South African Class 25NC 4-8-4

South African Class 25NC 4-8-4
3410 at Sannaspos Free State in July 1999
Type and origin ♠ Type EW1 tender – ♥ Type EW2 tender Power type Steam Designer South African Railways (LC Grubb) Builder Henschel & Son North British Locomotive Company Serial number Henschel 28731-28769 NBL 27287-27296, 27311 Model Class 25NC Build date 1953 Total produced 137
Specifications Configuration: ​  • Whyte 4-8-4 (Northern) Driver 2nd coupled axle Gauge 3 ft 6 in (1,067 mm) Cape gauge Leading dia. 30 in (762 mm) Coupled dia. 60 in (1,524 mm) Trailing dia. 30 in (762 mm) Tender wheels 34 in (864 mm) Minimum curve 275 ft (84 m) Wheelbase ♠ 81 ft 4+11⁄16 in (24,808 mm) ♥ 95 ft 1+11⁄16 in (28,999 mm) ​  • Engine 38 ft (11,582 mm)  • Leading 6 ft 10 in (2,083 mm)  • Coupled 15 ft 9 in (4,801 mm)  • Trailing 5 ft 6 in (1,676 mm)  • Tender ♠ 32 ft (9,754 mm) ♥ 45 ft 10 in (13,970 mm)  • Tender bogie 10 ft (3,048 mm) Length: ​  • Over couplers ♠ 91 ft 6+9⁄16 in (27,903 mm) ♥ 107 ft 6+1⁄16 in (32,768 mm) Height 13 ft (3,962 mm) Frame type Cast Axle load 18 LT 14 cwt (19,000 kg) ​  • Leading 21 LT 2 cwt (21,440 kg)  • 1st coupled 18 LT 10 cwt (18,800 kg)  • 2nd coupled 18 LT 14 cwt (19,000 kg)  • 3rd coupled 18 LT 12 cwt (18,900 kg)  • 4th coupled 18 LT 9 cwt (18,750 kg)  • Trailing 22 LT 12 cwt (22,960 kg)  • Tender bogie Bogie 1: ♠ 51 LT 6 cwt (52,120 kg) Bogie 2: ♠ 54 LT 5 cwt (55,120 kg)  • Tender axle ♠ 18 LT 1 cwt 2 qtr (18,370 kg) Adhesive weight 74 LT 5 cwt (75,440 kg) Loco weight 117 LT 9 cwt (119,300 kg) Tender weight ♠ 105 LT 11 cwt (107,200 kg) Total weight ♠ 223 LT (226,600 kg) Tender type EW1 (3-axle bogies) EW2 (3-axle bogies) Fuel type Coal Fuel capacity ♠ 18 LT (18.3 t) ♥ 19 LT (19.3 t) Water cap. ♠ 10,500 imp gal (47,700 L) ♥ 11,200 imp gal (50,900 L) Firebox: ​  • Type Round-top  • Grate area 70 sq ft (6.5 m2) Boiler: ​  • Type Domeless  • Pitch 9 ft 1+5⁄8 in (2,784 mm)  • Diameter 6 ft 4+1⁄8 in (1,934 mm)  • Tube plates 19 ft (5,791 mm)  • Small tubes 158: 2+1⁄2 in (64 mm)  • Large tubes 40: 5+1⁄2 in (140 mm) Boiler pressure 225 psi (1,551 kPa) Safety valve Ross-pop Heating surface: ​  • Firebox 294 sq ft (27.3 m2)  • Tubes 3,059 sq ft (284.2 m2)  • Arch tubes 37 sq ft (3.4 m2)  • Total surface 3,390 sq ft (315 m2) Superheater: ​  • Type Melesco  • Heating area 630 sq ft (59 m2) Cylinders Two Cylinder size 24 in × 28 in (610 mm × 711 mm) bore x stroke Valve gear Walschaerts Valve type Piston Valve travel 7+3⁄8 in (187 mm) Loco brake Vacuum Couplers AAR knuckle
Performance figures Tractive effort 45,360 lbf (201.8 kN) @ 75%
Career Operators South African Railways Class Class 25NC Number in class 50 original, 87 rebuilt Class 25 Numbers 3401-3450, 3452-3510, 3512-3539 Delivered 1953-1954 First run 1953

The South African Railways Class 25NC 4-8-4 of 1953 was a class of steam locomotives built between 1953 and 1955 for the South African Railways (SAR). The Class 25NC was the non-condensing version of the Class 25 condensing locomotive, of which ninety were placed in service at the same time. Between 1973 and 1980, all but three of the condensing locomotives were converted to non-condensing and also designated Class 25NC.^[1][2]

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 LC Grubb, Chief Mechanical Engineer of the SAR from 1949 to 1954, in conjunction with Henschel & Son of Kassel in Germany who designed the condensing apparatus and the condensing tender of the Class 25 sister locomotive.^[3] Between 1953 and 1955,eleven Class 25NC locomotives were built by the North British Locomotive Company (NBL) and numbered in the range from 3401 to 3411 while 39 locomotives were built by Henschel and numbered in the range from 3412 to 3450.^[4][5][6]

