South African Class MC 2-6-6-0

South African Class MC 2-6-6-0

SAR Class MC no. 1608, c. 1912
Type and origin
Power type Steam
Designer American Locomotive Company
Builder North British Locomotive Company
Serial number 19577-19586
Model NGR Mallet
Build date 1912
Total produced 10
Specifications
Configuration 2-6-6-0 (Denver)
Driver 3rd & 6th coupled axles
Gauge 3 ft 6 in (1,067 mm) Cape gauge
Leading dia. 28 12 in (724 mm)
Coupled dia. 45 12 in (1,156 mm)
Tender wheels 30 in (762 mm)
Wheelbase 59 ft 3 in (18,059 mm)
  Engine 33 ft 5 in (10,185 mm)
  Coupled 8 ft 4 in (2,540 mm) per unit
  Tender 16 ft 6 in (5,029 mm)
  Tender bogie 4 ft 6 in (1,372 mm)
Length:
  Over couplers 66 ft 9 34 in (20,364 mm)
Height 12 ft 5 316 in (3,789 mm)
Axle load 14 LT 13 cwt (14,890 kg)
  Leading 8 LT 15 cwt (8,890 kg)
  1st coupled 14 LT 5 cwt (14,480 kg)
  2nd coupled 14 LT 5 cwt (14,480 kg)
  3rd coupled 14 LT 7 cwt (14,580 kg)
  4th coupled 14 LT 10 cwt (14,730 kg)
  5th coupled 14 LT 11 cwt (14,780 kg)
  6th coupled 14 LT 13 cwt (14,890 kg)
  Tender bogie Bogie 1: 21 LT 14 cwt (22,050 kg)
Bogie 2: 21 LT 16 cwt (22,150 kg)
  Tender axle 10 LT 18 cwt (11,070 kg)
Adhesive weight 86 LT 11 cwt (87,940 kg)
Loco weight 95 LT 6 cwt (96,830 kg)
Tender weight 43 LT 10 cwt (44,200 kg)
Total weight 138 LT 16 cwt (141,000 kg)
Tender type TM (2-axle bogies)
Fuel type Coal
Fuel capacity 8 LT 5 cwt (8.4 t)
Water cap 4,000 imp gal (18,200 l)
Firebox type Round-top
  Firegrate area 42.5 sq ft (3.95 m2)
Boiler:
  Pitch 7 ft 6 in (2,286 mm)
  Diameter 5 ft 8 in (1,727 mm)
  Tube plates 16 ft 2 34 in (4,947 mm)
  Small tubes 258: 2 14 in (57 mm)
Boiler pressure 200 psi (1,379 kPa)
Safety valve Ramsbottom
Heating surface 2,616 sq ft (243.0 m2)
  Tubes 2,462 sq ft (228.7 m2)
  Firebox 154 sq ft (14.3 m2)
Cylinders Four
High-pressure cylinder 17 12 in (444 mm) bore
26 in (660 mm) stroke
Low-pressure cylinder 28 in (711 mm) bore
26 in (660 mm) stroke
Valve gear Walschaerts
Couplers Bell link-and-pin
Performance figures
Tractive effort 44,810 lbf (199.3 kN) @ 50%
Career
Operators South African Railways
Class Class MC
Number in class 10
Numbers 1607-1616
Delivered 1912
First run 1912
Withdrawn 1933

The South African Railways Class MC 2-6-6-0 of 1912 was a steam locomotive.

In 1912, the South African Railways placed ten Class MC Mallet articulated compound steam locomotives with a 2-6-6-0 wheel arrangement in service in Natal.[1][2][3][4]

Manufacturer

In order to augment the Mallet locomotive fleet operating across the more difficult sections of the Natal mainline, the South African Railways (SAR) placed an order with the North British Locomotive Company for ten compound steam locomotives which were very similar to the Class MB. They were delivered and placed in service in May 1912, designated Class MC and numbered in the range from 1607 to 1616.[1][2][3][4][5]

Compounding

In a compound locomotive, steam is expanded in phases. After being expanded in a high-pressure cylinder and having then lost pressure and given up part of its heat, it is exhausted into a larger-volume low-pressure cylinder for secondary expansion, after which it is exhausted through the smokebox.[6]

In the compound Mallet locomotive, the rear set of coupled wheels are driven by the smaller high-pressure cylinders, which are fed steam from the steam dome. Their spent steam is then fed to the larger low-pressure cylinders, which drive the front set of coupled wheels. By comparison, in the more usual arrangement of simple expansion, steam is expanded just once in any one cylinder before being exhausted through the smokebox.[1][3]

Characteristics

Like the previous Mallets, these ten compound locomotives had Walschaerts valve gear and used saturated steam. Their Type TM tenders were the same as those of the Classes 3 and 3B, with a coal capacity of 8 long tons 5 hundredweight (8.4 tonnes) and a water capacity of 4,000 imperial gallons (18,200 litres), but they differed little from the previous Mallets in size, power and performance and may for all intents and purposes also have been classified as Class MB. It would seem that, compared to the Cape Government Railways, which tended to group locomotives in the same Class which were dissimilar even to the extent of having different wheel arrangements, the early SAR at times took locomotive classification to the other extreme.[1][3]

Unlike the Class MB, on which the sandboxes were placed on top of the boiler in accordance with American practice, the sandboxes of the Class MC were arranged on a different system, the advantages of which were questionable. The sandboxes for the hind engine unit were secured to the running board, just to the rear of the high-pressure cylinders, while those for the front engine unit were placed on the upper sides of the boiler, just to the rear of the smokebox.[2]

Superheating

The Class MC were satisfactory locomotives, but, like the earlier Mallet compounds, they would have performed better if they had been superheated. Two of them, numbers 1612 and 1615, were later equipped with new boilers and superheaters and their coupled wheels were retyred to a diameter of 46 inches (1,168 millimetres). No others were modified in this manner.[1][2][3]

Service

The Class MC joined the Class MA and MB fleet on the Natal mainline, working heavy coal trains between Estcourt and Highlands. In later years, some were transferred to the Cape Western System, where they served into the 1930s as banking locomotives up the Hex River Railpass between De Doorns and Touws River. Others were transferred to the Witwatersrand for general service and to haul coal on the Witbank line. They were withdrawn from service during 1933.[1][2][3]

References

  1. 1 2 3 4 5 6 Holland, D.F. (1972). Steam Locomotives of the South African Railways, Volume 2: 1910-1955 (1st ed.). Newton Abbott, Devon: David & Charles. pp. 21–22. ISBN 978-0-7153-5427-8.
  2. 1 2 3 4 5 Espitalier, T.J.; Day, W.A.J. (1945). The Locomotive in South Africa - A Brief History of Railway Development. Chapter VII - South African Railways (Continued). South African Railways and Harbours Magazine, May 1945. pp. 347-350, 356.
  3. 1 2 3 4 5 6 Paxton, Leith; Bourne, David (1985). Locomotives of the South African Railways (1st ed.). Cape Town: Struik. p. 85. ISBN 0869772112.
  4. 1 2 Classification of S.A.R. Engines with Renumbering Lists, issued by the Chief Mechanical Engineer’s Office, Pretoria, January 1912, pp. 9, 12, 15, 46 (Reprinted in April 1987 by SATS Museum, R.3125-6/9/11-1000)
  5. North British Locomotive Company works list, compiled by Austrian locomotive historian Bernhard Schmeiser
  6. Compounding Steam Engines
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