South African Class 61-000
No. D750, later no. 61-006, Kassel, Germany, c. 1958
The South African Railways Class 61-000 of 1959 was a diesel-hydraulic locomotive.
Between May and July 1959, the South African Railways placed seven Class 1-DH Henschel type DH-1420 diesel-hydraulic locomotives in service, to also gain experience with other forms of diesel motive power than diesel-electric. The locomotives were later reclassified to Class 61-000. In 1971, six of them were sold to Rhodesia Railways.
The Class 61-000 type DH-1420 diesel-hydraulic locomotive was designed and built for the South African Railways (SAR) by Henschel and Son in Kassel, Germany. Upon delivery, the locomotives were classified as Class 1-DH and numbered in the range from D745 to D751. When the SAR adopted a new classification and numbering system for electric- and diesel-powered locomotives c. 1960, they were reclassified as Class 61-000 and renumbered in the range from 61-001 to 61-007.
The Class 1-DH was acquired a year after the SAR had acquired its first diesel-electric locomotives to be built in quantity, the Class 1-DE, which had entered service in 1958 and which was later reclassified to Class 31-000. At the time, the SAR was still making extensive use of steam traction and limited use of electric traction. Its first diesel traction acquisitions were therefore the diesel-electric Class 1-DE and diesel-hydraulic Class 1-DH, to gain experience with both forms of diesel motive power.
The more commonly used diesel-electric locomotive makes use of a diesel engine prime mover to propel either a generator (DC) or an alternator (AC) to generate electric power, which is then used to propel axle-hung electric traction motors, one per powered axle, to drive the locomotive wheels. It therefore works on the same principle as a regular electric locomotive, the only difference being that it generates its own electric power instead of collecting it from an external supply such as overhead catenary or a third rail.
Diesel-hydraulic locomotives, on the other hand, use hydrokinetic transmission, also known as hydrodynamic transmission, in the form of torque converters to transmit power from prime mover to wheels.
The Class 61-000 was a centre-cab locomotive which was powered by two General Motors Electro-Motive Division (GM-EMD) type 6/567C V6 prime movers, each with a Voith type L306r triple-converter torque converter and each driving the wheels of one bogie. Power was transferred to the axles through drive shafts. Unlike diesel-electric locomotives, where each axle is driven by its own traction motor, individual wheel-slip was not possible on the Class 61-000, since each bogie's two axles were interconnected through the drive shafts.
The cab had two control stands and, since it was possible to start the six prime movers in three consisted locomotives from one engine cab, each control stand had six engine start buttons and six engine stop buttons. The electrical system was very complicated and unreliable, which eventually led to the locomotives being completely rewired in 1963.
South African Railways
The Class 61-000s spent their entire SAR working lives stationed at the Germiston diesel depot. One of them, no. 61-006, was involved in a head-on collision at Kaserne on 8 October 1966, and was eventually scrapped at the Koedoespoort workshops in Pretoria in September 1968. Problems with cracked axles resulted in the rest of the fleet being staged for repairs in 1967.
In 1971, the remaining six locomotives were sold to Rhodesia Railways (RR), later renamed the National Railways of Zimbabwe (NRZ), where they became the RR Class DH1 and were renumbered in the range from 3101 to 3106.
|RR & NRZ
- Paxton, Leith; Bourne, David (1985). Locomotives of the South African Railways (1st ed.). Cape Town: Struik. pp. 143–144. ISBN 0869772112.
- RR Class DH1 dimensional drawing
- South African Railways Index and Diagrams Electric and Diesel Locomotives, 610mm and 1065mm Gauges, Ref LXD 14/1/100/20, 28 January 1975, as amended
- Diesel-hydraulic locomotive
- 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. p. 78.
- Henschel-Lieferliste (Henschel & Son works list), compiled by Dietmar Stresow
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