South African Class MD 2-6-6-2

CSAR Mallet 2-6-6-2 Saturated
South African Class MD 2-6-6-2

CSAR no. 1001, SAR no. 1617, c. 1910

Type and origin
Power type	Steam
Designer	American Locomotive Company
Builder	American Locomotive Company
Serial number	46581
Model	CSAR Mallet
Build date	1910
Total produced	1

Specifications
Configuration:
• Whyte	2-6-6-2 (Prairie Mallet)
• UIC	(1'C)C1'nv4
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.	46 in (1,168 mm)
Trailing dia.	28 ¹⁄₂ in (724 mm)
Tender wheels	33 ¹⁄₂ in (851 mm)
Minimum curve	350 ft (107 m)
Wheelbase	65 ft 6 in (19,964 mm)
• Engine	40 ft 3 in (12,268 mm)
• Coupled	8 ft 4 in (2,540 mm) each
• Tender	17 ft 11 in (5,461 mm)
• Tender bogie	4 ft 7 in (1,397 mm)
Length:
• Over couplers	73 ft 7 ¹⁄₄ in (22,435 mm)
Height	12 ft 10 ³⁄₈ in (3,921 mm)
Frame type	Bar
Axle load	15 LT 0 cwt 2 qtr (15,270 kg)
• Leading	7 LT 14 cwt 3 qtr (7,862 kg)
• 1st coupled	14 LT 9 cwt 3 qtr (14,720 kg)
• 2nd coupled	14 LT 2 cwt 2 qtr (14,350 kg)
• 3rd coupled	13 LT 17 cwt 1 qtr (14,080 kg)
• 4th coupled	15 LT 0 cwt 2 qtr (15,270 kg)
• 5th coupled	14 LT 11 cwt 1 qtr (14,800 kg)
• 6th coupled	14 LT 10 cwt 3 qtr (14,770 kg)
• Trailing	6 LT 7 cwt 3 qtr (6,490 kg)
• Tender axle	14 LT 3 cwt 1 qtr (14,390 kg) av.
Adhesive weight	86 LT 12 cwt (87,990 kg)
Loco weight	100 LT 14 cwt 2 qtr (102,300 kg)
Tender weight	56 LT 14 cwt (57,610 kg)
Total weight	157 LT 8 cwt (159,900 kg)
Tender type	2-axle bogies
Fuel type	Coal
Fuel capacity	10 LT (10.2 t)
Water cap	5,000 imp gal (23,000 l)
Firebox type	Round-top
• Firegrate area	49.5 sq ft (4.60 m²)
Boiler:
• Pitch	7 ft 9 in (2,362 mm)
• Diameter	6 ft ¹⁄₈ in (1,832 mm)
• Tube plates	19 ft 10 ¹⁄₈ in (6,048 mm)
• Small tubes	271: 2 ¹⁄₄ in (57 mm)
Boiler pressure	200 psi (1,379 kPa)
Safety valve	Ramsbottom
Heating surface	3,325 sq ft (308.9 m²)
• Tubes	3,169 sq ft (294.4 m²)
• Firebox	156 sq ft (14.5 m²)
Cylinders	Four
High-pressure cylinder	18 in (457 mm) bore 26 in (660 mm) stroke
Low-pressure cylinder	28 ¹⁄₂ in (724 mm) bore 26 in (660 mm) stroke
Valve gear	Walschaerts
Valve type	HP Piston LP Richardson balanced slide
Valve travel	HP 5 in (127 mm) LP 5 ¹⁄₂ in (140 mm)
Valve lap	HP 1 in (25 mm) LP ⁷⁄₈ in (22 mm)
Couplers	Johnston link-and-pin

Performance figures
Tractive effort	45,900 lbf (204 kN) @ 50%

Career
Operators	Central South African Railways South African Railways
Class	Class MD
Number in class	1
Numbers	CSAR 1001, SAR 1617
Delivered	1910
First run	1910
Withdrawn	1926

The South African Railways Class MD 2-6-6-2 of 1910 was a steam locomotive from the pre-Union era in Transvaal.

