South African Class MC 2-6-6-0

Specifications
Specifications
Configuration:;
• Whyte	2-6-6-0 (Denver)
• UIC	(1'C)Cnv4 as built; (1'C)Chv4 (no. 1612 & 1615)
Driver	3rd & 6th coupled axles
Gauge	3 ft 6 in (1,067 mm) Cape gauge
Leading dia.	28+1⁄2 in (724 mm)
Coupled dia.	45+1⁄2 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+3⁄4 in (20,364 mm)
Height	12 ft 5+3⁄16 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
• Grate 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+3⁄4 in (4,947 mm)
• Small tubes	258: 2+1⁄4 in (57 mm)
Boiler pressure	200 psi (1,379 kPa)
Safety valve	Ramsbottom
Heating surface:
• Firebox	154 sq ft (14.3 m2)
• Tubes	2,462 sq ft (228.7 m2)
• Total surface	2,616 sq ft (243.0 m2)
Cylinders	Four
High-pressure cylinder	17+1⁄2 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
Valve type	HP Piston, LP Slide
Couplers	Johnston link-and-pin

Type and origin
Type and origin
Power type	Steam
Designer	North British Locomotive Company
Builder	North British Locomotive Company
Serial number	19577-19586
Model	NGR Mallet
Build date	1912
Total produced	10

South African Class MC 2-6-6-0
South African Class MC 2-6-6-0
	SAR Class MC no. 1608, c. 1912
Power type
Type and origin
Power type	Steam
Designer	North British Locomotive Company
Builder	North British Locomotive Company
Serial number	19577-19586
Model	NGR Mallet
Build date	1912
Total produced	10
Configuration:;
Specifications
Configuration:;
• Whyte	2-6-6-0 (Denver)
• UIC	(1'C)Cnv4 as built; (1'C)Chv4 (no. 1612 & 1615)
Driver	3rd & 6th coupled axles
Gauge	3 ft 6 in (1,067 mm) Cape gauge
Leading dia.	28+1⁄2 in (724 mm)
Coupled dia.	45+1⁄2 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+3⁄4 in (20,364 mm)
Height	12 ft 5+3⁄16 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
• Grate 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+3⁄4 in (4,947 mm)
• Small tubes	258: 2+1⁄4 in (57 mm)
Boiler pressure	200 psi (1,379 kPa)
Safety valve	Ramsbottom
Heating surface:
• Firebox	154 sq ft (14.3 m2)
• Tubes	2,462 sq ft (228.7 m2)
• Total surface	2,616 sq ft (243.0 m2)
Cylinders	Four
High-pressure cylinder	17+1⁄2 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
Valve type	HP Piston, LP Slide
Couplers	Johnston link-and-pin
Tractive effort
Performance figures
Tractive effort	44,810 lbf (199.3 kN) @ 50%
Operators
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

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. The high-pressure cylinders of the hind engine unit were equipped with piston valves while the low-pressure cylinders of the front engine unit were equipped with slide valves.^[1]

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). The locomotives 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 with 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-Germiston line. They were withdrawn from service during 1933.^[1]^[2]^[3]^[7]

References

^ ^a ^b ^c ^d ^e ^f ^g Holland, D. F. (1972). Steam Locomotives of the South African Railways. Vol. 2: 1910-1955 (1st ed.). Newton Abbott, England: David & Charles. pp. 21–22. ISBN 978-0-7153-5427-8.
^ ^a ^b ^c ^d ^e 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.
^ ^a ^b ^c ^d ^e ^f Paxton, Leith; Bourne, David (1985). Locomotives of the South African Railways (1st ed.). Cape Town: Struik. p. 85. ISBN 0869772112.
^ ^a ^b 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)
^ North British Locomotive Company works list, compiled by Austrian locomotive historian Bernhard Schmeiser
^ Compounding Steam Engines
^ Soul of A Railway, System 7, Western Transvaal, based in Johannesburg, Part 21: Witbank Line by Les Pivnic, Eugene Armer, Peter Stow and Peter Micenko. Caption 3. (Accessed on 4 May 2017)