South African Class 25 4-8-4
|South African Class 25 4-8-4
& South African Class 25NC 4-8-4
|Designer||South African Railways
Henschel and Son
|Builder||North British Locomotive Company
Henschel and Son 
3451: Henschel 28730 
3452-3540: NBL 27312-27400 
Boilers: Henschel 28770-28773 
Henschel 28730, 28780-28839 
NBL & SAR built unnumbered 
|Rebuilder||South African Railways|
|Number rebuilt||87 from Class 25 to Class 25NC|
|Gauge||3 ft 6 in (1,067 mm) Cape gauge|
|30 in (762 mm)|
|Driver diameter||60 in (1,520 mm)|
|30 in (762 mm)|
|Wheelbase||Total: 95 ft 1.0625 in (28.983 m)
6 ft 10 in (2.083 m) bogie
15 ft 9 in (4.801 m) coupled
5 ft 6 in (1.676 m) trailing
38 ft (11.582 m) total
10 ft (3.048 m) bogie
45 ft 10 in (13.970 m) total
|Length||107 ft 6.0625 in (32.768 m) total|
|Height||13 ft (3.962 m)|
|Axle load||19.3 long tons (19.6 t) on 3rd driver|
|Weight on drivers||76.9 long tons (78.1 t)|
|Locomotive weight||241,920 lb (109.7 t) empty
121.05 long tons (123.0 t) w/o
|Tender weight||158,339 lb (71.8 t) empty
118.9 long tons (120.8 t) w/o
|Locomotive and tender
|400,259 lb (181.6 t) empty
236.95 long tons (240.8 t) w/o
* 3 axle bogies
* Wheels 34 in (864 mm)
* Length approx 57 ft 6 in (17.526 m)
|Fuel capacity||19 long tons (19.3 t)|
|Water capacity||5,450 imp gal (24,800 l)|
|Boiler||6 ft 4.125 in (1.934 m) inside diameter
19 ft (5.791 m) inside length
9 ft 1.625 in (2.784 m) pitch
|Boiler pressure||225 psi (1,550 kPa)|
|Firegrate area||70 sq ft (6.503 m2)|
|158 tubes 2.5 in (63.5 mm) diameter
40 tubes 5.5 in (140 mm) diameter
3,059 sq ft (284.190 m2)
|– Flues||37 sq ft (3.437 m2)|
|– Firebox||294 sq ft (27.313 m2)|
|– Total||3,390 sq ft (314.941 m2)|
|Superheater area||630 sq ft (58.529 m2)|
|Cylinder size||24 in (610 mm) bore
28 in (711 mm) stroke
|Tractive effort||45,360 lbf (201.8 kN) at 75% boiler pressure |
|Operator(s)||South African Railways|
|Number in class||90|
Between 1953 and 1955 the South African Railways placed ninety Class 25 condensing steam locomotives with a 4-8-4 Northern wheel arrangement in service. The Class 25NC, placed in service at the same time, is the non-condensing version of the Class 25 condensing locomotive.
Because of the difficulties experienced in obtaining adequate supplies of suitable water in arid regions like the Great Karoo between Touws River and De Aar and from there into South West Africa (SWA), the South African Railways (SAR) began to give serious consideration to the possibility of introducing condensing locomotives as far back as the late 1930s. At one time it was considered to convert Class 12A 4-8-2 locomotives into condensing locomotives, but this never realised.
It was only after World War II that extensive condensing tests were carried out with the modified Class 20 2-10-2 locomotive. The approximately 90% water and 10% coal savings that were achieved in 1950 and 1951 during the tests with the Class 20 in the Transvaal, the Karoo and in SWA, led to the decision to proceed with the design of a new condensing locomotive.
The end result, the Class 25 4-8-4 condensing locomotive, can be considered as the ultimate in SAR non-articulated locomotive design. It was designed under the direction of L.C. Grubb, Chief Mechanical Engineer (CME) of the SAR from 1949 to 1954.
The design work on the locomotive’s condensing apparatus and the condensing tender was carried out by Henschel and Son, who built one locomotive complete with tender, number 3451, works number 28730. This locomotive was then dispatched to the North British Locomotive Company (NBL) in Glasgow, who built the rest of the Class 25 locomotives, numbered in the range from 3452 to 3540, as well as the first eleven Class 25NC non-condensing versions of the Class 25, numbered in the range from 3401 to 3411. They were delivered between 1953 and 1955.