In March 1910, the Central South African Railways commissioned a single experimental Mallet articulated compound steam locomotive with a 2-6-6-2 wheel arrangement. In 1912, when the locomotive was assimilated into the South African Railways, it was renumbered and designated Class MD.^[1]^[2]^[3]^[4]

Manufacturer

The first Mallet articulated compound steam locomotive on the Central South African Railways (CSAR) was ordered for test purposes from the American Locomotive Company in 1910. It was numbered 1001 and placed in service in March 1910. With its full working order weight of 157 long tons (160 tonnes), it was the heaviest locomotive in the world working on Cape gauge at the time.^[1]^[2]^[3]^[4]^[5]^[6]

Compound expansion

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. By comparison, in the more usual arrangement of simple expansion (simplex), steam is expanded just once in any one cylinder before being exhausted through the smokebox.^[1]^[7]

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.^[1]^[3]

Characteristics

The bar frames of the rear engine unit and its high-pressure cylinders were rigidly attached to the boiler with the engine’s wide firebox extending over the coupled wheels. The front engine unit and its low-pressure cylinders were not rigidly attached to the boiler barrel, but carried the boiler on a single sliding bearing which was placed between the leading and intermediate coupled wheels. The underside of the smokebox was flattened to provide clearance between it and the cylinder assemblies of the front engine unit. The two engine units were coupled together by a single vertical pin connection, arranged at a point on the centre-line of the high-pressure cylinder saddle casting. This arrangement gave the locomotive a short rigid wheelbase of 8 feet 4 inches (2,540 millimetres) which made it capable of traversing curves of short radius.^[2]

The locomotive used saturated steam. The high-pressure cylinders had piston valves arranged above the cylinders, while the low-pressure cylinders had Allen Richardson balanced slide valves, also arranged above the cylinders and all actuated by Walschaerts valve gear. Copper steam pipes were arranged on each side of the dome and passed vertically down outside the boiler to the steam chests of the high-pressure cylinders. The exhaust from the high-pressure cylinders passed through a receiver pipe along the centre of the engine to the low-pressure cylinders. The exhaust from the low-pressure cylinders passed to the smokebox and blast pipe through a pipe fitted with flexible connections.^[2]

The firebox had a short combustion chamber. The boiler barrel was telescopic and made up in three courses from ⁵⁄₈ inch (16 millimetres), ¹¹⁄₁₆ inch (17 millimetres) and ³⁄₄ inch (19 millimetres) thick plate respectively. The Walschaerts valve motion was operated by hand screw gear, with the reversing gear for one engine unit's set of gear arranged to be raised while the other's was lowered for forward or reverse, thereby balancing each other.^[2]

Performance

At low speed, the locomotive proved to be capable of handling heavier trains than any of the existing CSAR fleet of goods locomotives, but at higher speeds of 25 to 30 miles per hour (40 to 48 kilometres per hour) it could not compete successfully because of excessive wear on the moving parts which resulted in failures and as a consequence, high maintenance cost. Part of the problem arose from the fact that the Mallet was expected to run to the same train schedules as the non-articulated locomotive fleet in spite of the fact that its smaller coupled wheels made it more suited to heavy low-speed work. It has been surmised that, had it been superheated and equipped with larger diameter coupled wheels, the results may have been much better.^[1]^[2]^[6]

Service

The Mallet was acquired as an experiment, the ultimate object being to improve traffic flow on the 80 miles (129 kilometres) coal line between Witbank and Germiston. The increase of traffic and the resultant congestion on this line with a ruling gradient of 1 in 100 (1%) was causing considerable delays en route, which led to excessive hours of duty being imposed on crews. The intent was to determine the feasibility of replacing the existing Class 11 locomotives on this line with more powerful Mallets to be able to increase train loads from 900 to 1,600 long tons (914 to 1,626 tonnes).^[1]

South African Railways

Railway network of the Central South African Railways in 1910 upon the establishment of the Union of South Africa and the South African Railways

When the Union of South Africa was established on 31 May 1910, the three Colonial government railways (Cape Government Railways, Natal Government Railways and CSAR) were united under a single administration to control and administer the railways, ports and harbours of the Union. Although the South African Railways and Harbours came into existence in 1910, the actual classification and renumbering of all the rolling stock of the three constituent railways were only implemented with effect from 1 January 1912.^[8]

