South African Class MH 2-6-6-2

South African Class MH 2-6-6-2
SAR Class MH no. 1661, as depicted on a SAR Museum playing card
Type and origin
Power type	Steam
Designer	South African Railways
Builder	North British Locomotive Company
Serial number	20958-20962 ^[1]^[2]
Model	SAR Class MH
Build date	1915
Total produced	5
Specifications
Configuration	2-6-6-2 Mallet
Gauge	3 ft 6 in (1,067 mm) Cape gauge
Leading wheel diameter	28.5 in (724 mm)
Driver diameter	48 in (1,220 mm)
Trailing wheel diameter	33.5 in (851 mm)
Wheelbase	Total: 70 ft 10.25 in (21.596 m) Engine: 8 ft 8 in (2.642 m) per coupled set 43 ft 7 in (13.284 m) total Tender: 4 ft 7 in (1.397 m) bogie 16 ft 9 in (5.105 m) total
Length	79 ft 5 in (24.206 m)
Height	12 ft 10 in (3.912 m)
Axle load	18.2 long tons (18.5 t) per driver on rear engine unit
Weight on drivers	105.65 long tons (107.3 t)
Locomotive weight	128.25 long tons (130.3 t)
Tender weight	51.35 long tons (52.2 t)
Locomotive and tender combined weight	179.6 long tons (182.5 t)
Tender type	2 axle bogies 34 in (864 mm) wheels
Fuel type	Coal
Fuel capacity	10 long tons (10.2 t)
Water capacity	4,250 imp gal (19,300 l)
Boiler	5 ft 11 in (1.803 m) inside diameter 22 ft (6.706 m) inside length 7 ft 10.5 in (2.400 m) pitch
Boiler pressure	180 psi (1,240 kPa)
Firegrate area	53 sq ft (4.924 m²)
Heating surface: – Tubes	168 tubes 2.25 in (57.1 mm) diameter 25 tubes 5.5 in (140 mm) diameter 2,961 sq ft (275.086 m²)
– Firebox	250 sq ft (23.226 m²)
– Total	3,211 sq ft (298.312 m²)
Superheater area	634 sq ft (58.901 m²)
Cylinders	Four
High-pressure cylinder size	20 in (508 mm) bore 26 in (660 mm) stroke
Low-pressure cylinder size	31.5 in (800 mm) bore 26 in (660 mm) stroke
Valve gear	Walschaerts ^[3]
Performance figures
Tractive effort	48,370 lbf (215 kN) at 50% pressure
Career
Operator(s)	South African Railways ^[2]
Class	Class MH
Number in class	5
Number(s)	1661-1665 ^[2]
Delivered	1915
First run	1915
Withdrawn	1940

The South African Class MH 2-6-6-2 of 1915 is a South African steam locomotive from the South African Railways era.

In 1915 the South African Railways placed five Class MH Mallet articulated compound steam locomotives with a 2-6-6-2 wheel arrangement in service.^[2]^[3]

Manufacturer

The Class MH 2-6-6-2 Mallet articulated compound steam locomotive was designed in detail in the locomotive drawing office in Pretoria under the direction of D.A. Hendrie, Chief Mechanical Engineer (CME) of the South African Railways (SAR) from 1910 to 1922. Five of these very large locomotives were ordered from North British Locomotive Company (NBL) and delivered in 1915, numbered in the range from 1661 to 1665.^[2]^[3]

They were superheated and had Walschaerts valve gear. The locomotives were erected in the Salvokop shops in Pretoria and were placed in service in September 1915.^[2]^[3]

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, steam is expanded just once in any one cylinder before being exhausted through the smokebox.^[2]^[4]

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 that drive the front set of coupled wheels.^[2]^[3]

Characteristics

At the time of their introduction, the Class MH was the largest and most powerful locomotive in the world on Cape gauge. It attracted the attention of locomotive engineers throughout the world as an outstanding achievement for locomotive power on 3 feet 6 inches (1.067 metres) gauge.^[2]

Service

They were placed in service on the coal line between Witbank and Germiston that they were intended for, to supplement the other Mallets already working on that line. In the 1930s they were transferred to Natal to work on the line between Vryheid and Glencoe, also hauling coal. They were outstanding in their performance and remained in Natal for the rest of their service lives, until they were all retired and scrapped by 1940.^[2]^[3]

References

Wikimedia Commons has media related to:

South African Class MH (2-6-6-2)

↑ North British Locomotive Company works list, compiled by Austrian locomotive historian Bernhard Schmeiser
↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 Holland, D.F. (1972). Steam Locomotives of the South African Railways, Volume 2: 1910-1955 (1st ed.). Newton Abbott, Devon: David & Charles. pp. 30–32. ISBN 978-0-7153-5427-8.
↑ 3.0 3.1 3.2 3.3 3.4 3.5 Paxton, Leith; Bourne, David (1985). Locomotives of the South African Railways (1st ed.). Cape Town: Struik. p. 87. ISBN 0869772112.
↑ Compounding Steam Engines