Henschel built the other thirty-nine non-condensing locomotives, numbered in the range from 3412 to 3450, as well as sixty-one of the condensing tenders, to which they held the patent. The other twenty-nine condensing tenders were built by NBL. One more condensing tender was later built by the Salt River shops of the SAR on a spare frame that was delivered as part of the original order.
These tenders were large and complex enough that Henschel allocated separate builder’s or works numbers to them. At approximately 58 feet (18 metres) in length they were about 16 feet (4.9 metres) longer than their locomotives. One third of the total length of the tender was taken up by the water tank and coal bunker, while the rest was taken up by eight large radiators on each side, cooled by five steam driven roof mounted fans.
The condensing tenders were rather appropriately classified as Type CZ, since CZ is also the motor vehicle registration letters of Beaufort West, the capital town of the Karoo where the Class 25 was to serve.
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 drivers had Cannon-type axle boxes. The cylinders and frames were cast in one piece, while the steel cylinders and steam chests were fitted with cast iron liners. The tender frame was also a one piece steel casting. Since it was 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 coupling rods differed from the usual in the provision of three independent rods, thereby doing away with four knuckle joints and pins.
With the Class 25 condensing locomotive, spent steam was recycled and condensed back to water for repeated use. Since the steam wasn’t expelled up the chimney, the Class 25’s smokebox contained a steam turbine driven fan beneath the chimney in order to keep the draught going, with deflector plates to prevent char from causing excessive wear on the fan blades. Most of the char was collected at the bottom of the smokebox front, from where it was discharged through a steam ejector pipe that exhausted immediately in front of the chimney.
The draught turbine gave the locomotive its characteristic whining sound while running. On the Class 25 visual evidence of this altered smokebox is the locomotive’s banjo face, the distinctively shaped smokebox front. Spent steam was fed through the thick pipe on the locomotive’s left side back to the condensing tender, where five steam turbine driven fans in the roof blew air down through the radiators on each side of the tender.
The system proved to be extremely efficient and reduced water consumption by as much as 90% by using the same water up to eight times over, giving the Class 25 locomotive a range of 800 kilometres (500 miles) between water refills. In addition, the hot recycled feedwater resulted in a significantly reduced coal consumption.
Since spent steam was not expelled through the chimney, the condensers sounded unlike any other steam locomotive on South African rails. The non-condensing and free exhausting Class 25NC had the usual loud bark of a steam locomotive, especially under load, while the condensing Class 25 had more of a hoarse hollow chuff sound in addition to its turbine whine.
Soon after being placed in service, however, problems were experienced with connecting rods failing, 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, with the crossheads 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.
Considerable trouble was also experienced with the induced draught equipment. The blower blades suffered heavy edge wear and blade fractures occurred in both the blower and steam turbine wheels, which called for intense investigation by SAR engineers, Henschel representatives and the CSIR.
An initial attempt to solve the blade fracture problem by increasing the breadth of the blade roots from 7 to 14 millimetres (0.28 to 0.55 inches) was unsuccessful. Fatigue tests and stress analysis showed that both sizes of blades had failed due to fatigue at the sharp fillets as a result of the repeated changes in the centrifugal load due to variations in the turbine rotational speed. The solution was arrived at when it was realised that none of the single "lock" blades, which was supported by two conical pins, of any rotor had ever failed. When such conical pins were also introduced between all the other blades in the rotors, fatigue tests showed that this made them considerably stronger. The design was amended accordingly and the problem was solved. Some time later it was found that welding the blades onto the rotor edge proved to be a good cheaper alternative.
The Class 25 was built specifically for work in the Karoo and the Kalahari, where water is a scarce resource. They initially served on the unelectrified main line from Touws River via Beaufort West to De Aar, where they handled all goods and passenger traffic, including passenger trains like the Blue Train. When the section from Touws River to Beaufort West was electrified, the Class 25 continued working between Beaufort West and De Aar, but it now also worked between De Aar and Kimberley, across from Kimberley to Bloemfontein in the east, as well as westward from Kimberley to Postmasburg, Hotazel and Sishen in the Kalahari, hauling iron and manganese ore.