While the South African Railways (SAR) came into existence in 1910, the actual classification and renumbering of all the rolling stock of the three constituent railways required careful planning and was only implemented with effect from 1 January 1912.^[4]

In 1912, the engine was renumbered 1617 and designated the sole Class MD locomotive on the SAR. It remained in service on the line between Witbank and Germiston until it was withdrawn from service and scrapped in 1926.^[1]^[3]^[4]^[9]

Illustration

CSAR no. 1001, c. 1910

References

Wikimedia Commons has media related to South African Class MD 2-6-6-2.

1 2 3 4 5 6 7 Holland, D.F. (1971). Steam Locomotives of the South African Railways. 1: 1859–1910 (1st ed.). Newton Abbott, Devon: David & Charles. pp. 138–140. ISBN 978-0-7153-5382-0.
1 2 3 4 5 6 Espitalier, T.J.; Day, W.A.J. (1945). The Locomotive in South Africa - A Brief History of Railway Development. Chapter VI - Imperial Military Railways and C.S.A.R. (Continued). South African Railways and Harbours Magazine, March 1945. pp. 181-183.
1 2 3 4 Paxton, Leith; Bourne, David (1985). Locomotives of the South African Railways (1st ed.). Cape Town: Struik. p. 86. ISBN 0869772112.
1 2 3 4 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)
↑ "Powerful Freight and Passenger Locomotives for a Narrow Gauge Railway". American Engineer and Railroad Journal: 192–194. May 1910. Retrieved 31 December 2012.
1 2 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 1. (Accessed on 4 May 2017)
↑ Compounding Steam Engines
↑ The South African Railways - Historical Survey. Editor George Hart, Publisher Bill Hart, Sponsored by Dorbyl Ltd., Published c. 1978, p. 25.
↑ Holland, D. F. (1972). Steam Locomotives of the South African Railways. 2: 1910-1955 (1st ed.). Newton Abbott, Devon: David & Charles. p. 140. ISBN 978-0-7153-5427-8.

Locomotives of the Central South African Railways
3' 6" gauge	CSAR 0-6-0ST 1896 CSAR 4-6-0T 1887 CSAR Class 6-L1 CSAR Class 6-L2 CSAR Class 6-L3 CSAR Class 7 CSAR Class 8-L1 CSAR Class 8-L2 CSAR Class 8-L3 CSAR Class 9 CSAR Class 10 1904 CSAR Class 10 1910 CSAR Class 10-2 Saturated CSAR Class 10-2 Superheated CSAR Class 10-C CSAR Class 11 CSAR Class B 0-6-4T CSAR Class C 2-8-4T CSAR Class D CSAR Class E 4-8-0TT CSAR Class E 4-8-2T CSAR Class E 4-10-2T CSAR Class F CSAR Class M CSAR Mallet Saturated CSAR Mallet Stoker CSAR Mallet Superheated CSAR Rack 4-6-4RT CSAR Railmotor IMR 0-6-0ST 1896 IMR 4-6-0T 1887 IMR 46 Tonner 0-6-4T IMR 55 Tonner 2-6-4T IMR 7th Class 4-8-0 IMR 8th Class 4-8-0 IMR Reid Tenwheeler 4-10-2T IMR Western Australian 2-8-4T NZASM 10 Tonner NZASM 13 Tonner NZASM 14 Tonner NZASM 18 Tonner NZASM 19 Tonner NZASM 32 Tonner NZASM 40 Tonner NZASM 46 Tonner OVGS 1st Class 4-4-0TT OVGS 2nd Class 2-6-0 OVGS 2nd Class 2-6-0ST OVGS 3rd Class 4-4-0 OVGS 4th Class G 4-6-0 OVGS 5th Class K 4-6-0 1890 OVGS 5th Class K 4-6-0 1891 OVGS 6th Class L 4-6-0 OVGS 6th Class L2 4-6-0 OVGS 6th Class L3 4-6-0 PPR 0-4-0ST Natal PPR 26 Tonner PPR 35 Tonner Portuguese PPR 55 Tonner
2' gauge	CSAR Pankop
List of South African locomotive classes South African locomotive history