Locomotives of South Africa

Steam

Brunel gauge	HBEL 0-4-0 HBTB 0-4-0T HBTB 0-4-0WT HBTB 0-4-0ST

Broad gauge	CGR Aid CGR Blackie CGR 0-4-2 CGR 2-4-0T NRC Durban NRC Natal NRC Perseverance

Cape gauge Tank	CGR Coffee Pot CGR 040 1873 CGR 040 1874 CGR 060 1876 CGR 060 1902 CGR 260 1900 CGR 260 1902 CGR 1st 040 1875 CGR 1st 440 1875 CGR 1st 040 1876 CGR 1st 260 1876 CGR 2nd 1882 CGR 3rd 1900 CGR RM CSAR C CSAR E CSAR Rack CSAR RM Dbn Congella Dbn Edward Innes Dbn John Milne Dbn Sir Albert HBPE 040 Kowie 060 Kowie 440 M&S 462 NGR Dbn & Pmb NGR I 262 NGR K 040 NGR K 060 NGR K 260 NZASM 10T NZASM 14T NZASM 18T NZASM 19T NZASM 32T NZASM 40T PPR 26T PPR 35T SAR RM SAR 0-4-0ST SAR 040 69 SAR A SAR B SAR C SAR C1 SAR C2 SAR D SAR E SAR F SAR G SAR H SAR H1 SAR H2 SAR J SAR K SWA 2-8-0T

Cape gauge Tender	CGR 1st 260 1876 BP CGR 1st 260 1876 K CGR 1st 260 1879 CGR 1st 440 1879 CGR 1st 1881 CGR 1st 1891 CGR 2nd 1875 CGR 3rd 1883 CGR 3rd 1884 CGR 3rd 1889 CGR 3rd 1898 CGR 3rd 1901 CGR 3rd 1903 CGR 4th 1880 CGR 4th 1882 CGR 4th 1884 CGR 4th 1897 CGR 5th 1890 CGR 5th 1891 NGR Havelock NGR I 260 Exp-1 Exp-2 Exp-3 Exp-4 Exp-5 Exp-6 SAR S SAR S1 SAR S2 SAR 1 SAR 1A SAR 1B SAR 2 SAR 2C SAR 3 SAR 3A SAR 3B SAR 4 SAR 4A SAR 5 SAR 5A SAR 5B SAR 6 SAR 6A SAR 6B SAR 6C SAR 6D SAR 6E SAR 6F SAR 6G SAR 6H SAR 6J SAR 6K SAR 6L SAR 6Y SAR 6Z SAR 7 SAR 7A SAR 7B SAR 7C SAR 7D SAR 7E SAR 7F SAR 8 SAR 8A SAR 8B SAR 8C SAR 8D SAR 8E SAR 8F SAR 8X SAR 8Y SAR 8Z SAR 9 SAR 10 SAR 10A SAR 10B SAR 10C SAR 10D SAR 11 SAR 12 SAR 12A SAR 12B SAR 13 SAR 14 SAR 14A SAR 14B SAR 14C SAR 15 SAR 15A SAR 15B SAR 15C SAR 15CA SAR 15E SAR 15F SAR 16 SAR 16A SAR 16B SAR 16C SAR 16D SAR 16DA SAR 16E SAR 17 SAR 18 SAR 19 SAR 19A SAR 19B SAR 19C SAR 19D SAR 20 SAR 21 SAR 23 SAR 24 SAR 25 SAR 25NC SAR 26 SWA 2-8-0

Cape gauge Articulated	CGR Fairlie CGR Kitson-Meyer SAR FC SAR FD SAR GA SAR GB SAR GC SAR GCA SAR GD SAR GDA SAR GE SAR GEA SAR GF SAR GG SAR GH SAR GK SAR GL SAR GM SAR GMA SAR GO SAR HF SAR KM SAR MA SAR MB SAR MC SAR MC1 SAR MD SAR ME SAR MF SAR MG SAR MH SAR MJ SAR MJ1 SAR U

2ft 6in gauge	CCC 1871 CCC Britannia CCC Caledonia CCC Clara CCC Condenser CCC Scotia NCC Pioneer

2ft & 600mm gauges	ACR NG-G16A CGR NG 060 CGR NG 462 CGR A CGR C NGR N SAR 040 1899 SAR NG1 SAR NG2 SAR NG3 SAR NG4 SAR NG5 SAR NG6 SAR NG7 SAR NG8 SAR NG9 SAR NG10 SAR NG-G11 SAR NG-G12 SAR NG-G13 SAR NG-G14 SAR NG15 SAR NG-G16 SWA Ha SWA Hb SWA Hc SWA Hd SWA Jung SWA Zwillinge

Diesel

-electric	SAR DS SAR DS1 SAR 31-000 SAR 32-000 SAR 32-200 SAR 33-000 SAR 33-200 SAR 33-400 SAR 34-000 SAR 34-200 SAR 34-400 SAR 34-500 SAR 34-600 SAR 34-800 SAR 34-900 SAR 35-000 SAR 35-200 SAR 35-400 SAR 35-600 SAR 36-000 SAR 36-200 SAR 37-000 SN 39-000 TFR 39-200 TFR 43-000 SAR 91-000 Afro4000

-hydraulic	SAR 61-000

Electro-diesel

SN 38-000

Electric