South African Class 25 4-8-4


The South African Railways Class 25 4-8-4 of 1953 was a condensing steam locomotive.
Between 1953 and 1955, the South African Railways placed ninety condensing steam locomotives with a 4-8-4 Northern type wheel arrangement in service. The Class 25NC which was placed in service at the same time was a non-condensing version of the Class 25 condenser.

Background

Owing to the difficulties experienced to obtain adequate supplies of suitable water in arid regions like the Great Karoo between Touws River and Kimberley and from De Aar into South West Africa, the South African Railways 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 to condensing engines, but the idea was not put into practice.
Condensing locomotives were a rarity, but no novelty to South Africa, since the first condensing steam locomotives had already entered service in the Cape of Good Hope in the late nineteenth century. Between 1886 and 1888, three well-tank condensing locomotives with a wheel arrangement were placed in service by the Cape Copper Mining Company on its Namaqualand Railway, a gauge line between Port Nolloth and O'okiep.
On the SAR, it was only after World War II, that extensive condensing tests were carried out with the modified Class 20 locomotive. The approximately 90% water and 10% coal savings which were achieved during the tests with the Class 20 in the Eastern Transvaal and the Karoo in 1950 and 1951 led to the decision to proceed with the design of a new condensing locomotive.
The result, the Class 25 4-8-4 Northern type condensing loco­motive, can be considered as the ultimate in SAR non-articulated steam loco­motive design. It was designed under the direction of L.C. Grubb, Chief Mechanical Engineer of the SAR from 1949 to 1954.

Manufacturers

The design work on the locomotive's condensing apparatus and the condensing tender was carried out by Henschel & Son, who built one locomotive complete with tender, no. 3451 with works number 28730. After being trialled in Kassel, it was then dispatched to the North British Locomotive Company in Glasgow who built the rest of the Class 25 locomotives, numbered in the range from 3452 to 3540. They were delivered between 1953 and 1955.
Apart from the complete engine and tender no. 3451, Henschel built sixty more of the condensing tenders to which they held the patent, with works numbers in the range from 28780 to 28839, as well as four spare boilers for the Classes 25 and 25NC with works numbers in the range from 28770 to 28773. The last 29 condensing tenders were built by NBL.
In 1963, one more condensing tender, no. 3541, was built by the Salt River shops of the SAR on a spare cast frame which had been delivered as part of the original order which called for three spare frames, one for an engine and one each for a condenser and non-condenser tender.

Characteristics

The boiler was similar to the Watson Standard no. 3B boiler of the Class 15F, but with the distance between tubeplates reduced from to by the addition of a combustion chamber. While this resulted in a slight decrease in the total evaporative heating surface, there was a 40% increase in the firebox heating surface and a better ratio of firebox to grate area. The boiler was lagged with Cape Asbestos mattresses, manufactured and fitted in South Africa.
On the 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 to keep the draught going, with deflector plates that were supposed to prevent char from causing excessive wear on the fan blades.
The smokebox of the Class 25 was similar to that of the Class 25NC, but with the front extended to accommodate the centrifugal blower which was driven by an exhaust steam turbine mounted under the front of the smokebox. Apart from the usual round smokebox door in the centre of the smokebox front plate, the complete front smokebox plate on both classes was hinged to the wrapper plate on the right hand side of the smokebox in addition to being bolted to the angle ring at the smokebox front, to facilitate less cramped access to the blower equipment, superheater header and tubes.
The draught turbine gave the locomotive its characteristic whining sound while running. As delivered, the Class 25 had the usual round smokebox front, but this was later modified by adding a banjo-shaped extension to also cover the exhaust steam turbine. Spent steam was fed through a thick pipe on the engine's left hand side back to the condensing tender.
The banjo-shaped extension modification to the front of the smokebox was found necessary to cope with the copious amounts of char generated by brittle Witbank coal and mechanical stoking, since the original Henschel design proved to have too little capacity to keep accumulated char away from the exhaust turbine. Most of the char was collected in the trough of the banjo at the bottom of the smokebox front from where it was periodically ejected through a vertical steam ejector pipe inside the banjo door which exhausted immediately in front of the chimney.
In service, the turbine-induced draught of the Class 25 actually performed better than the regular draught of the Class 25NC. One advantage of the condenser was that while getting up steam, the blower could be opened at a boiler pressure of about to start the fan spinning, which drew the fire and accelerated getting up steam pressure. On a non-condensing locomotive the blower would be weak while steam pressure was still that low.
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 reversing link trunnion. Since the Class 25 was entirely mounted on roller bearings, very little effort was required to move these huge locomotives.
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. 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 the provision of three independent rods, thereby doing away with four knuckle joints and pins.
The locomotive was able to negotiate curves with a radius of, with gauge widening and superelevation. The wheels, axles and axleboxes of the leading bogie were designed to be interchangeable with those of the Class 15F, while the wheels and axles of the trailing bogie were interchangeable with those of the Class 24's trailing bogie.
The locomotive's brakes were operated by two diameter cylinders on the engine and four diameter cylinders on the tender. The brake riggings on the tender bogies were independent of each other and the front tender bogie was equipped with a hand brake. The engine and tender brake pipelines were fitted with delaying valves which delayed brake application on the locomotive until a predetermined degree of braking had been established throughout the train. A separate driver's brake valve permitted the continued application of locomotive brakes while the train brakes were being released or vacuum was being built up.
Almost one third of the total length of the Type CZ condensing tender was taken up by the coal bunker, which included the oil separator equipment to remove oil from spent steam and the mechanical stoker equipment which had a maximum delivery rate of of coal per hour. The rear two-thirds was taken up by eight large radiators on each side, cooled by five steam-driven roof-mounted fans. The water capacity consisted of two tanks, a fresh water tank in the centre of the tender between the radiators and a condensate tank under the tender belly between the bogies. Feedwater was taken directly from the condensate tank's hot contents rather than from the main tank's cold contents.
Since the temperature of the condensed feedwater was too high for the use of ordinary injectors, the boiler was fed by two turbo-pumps located under the cab. Each pump had a capacity of approximately per minute.
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 between water refills. In addition, the hot condensate feedwater resulted in a 7% reduction in coal consumption.

