 1973 and 1980, all but three of the ninety Class 25 condensers were converted to non-condensing locomotives and reclassified to Class 25NC, the exceptions being numbers 3451, 3511 and 3540. The number plates of some were copied and recast with the additional "NC" for "non-condensing" squeezed in next to the existing "25", which resulted in a lopsided class indication on their cabside plates. Locomotives with all four characters neatly in line and centred were therefore usually identifiable as original Class 25NCs.

In the process, their Type CZ condensing tenders were also rebuilt to ordinary coal-and-water Type EW2 tenders by removing the condensing radiators and roof fans and replacing it with a massive water tank. Since the Type CZ tenders were built on single cast steel main frames, it was impractical to attempt to shorten them, which resulted in the rebuilt Type EW2 tenders with their long round topped water tanks. Locomotives with these rebuilt tenders were soon nicknamed Worshond (Sausage dog or Dachshund).

The Class 26 Red Devil

Between 1979 and 1981, no. 3450, the last Class 25NC to be built, was rebuilt to the sole Class 26, the Red Devil, at the SAR workshops at Salt River in Cape Town. The primary objectives of the project were to improve the combustion and steaming rate, to reduce the emission of wasteful black smoke and to overcome the problem of clinkering.

This was achieved by the use of a Gas Producer Combustion System (GPCS), which relies on the gasification of coal on a low temperature firebed so that the gases are then fully burnt above the firebed. These extensive modifications justified reclassification and the locomotive became the first and only Class 26, although the locomotive's original Class 25NC number was retained.

Works numbers

The locomotive numbers, builders and works numbers are listed in the table. On the builders' works lists, all the locomotives are shown as having been built in 1953. All tenders bore the same works number as the engines they were built with, except the sixty tenders which were built by Henschel for condensing engines which were built by NBL. These 60 tenders were allocated Henschel works numbers as shown.