Utente:Alessandro Crisafulli/South African Class 25NC 4-8-4

Le locomotive della Class 25NC sono state un gruppo di locomotive a vapore delle South African Railways entrate in servizio dal 1953 al 1955.

Il gruppo 25NC è la versione senza condensatore delle locomotive del gruppo 25 delle SAR, costituito da novanta unità entrate in servizio nello stesso tempo. Tra il 1973 e il 1980 ottantasette unità del gruppo 25 furono trasformate in macchine senza condensatore e reimmatricolate nel gruppo 25NC.

Costruzione

Il gruppo 25NC senza condensatore e il gruppo 25 con condensatore, aventi lo stesso rodiggio e le stesse misure fondamentali, furono progettate dalle SAR in collaborazione con la Henschel and Son di Kassel (Germany). Tra il 1953 e il 1955 undici locomotive del gruppo 25NC, numerate da 3401 a 3411, furono costruite dalla North British Locomotive Company (NBL) and thirty-nine, numbers 3412 to 3450, by Henschel.

Caratteristiche

Il gruppo 25NC ha una distribuzione Walschaerts e cuscinetti a rulli su tutte le sale, comprese quelle dei carrelli a tre sale del Tendertender, delle bielle motrici e accoppiate, come pure della testa a croce e dei perni dello stantuffo, mentre gli assili dei carrelli di guida e posteriore della macchina hanno boccole del tipo Cannon. I cilindri e le loro incastellature furono fusi in un solo pezzo, mentre i cilindri e i cassetti della distribuzione del vapore furono eseguiti con fodere di ferro. Anche il telaio del tender fu eseguito con una sola fusione d'acciaio. Il rodiggio montato interamente su cuscinetti a rulli permise di ridurre notevolmente la resistenza al moto della locomotiva.

Le novanta unità con condensatore del gruppo 25 furono costruite quali parte della stessa ordinazioni, una dalla Henschel e il ressto dalla NBL. Le parti dei condensatori da installare sulle macchine e i tender con condensatori furono progettati e brevettati dalla Henschel.

Le teste a croce, del tipo "Alligator", 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.

Teething troubles

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.

Service

The Class 25NC initially served on the unelectrified main lines from De Aar via Kimberley to Klerksdorp. Until the Welverdiend electrification was extended to Klerksdorp, they worked through to Welverdiend as well. 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 that 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 reclassification

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. 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 are therefore usually identifiable as original Class 25NCs.

In the process their Type CZ 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 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 CZ tenders with their long round topped water tanks. Locomotives with these rebuilt tenders were soon nicknamed "Worshond" (Sausage dog or Dachshund).

The Red Devil

Between 1979 and 1981 number 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 3450 was retained.

Gallery

The main picture shows no. 3410 at Sannaspos in the Free State on 4 July 1999.

NBL built no. 3411 relieving a Class 4E on a northbound train at Beaufort West, Cape Province, 26 June 1966

NBL built no. 3410 "Paula" making its way to the water tanks at Sprngfontein in the Free State, circa 1995

Henschel built no. 3422 "Bergrivier" with a Worshond tender working the Union Express, circa 2002

Henschel built no. 3440 being prepared to be hauled to Pretoria for restoration, Beaconsfield, Kimberley, 25 August 2007

Henschel built "Red Devil" no. 3450, shortly after being rebuilt to the only Class 26, Pretoria, 25 April 1981

Type EW1 tender with mechanical stoker, Beaconsfield, Kimberley, Northern Cape, 18 September 2009

Bibliografia

Fonti a stampa

• Richard Roosen, Class "25" condensing locomotives on the South African Railways. Design and operating experiences. Paper Nº 607, in Journal of the Institution Locomotive Engineers, vol. 50, n. 274, 1961, pp. 243–282.

Storiografia e complementi

• (EN) D. F. Holland, Steam Locomotives of the South African Railways, volume 2: 1910-1955, Newton Abbott, David & Charles, 1972, ISBN 0-71535-427-2., pp. 108–111.
• Luciano Greggio, Le locomotive a vapore. Modelli di tutto il Mondo dalle origini ad oggi con dati tecnici, Milano, Mondadori, 1977, ISBN., pp. 220, 252-253.
• (EN) Leith Paxton, David Bourne, Locomotives of the South African Railways, Città del Capo, Struik, 1985, ISBN 0869772112., pp. 78–79
• Diavolo blu, in I treni oggi, vol. 8, n. 67, 1987, pp. 29-31.
• (EN) A. E. Durrant, Twilight of South African Steam, Newton Abbott, David & Charles, 1989, ISBN 0-71538-638-7.
• (DE) Siegfried Kademann, Wolfgang Messerschmidt, Henschel Lokomotiven von 1848 bis zum Intercity, Solingen, Bechtermünz Verlag, 1995, ISBN 3-86047-121-X. pp. 131, 135
• Francesco Pozzato, I giganti a scartamento ridotto. Le locomotive Gruppo 25 e 25NC delle SAR-SAS, in Tutto treno, vol. 12, n. 119, 1999, pp. 15-19.
• (EN) John N. Middleton, Railways of Southern Africa Locomotive Guide - 2002 (as amended by Combined Amendment List 4, January 2009), Herts, Beyer-Garratt Publications, 2002, ISBN. (2^a edizione, dicembre 2002).

Voci correlate

• Locomotiva SAR 25
• Locomotiva SAR 26

[[Categoria:Sudafrica]]
[[Categoria:Locomotive a vapore]]
[[Categoria:Locomotive a vapore SAR|Locomotive a vapore SAR]]
[[Categoria:Locomotive a vapore di rodiggio 2-4-2|SAR 26]]

http://en.wikipedia.org/wiki/South_African_Class_25NC_4-8-4