Locomotives of South Africa

Steam

7' ¼" gauge	East London 0-4-0VB Table Bay 0-4-0ST Table Bay 0-4-0T Table Bay 0-4-0WT
4' 8½" gauge	Cape 0-4-0T Blackie Cape 0-4-2 Cape 2-4-0T CGR 0-4-0ST Aid Natal 0-4-0ST Durban Natal 0-4-0WT Natal Natal 4-4-0T Perseverance
3' 6" gauge Tank engines	CGR 0-4-0ST 1873 CGR 0-4-0ST 1874 CGR 0-4-0ST 1881 CGR 0-4-0ST 1881 Coffee Pot CGR 0-6-0ST CGR 0-6-0T CGR 2-6-0ST 1900 CGR 2-6-0ST 1902 CGR 1st Class 0-4-0ST 1875 CGR 1st Class 0-4-0ST 1876 CGR 1st Class 2-6-0ST CGR 1st Class 4-4-0T CGR 2nd Class 4-4-0T CGR 3rd Class 2-6-0T CGR Railmotor CSAR Class C CSAR Class E CSAR Rack 4-6-4RT CSAR Railmotor Durban's Congella Durban's Edward Innes Durban's John Milne Durban's Sir Albert Port Elizabeth 0-4-0ST Kowie Railway 0-6-0T Kowie Railway 4-4-0T Metropolitan & Suburban 4-6-2T NGR 2-6-0T Durban & Pietermaritzburg NGR Class I 2-6-2T NGR Class K 0-4-0ST NGR Class K 0-6-0ST NGR Class K 2-6-0T NZASM 10 Tonner NZASM 13 Tonner NZASM 14 Tonner NZASM 18 Tonner NZASM 19 Tonner NZASM 32 Tonner NZASM 40 Tonner PPR 26 Tonner PPR 35 Tonner Portuguese SAR Class A SAR Class B SAR Class C SAR Class C1 SAR Class C2 SAR Class D SAR Class E SAR Class F SAR Class G SAR Class H SAR Class H1 SAR Class H2 SAR Class J SAR Class K SAR Railmotor SAR Dock 0-4-0ST SAR Dock 0-4-0T SWA 2-8-0T
3' 6" gauge Tender engines	CGR 1st Class 2-6-0 1876 BP CGR 1st Class 2-6-0 1876 Kitson CGR 1st Class 2-6-0 1879 CGR 1st Class 2-6-0 1891 CGR 1st Class 4-4-0 CGR 1st Class 4-4-0TT CGR 2nd Class 2-6-2TT CGR 3rd Class 4-4-0 1883 CGR 3rd Class 4-4-0 1884 CGR 3rd Class 4-4-0 1889 CGR 3rd Class 4-4-0 1898 CGR 3rd Class 4-4-0 1901 CGR 3rd Class 4-4-0 1903 CGR 4th Class 4-4-2 CGR 4th Class 4-6-0TT 1880 CGR 4th Class 4-6-0TT 1882 CGR 4th Class 4-6-0TT 1882 Joy CGR 4th Class 4-6-0TT 1884 CGR 5th Class 4-6-0 1890 CGR 5th Class 4-6-0 1891 NGR Havelock NGR Class I SAR Class Exp 1 SAR Class Exp 2 SAR Class Exp 3 SAR Class Exp 4 SAR Class Exp 5 SAR Class Exp 6 SAR Class S SAR Class S1 SAR Class S2 SAR Class 1 SAR Class 1A SAR Class 1B SAR Class 2 SAR Class 2C SAR Class 3 SAR Class 3A SAR Class 3B SAR Class 4 SAR Class 4A SAR Class 5 SAR Class 5A SAR Class 5B SAR Class 6 SAR Class 6A SAR Class 6B SAR Class 6C SAR Class 6D SAR Class 6E SAR Class 6F SAR Class 6G SAR Class 6H SAR Class 6J SAR Class 6K SAR Class 6L SAR Class 6Y SAR Class 6Z SAR Class 7 SAR Class 7A SAR Class 7B SAR Class 7C SAR Class 7D SAR Class 7E SAR Class 7F SAR Class 8 SAR Class 8A SAR Class 8B SAR Class 8C SAR Class 8D SAR Class 8E SAR Class 8F SAR Class 8R SAR Class 8X SAR Class 8Y SAR Class 8Z SAR Class 9 SAR