The Class 25 was a complex locomotive that required high maintenance, especially on the turbine blower fans in the smokebox, whose blades needed to be replaced frequently due to damage by solid particles in the exhaust. The equally complex condensing tender also required frequent maintenance. Between 1973 and 1980, after serving for twenty years and partially motivated by the spread of electric and diesel-electric traction over routes that were previously served exclusively by the Class 25, all but three of the Class 25 condensing locomotives, numbers 3451, 3511 and 3540, were converted to free exhausting and non-condensing locomotives as they went through the workshops for major overhauls. The converted locomotives were reclassified to Class 25NC.
The first conversion was done at De Aar on number 3452 and consisted of the turbine and exhaust pipe being removed from the smokebox and replaced with a blastpipe and chimney, while the tender was stripped of its condensing equipment, but retained its original fresh water and condensate tanks and feed pumps, with the radiator framing and roof paneled over. The locomotive’s general appearance therefore changed little, but while the conversion of 3452 was aesthetically superior when compared with subsequent conversions, it did not carry enough water.
The rest of the fleet was rebuilt at the Salt River shops in Cape Town. In the process their condensing tenders were also rebuilt to ordinary coal-and-water tenders by removing the condensing radiators and roof fans and replacing it with a massive round-top water tank. The shape and appearance of the tender conversion was dictated by strength considerations. It was considered to shorten the tender frame, but it was eventually retained as it was. The long cast steel frame of the tender was very flexible, but the radiator framing and roof contributed a great deal to the vertical stiffness. The final form of the tender tank supplied enough strength, with its semi-circular top welded to the original fresh water tank via the fan supports and the long triangular gussets set into the bunker sides that extended past the midpoint of the frame. To replicate the Class 25NC tender tank and bunker on the longer CZ tender frame would have exceeded the permissible axle loading by a considerable amount. Locomotives with these rebuilt tenders were soon nicknamed "Worshond" (the Afrikaans for Dachshund, literally translated as sausage dog).
When the Class 25 condensers were converted to Class 25NC non condensers, their number plates 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 plates. Locomotives with all four characters neatly in line and centred were therefore usually identifiable as original Class 25NCs. After they were relieved of their condensing gear, these locomotives served for another eleven years before being retired from the SAR when steam was finally completely replaced by electric and diesel-electric traction.
The main picture shows preserved number 3511 "Frieda" at Hartswater in the Cape Province on 24 April 1981.
- South African Class 20 2-10-2
- South African Class 25NC 4-8-4
- Tender locomotive numbering and classification
- The 4-8-4 "Northern"
- List of South African locomotive classes
- Holland, D.F. (1972). Steam Locomotives of the South African Railways, Volume 2: 1910-1955 (1st ed.). Newton Abbott, Devon: David & Charles. pp. 108–111. ISBN 978-0-7153-5427-8.
- Henschel & Son works list, compiled by Dietmar Stresow
- North British Locomotive Company works list, compiled by Austrian locomotive historian Bernhard Schmeiser
- Middleton, John N. (2002). Railways of Southern Africa Locomotive Guide - 2002 (as amended by Combined Amendment List 4, January 2009) (2nd, Dec 2002 ed.). Herts, England: Beyer-Garratt Publications. pp. 26–28.
- South African Railways and Harbours Locomotive Diagram Book, 2’0” & 3’6” Gauge Steam Locomotives, 15 August 1941, as amended
- Paxton, Leith; Bourne, David (1985). Locomotives of the South African Railways (1st ed.). Cape Town: Struik. pp. 10–11, 77–78. ISBN 0869772112.
- Condenser fitter Albie Bester’s reminiscences
- Steam in Action
- Steam in Action’s March 2009 newsletter, p15
- Information supplied by R.S. Loubser, son of M.M. Loubser
- Information supplied by R.S. Loubser concerning the Class 25
- Durrant, A E (1989). Twilight of South African Steam (1st ed.). Newton Abbott, London: David & Charles. pp. 107–109. ISBN 0715386387.
- SAR-L Group: Message #44177 by Phil Girdlestone on 10 November 2012
- Diamond Fields Advertiser, 27 March 1986
- Roosen, Dr.-Ing. R. (17 March 1960). "Class "25" Condensing Locomotives on the South African Railways — Design and Operating Experiences". J. Inst. Locomotive Engineers 50:2 (274): 243–280. Paper Nº 607.
|Class 25NC 3533, 5 October 2009 Rovos Rail's Class 25NC 3533, converted from a Class 25 condenser, enters Capital Park yard in the process of turning "The Pride of Africa" around on the Capital Park triangle. (1 minute)|