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. Since spent steam was not expelled through the chimney, the condensers sounded unlike any other steam locomotive on South African rails. Their non-condensing and free exhausting Class 25NC sister locomotives had the usual sharp 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.

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 South Africa's 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, a more sophisticated method of filtering out the cylinder and valve lubricant from the exhaust steam replaced the original centrifuge while the three independent coupling rods were replaced with the more conventional single coupling rod with knuckle joints.
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 25NC 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.
Considerable trouble was also experienced with the induced draught equipment. The blower blades suffered heavy edge wear from solid particles in the exhaust 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 was unsuccessful. Fatigue tests and stress analysis by the CSIR showed that both sizes of blades 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 were 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. Some time later it was found that welding the blades onto the rotor edge proved to be a good cheaper alternative. The design was eventually amended with the redesigned exhaust fan being manufactured from manganese steel and the problem was solved.

Service

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 mainline from Touws River via Beaufort West to De Aar where they handled all goods and passenger traffic, including top-line 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 to the east as well as westward from Kimberley to Postmasburg, Sishen and Hotazel in the Kalahari. From Postmasburg they worked iron and manganese ore to Bloemfontein, where relays of Free State power took over to Harrismith.

Rebuilding

The Class 25 was a complex locomotive which required high maintenance, especially on the turbine blower fans in the smokebox, the blades of which needed to be replaced frequently due to damage by solid particles in the exhaust. The equally complex condensing tender also needed frequent maintenance. Between 1973 and 1980, after serving for twenty years, and partially accelerated by the introduction of electric and diesel-electric traction over routes which were previously served exclusively by the Class 25, all but three of the 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.
It has been suggested that, had the Class 25 been modified to produce less black smoke or char as a result of incomplete combustion, in accordance with the Gas Producer Combustion System principles, which were applied by mechanical engineer David Wardale when he rebuilt a Class 25NC locomotive to the Class 26 Red Devil, the problem of char damage to the fan blades could have been largely eliminated. The GPCS program, however, only began near the end of the conversion of the Class 25s.
The first conversion was done at De Aar on no. 3452, and consisted of the turbine and exhaust pipe being removed from the smokebox and replaced with a blastpipe and chimney. 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 panelled over. The locomotive's general appearance therefore changed little, but while the conversion of no. 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 them with a massive round-topped water tank.
The shape and appearance of the tender conversion was dictated by strength considerations. Shortening the tender frame was considered, but it was eventually retained as it was. To replicate the Class 25NC tender tank and bunker on the longer Type CZ tender frame would have exceeded the permissible axle loading by a considerable amount. 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 rebuilt tender's 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 which extended past the midpoint of the frame. Locomotives with rebuilt tenders were soon nicknamed Worshond, Afrikaans for dachshund and literally translated as sausage dog. The worshond tenders were reclassified as Type EW2.
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 withdrawn from service by the SAR when steam was completely replaced by electric and diesel-electric traction.