Class 10 SAR Class 10A SAR Class 10B SAR Class 10C SAR Class 10D SAR Class 11 SAR Class 12 SAR Class 12A SAR Class 12B SAR Class 13 SAR Class 14 SAR Class 14A SAR Class 14B SAR Class 14C 1st SAR Class 14C 2nd SAR Class 14C 3rd SAR Class 14C 4th SAR Class 15 SAR Class 15A SAR Class 15B SAR Class 15C SAR Class 15CA SAR Class 15E SAR Class 15F SAR Class 16 SAR Class 16A SAR Class 16B SAR Class 16C SAR Class 16D SAR Class 16DA 1928 SAR Class 16DA 1930 SAR Class 16E SAR Class 17 SAR Class 18 SAR Class 19 SAR Class 19A SAR Class 19B SAR Class 19C SAR Class 19D SAR Class 20 SAR Class 21 SAR Class 23 SAR Class 24 SAR Class 25 SAR Class 25NC SAR Class 26 SAR Katanga SWA 2-8-0
3' 6" gauge Articulated engines	CGR Fairlie CGR Kitson-Meyer SAR Class FC SAR Class FD SAR Class GA SAR Class GB SAR Class GC SAR Class GCA SAR Class GD SAR Class GDA SAR Class GE SAR Class GEA SAR Class GF SAR Class GG SAR Class GH SAR Class GK SAR Class GL SAR Class GM SAR Class GMA SAR Class GO SAR Class HF SAR Class KM SAR Class MA SAR Class MB SAR Class MC SAR Class MC1 SAR Class MD SAR Class ME SAR Class MF SAR Class MG SAR Class MH SAR Class MJ SAR Class MJ1 SAR Class U
2' 6" gauge	Cape Copper John King & Miner Cape Copper Britannia Cape Copper Caledonia Cape Copper Clara Cape Copper Condenser Cape Copper Scotia Namaqua Copper Pioneer Walvis Bay 2-4-2T Hope
2' & 600mm gauges	ACR Class NG-G16A CGR NG 0-4-0T CGR NG 0-6-0T CGR NG 4-6-2T CGR Type A 2-6-4T CGR Type C 0-4-0T NGR Class N 4-6-2T SAR Dutton SAR NG 0-4-0T SAR Class NG1 SAR Class NG2 SAR Class NG3 SAR Class NG4 SAR Class NG5 SAR Class NG6 SAR Class NG7 SAR Class NG8 SAR Class NG9 SAR Class NG10 SAR Class NG-G11 SAR Class NG-G12 SAR Class NG-G13 SAR Class NG-G14 SAR Class NG15 SAR Class NG-G16 SWA Class Ha SWA Class Hb SWA Class Hc SWA Class Hd SWA Jung SWA Zwillinge

Electric

Amcoal Class E38

Gas-electric

SAR Gas-electric

Diesel

3' 6" gauge Diesel-electric	PRASA Class Afro 4000 SAR Class DS SAR Class DS1 SAR Class 31-000 SAR Class 32-000 SAR Class 32-200 SAR Class 33-000 SAR Class 33-200 SAR Class 33-400 SAR Class 34-000 SAR Class 34-200 SAR Class 34-400 SAR Class 34-500 SAR Class 34-600 SAR Class 34-800 SAR Class 34-900 SAR Class 35-000 SAR Class 35-200 SAR Class 35-400 SAR Class 35-600 TFR Class 35-800 SAR Class 36-000 SAR Class 36-200 SAR Class 37-000 Spoornet Class 39-000 TFR Class 39-200 TFR Class 43-000 TFR Class 44-000
2' gauge Diesel-electric	SAR Class 91-000
3' 6" gauge Diesel-hydraulic	SAR Class 61-000
3' 6" gauge Electro-diesel	Spoornet Class 38-000

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