The Class 25NC was superheated and used piston valves actuated by Walschaerts valve gear. Timken 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. Compared to earlier SAR practice, a novelty was the adoption of mechanical lubrication. A sixteen-feed lubricator was driven off the expansion link trunnion. The cylinders and frames were cast in one piece by Commonwealth Steel Company in the United States. 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.^{[1][7][8][9][10]}

The Alligator type crossheads 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.^[1]

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; 6,240 US gallons) per hour.^[7]

The locomotive was equipped with a Type EW1 tender which was equipped with a mechanical stoker of which the engine was mounted on the tender. The tank had a water capacity of 10,500 imperial gallons (47,700 litres; 12,600 US gallons) and the coal bunker a capacity of 18 long tons (18.3 tonnes; 20.2 short tons). 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.^[1][11]

Soon after entering 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, 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.^[1][12][10]

When new, the tapered Timken crankpin roller bearings soon became notorious for throwing their lubricant onto the underside of the boiler, from where it ran down to the lowest point and dripped onto the coupled wheel tyres along the way. This manufacturer's fault also applied to the Class 25 and was one of the reasons for the reputation of both classes of being slippery. Timken managed to resolve the problem before all their bearings had been replaced, but by then about two-thirds of the locomotives had already been fitted with redesigned coupling rods with SKF crankpin ball bearings.^[10]

The Class 25NC initially served on the unelectrified mainlines from De Aar via Kimberley to Welverdiend. They were pooled from their introduction and were run through from De Aar to Welverdiend and vice versa, recoaling at Warrenton. After electrification was extended from Welverdiend to Klerksdorp, they ran from there to De Aar, still recoaling at Warrenton. Later they also worked from Kimberley via Bloemfontein to Harrismith in the Free State while some joined the Class 25 condensers on the line from De Aar via Beaufort West to Touws River.^[4][13]

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 Mafeking.^[14]

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 were designed and patented by Henschel.^[1]

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.^[2][15]

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 water-bottom 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).^[14]

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, 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.^{[16][17][18][19]}

This was achieved by the use of a Gas Producer Combustion System, 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.^[16][17]

The following is a list of 25NC and 26 class that have survived into preservation.

Most are still owned by the Transnet Heritage Foundation. None except the class 25Nc 3437 & 25Nc 3482 (and it only for the winter months) are mainline certified as of 1 January 2019.

During 1988 a severe motive power shortage was experienced by the National Railways of Zimbabwe and discussions with South Africa revealed that numerous class 25NC 4-8-4, had been recently withdrawn from service and were available for either hire or purchase. NRZ decided to investigate the purchase of 20 to 25 of these locomotives for a short-term basis. A team of three were sent down from Bulawayo inspected 50 locomotives at Warrenton and De Aar.

A list of 28 locomotives was submitted from which it would be possible to choose 20 to 25, or any lesser number which might be needed

Category A (locomotives with 5 or more years before heavy overhaul)

3404, 3410, 3422, 3428, 3438, 3442, 3445, 3453, 3457, 3459, 3479, 3504, 3508, 3519

Category B (needing heavy repairs by 1993–1994)

3412, 3424, 3464, 3473, 3475, 3490, 3498, 3507, 3518, 3520, 3537

Category C (needing heavy repairs by 1992)

3439, 3446, 3515

The project did not materialise but several did survive into preservation.

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 sixty tenders were allocated Henschel works numbers.^{[1][11][25][26]}

>

• 
  NBL-built no. 3411 relieving electric units on a northbound Trans-Karoo at Beaufort West, Cape Province, 26 June 1966
• 
  NBL-built no. 3410 Paula making its way to the water tanks at Springfontein in the Free State, c. 1995
• 
  Preparing Henschel-built no. 3440 to be hauled to Pretoria for restoration by Rovos Rail, Beaconsfield, 25 August 2007
• 
  Henschel-built no. 3422 Bergrivier, converted to oil-firing, with two type X-20 water tenders on the Union Express, c. 2002
• 
  SAR-rebuilt Red Devil no. 3450, shortly after being rebuilt to the only Class 26, Pretoria, 25 April 1981

External videos

South African Steam: Trans Karoo Steam Finale: 2nd Last Run – March 1997 A short video featuring the second last run of steam on the Trans Karoo Express on 15 March 1997. The locomotives are Class 25NC no. 3422, a regular on the Trans Karoo, and Class 25NC no. 3407, a relatively rare engine on this train. The other two regular locomotives, nos. 3404 and 3476, were not available as they were being spruced up for the final run the following week. (Time 4:36)

External videos
Class 25NC 3533, 5 October 2009 Rovos Rail's Class 25NC 3533, converted from a Class 25 condenser, enters Capital Park yard on 5 October 2009, in the process of turning The Pride of Africa around on the Capital Park triangle. (Time 1:00)

Wikimedia Commons has media related to South African Class 25NC 4-8-4.