Preservation

The following is a list of 25 class that have survived Converting to 25NC. Two are still owned by the Transnet Heritage Foundation. None are in service as of January 3rd 2019.
NumberWorks No.Transnet Heritage Foundation / PrivateLeaselend / OwnerCurrent LocationNotes
3451Hensc 28730Transnet Heritage FoundationSteamnet 2000Germiston Locomotive Depot
3511NBL 27371Transnet Heritage FoundationSteamnet 2000Kimberley Locomotive Depot
3540NBL 27400Scrapped between at Beaufort West

Works numbers

The locomotive numbers, builders, works numbers and tender builders are listed in the table. On the builders' works lists, all the locomotives are shown as having been built in 1953. The tenders were numbered in the range from 3451 to 3540 for their engines while the additional spare tender which was built at Salt River in 1963 was numbered 3541. All tenders bore the same works number as the engines they were built with, except the sixty tenders which were built by Henschel for engines which were built by NBL. These sixty were allocated Henschel works numbers.
Loco no.BuilderWorks no.Tender builderTender Works no.
3451Henschel28730Henschel
3452NBL27312Henschel28780
3453NBL27313Henschel28781
3454NBL27314Henschel28782
3455NBL27315Henschel28783
3456NBL27316Henschel28784
3457NBL27317Henschel28785
3458NBL27318Henschel28786
3459NBL27319Henschel28787
3460NBL27320Henschel28788
3461NBL27321Henschel28789
3462NBL27322Henschel28790
3463NBL27323Henschel28791
3464NBL27324Henschel28792
3465NBL27325Henschel28793
3466NBL27326Henschel28794
3467NBL27327Henschel28795
3468NBL27328Henschel28796
3469NBL27329Henschel28797
3470NBL27330Henschel28798
3471NBL27331Henschel28799
3472NBL27332Henschel28800
3473NBL27333Henschel28801
3474NBL27334Henschel28802
3475NBL27335Henschel28803
3476NBL27336Henschel28804
3477NBL27337Henschel28805
3478NBL27338Henschel28806
3479NBL27339Henschel28807
3480NBL27340Henschel28808
3481NBL27341Henschel28809
3482NBL27342Henschel28810
3483NBL27343Henschel28811
3484NBL27344Henschel28812
3485NBL27345Henschel28813
3486NBL27346Henschel28814
3487NBL27347Henschel28815
3488NBL27348Henschel28816
3489NBL27349Henschel28817
3490NBL27350Henschel28818
3491NBL27351Henschel28819
3492NBL27352Henschel28820
3493NBL27353Henschel28821
3494NBL27354Henschel28822
3495NBL27355Henschel28823
3496NBL27356Henschel28824
3497NBL27357Henschel28825
3498NBL27358Henschel28826
3499NBL27359Henschel28827
3500NBL27360Henschel28828
3501NBL27361Henschel28829
3502NBL27362Henschel28830
3503NBL27363Henschel28831
3504NBL27364Henschel28832
3505NBL27365Henschel28833
3506NBL27366Henschel28834
3507NBL27367Henschel28835
3508NBL27368Henschel28836
3509NBL27369Henschel28837
3510NBL27370Henschel28838
3511NBL27371Henschel28839
3512NBL27372NBL
3513NBL27373NBL
3514NBL27374NBL
3515NBL27375NBL
3516NBL27376NBL
3517NBL27377NBL
3518NBL27378NBL
3519NBL27379NBL
3520NBL27380NBL
3521NBL27381NBL
3522NBL27382NBL
3523NBL27383NBL
3524NBL27384NBL
3525NBL27385NBL
3526NBL27386NBL
3527NBL27387NBL
3528NBL27388NBL
3529NBL27389NBL
3530NBL27390NBL
3531NBL27391NBL
3532NBL27392NBL
3533NBL27393NBL
3534NBL27394NBL
3535NBL27395NBL
3536NBL27396NBL
3537NBL27397NBL
3538NBL27398NBL
3539NBL27399NBL
3540NBL27400NBL
SAR3541

Illustration