South African Class MB 2-6-6-0

NGR Mallet 2-6-6-0 1910
South African Class MB 2-6-6-0

NGR Mallet no. 337, SAR Class MB no. 1602, c. 1910

Type and origin
Power type	Steam
Designer	American Locomotive Company
Builder	American Locomotive Company
Serial number	48337-48341
Model	NGR Mallet
Build date	1910
Total produced	5

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 ¹⁄₂ in (724 mm)
Coupled dia.	45 ¹⁄₂ in (1,156 mm)
Tender wheels	30 in (762 mm)
Wheelbase	60 ft 9 ¹⁄₄ in (18,523 mm)
• Engine	33 ft 2 in (10,109 mm)
• Coupled	8 ft 4 in (2,540 mm) per unit
• Tender	17 ft 10 in (5,436 mm)
• Tender bogie	5 ft 10 in (1,778 mm)
Length:
• Over couplers	69 ft 1 in (21,057 mm)
Height	12 ft 5 ³⁄₁₆ in (3,789 mm)
Frame type	Bar
Axle load	16 LT 14 cwt (16,970 kg)
• Leading	7 LT 15 cwt (7,874 kg)
• 1st coupled	15 LT 5 cwt (15,490 kg)
• 2nd coupled	14 LT 10 cwt (14,730 kg)
• 3rd coupled	12 LT 9 cwt (12,650 kg)
• 4th coupled	11 LT 10 cwt (11,680 kg)
• 5th coupled	11 LT 16 cwt (11,990 kg)
• 6th coupled	16 LT 14 cwt (16,970 kg)
• Tender axle	11 LT 5 cwt (11,430 kg) average
Adhesive weight	82 LT 4 cwt (83,520 kg)
Loco weight	89 LT 19 cwt (91,390 kg)
Tender weight	45 LT (45,720 kg)
Total weight	134 LT 19 cwt (137,100 kg)
Tender type	2-axle bogies
Fuel type	Coal
Fuel capacity	10 LT (10.2 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 7 ¹⁄₂ in (5,067 mm)
• Small tubes	260: 2 ¹⁄₄ in (57 mm)
Boiler pressure	200 psi (1,379 kPa)
Safety valve	Ramsbottom
Heating surface	2,700.8 sq ft (250.91 m²)
• Tubes	2,546.2 sq ft (236.55 m²)
• Firebox	154.6 sq ft (14.36 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
Couplers	Bell link-and-pin

Performance figures
Tractive effort	44,810 lbf (199 kN) @ 50%

Career
Operators	Natal Government Railways South African Railways
Class	NGR Mallet SAR Class MB
Number in class	5
Numbers	NGR 337-341 SAR 1602-1606
Delivered	1910
First run	1910
Withdrawn	1924

The South African Railways Class MB 2-6-6-0 of 1910 was a steam locomotive from the pre-Union era in the Natal Colony.

In November 1910, the Natal Government Railways placed five 2-6-6-0 Mallet articulated compound steam locomotives in service. In 1912, when they were assimilated into the South African Railways, they were renumbered and designated Class MB.^[1]^[2]^[3]^[4]

Manufacturer

Following on the satisfactory performance of the experimental Mallet compound steam locomotive which had been acquired by the Natal Government Railways (NGR) in 1909, a further five similar locomotives were ordered from the American Locomotive Company (ALCO) in 1910. They were delivered in November of that year and numbered in the range from 337 to 341.^[1]^[2]^[4]

Characteristics

Like the previous Mallet locomotive, these five had Walschaerts valve gear, bar frames and used saturated steam. They differed little from the previous Mallet, basically only in respect of their larger boilers, which made them slightly heavier, and their tenders with a 1 long ton 10 hundredweight (1.5 tonnes) larger coal capacity.^[1]^[2]^[4]

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.^[5]

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]^[4]

Service

These five locomotives joined the first Mallet in banking service, working heavy coal trains between Estcourt and Highlands on the Natal mainline. To relieve coupler strain, they were used in three-locomotive trains and, in this manner, were able to haul 750 long tons (762 tonnes) up the one in thirty (3⅓%) gradients on that line.^[1]^[4]

South African Railways

Railway network of the Natal Government 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, NGR and Central South African Railways) 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, with Sir William Hoy appointed as its first General Manager, 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.^[3]^[6]

In 1912, these five locomotives were renumbered in the range from 1602 to 1606 and designated Class MB on the South African Railways. They had a relatively short service life and were withdrawn from service by 1924. Their early demise was probably brought forward considerably by the appearance of the Garratt locomotive type in 1921.^[1]^[3]^[4]

References

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. 13–14. ISBN 978-0-7153-5427-8.
1 2 3 Espitalier, T.J.; Day, W.A.J. (1945). The Locomotive in South Africa - A Brief History of Railway Development. Chapter VII - South African Railways. South African Railways and Harbours Magazine, April 1945. p. 274.
1 2 3 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)
1 2 3 4 5 6 Paxton, Leith; Bourne, David (1985). Locomotives of the South African Railways (1st ed.). Cape Town: Struik. pp. 84–85. ISBN 0869772112.
↑ Compounding Steam Engines
↑ The South African Railways - Historical Survey. Editor George Hart, Publisher Bill Hart, Sponsored by Dorbyl Ltd., Published c. 1978, p. 25.

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Locomotives of Natal

4' 8½" gauge	Natal 0-4-0ST Durban Natal 0-4-0WT Natal Natal 4-4-0T Perseverance

3' 6" gauge	Durban's Congella Durban's Edward Innes Durban's John Milne Durban's Sir Albert NGR Class A 1905 NGR Class A 1910 NGR Class B 4-8-0 1904 NGR Class B 4-8-0 1910 NGR Class B 4-8-2 1906 NGR Class B 4-8-2 1909 NGR Class B 4-8-2 1910 NGR Class C 4-8-2T NGR Class C 4-10-2T NGR Class D NGR Class E NGR Class F NGR Class G NGR Class H 4-6-2T NGR Class H 4-6-4T NGR Class I 2-6-0 NGR Class I 2-6-2T NGR Class K 0-4-0ST NGR Class K 0-6-0ST NGR Class K 2-6-0T NGR Class L 4-8-0 NGR Durban & Pietermaritzburg NGR Havelock NGR Mallet 1909 NGR Mallet 1910

2' gauge	NGR Class N 1906 NGR Class N 1907 NGR Class N 1911

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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