| South African Class MF 2-6-6-2 | |
|---|---|
| SAR Class MF 1627, ex CSAR 1023, circa 1912 | |
| Power type | Steam |
| Designer | American Locomotive Company |
| Builder | American Locomotive Company |
| Serial number | 49115-49123, 50039-50043[1] |
| Model | CSAR Superheater Mallet |
| Build date | 1910-1911 |
| Total produced | 14 |
| 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 | 46 in (1,170 mm) |
| Trailing wheel diameter |
28.5 in (724 mm) |
| Wheelbase | Total: 65 ft 6 in (19.964 m) Engine: 8 ft 4 in (2.540 m) per coupled set 40 ft 3 in (12.268 m) total Tender: 4 ft 7 in (1.397 m) bogie 17 ft 11 in (5.461 m) total |
| Length | 73 ft 7.25 in (22.435 m) |
| Height | 12 ft 10.375 in (3.921 m) |
| Frame | Bar frame |
| Axle load | 15.15 long tons (15.4 t) on 4th driver |
| Weight on drivers | 87.45 long tons (88.9 t) |
| Locomotive weight | 102.65 long tons (104.3 t) |
| Tender weight | 1619-1627: 55.2 long tons (56.1 t) 1629-1633: 51 long tons (51.8 t) |
| Locomotive & tender combined weight |
1619-1627: 157.85 long tons (160.4 t) 1629-1633: 153.65 long tons (156.1 t) |
| Tender type | 2 axle bogie Wheels 34 in (864 mm) dia |
| Fuel type | Coal |
| Fuel capacity | 10 long tons (10.2 t) |
| Water capacity | 1619-27: 5,000 imp gal (23,000 l) 1629-33: 4,000 imp gal (18,000 l) |
| Boiler | 6 ft 0.125 in (1.832 m) int dia 19 ft 10.125 in (6.048 m) int length 7 ft 9 in (2.362 m) pitch |
| Boiler pressure | 200 psi (1,380 kPa) |
| Firegrate area | 49.5 sq ft (4.599 m2) |
| Heating surface: Tubes |
151 tubes 2.25 in (57.2 mm) ext dia 25 tubes 5.375 in (137 mm) ext dia 2,459.6 sq ft (228.504 m2) |
| Heating surface: Firebox |
156 sq ft (14.493 m2) |
| Heating surface: Total |
2,615.6 sq ft (242.997 m2) |
| Superheater type | Schmidt |
| Superheater area | 559 sq ft (51.933 m2) |
| Cylinders | Four |
| High-pressure cylinder size |
18 in (457 mm) bore 26 in (660 mm) stroke |
| Low-pressure cylinder size |
28.5 in (724 mm) bore 26 in (660 mm) stroke |
| Valve gear | Walschaerts[2] |
| Tractive effort | 45,900 lbf (204.2 kN) at 50% boiler pressure[1] |
| Career | Central South African Railways South African Railways |
| Class | Class MF |
| Number in class | 14 |
| Number | CSAR 1015-1023 SAR 1619-1627, 1629-1633[1][3] |
| Delivered | 1911 |
| First run | 1911 |
| Withdrawn | 1939 |
| Disposition | Retired |
In 1911 the Central South African Railways placed nine Mallet articulated compound steam locomotives with a 2-6-6-2 wheel arrangement in service. In 1912, when they were assimilated into the South African Railways, they were renumbered and classified as Class MF. Five more of these locomotives were delivered in November 1911 and were numbered directly onto the South African Railways roster.[1][2][3]
Contents |
The nine Mallet articulated compound steam locomotives that were delivered to the Central South African Railways (CSAR) in 1911 were built by the American Locomotive Company (ALCO) between 1910 and 1911. They were very similar to the experimental Class MD that was delivered in 1910, but they were equipped with Schmidt superheaters. They had Walschaerts valve gear and were numbered 1015 to 1023.[1][2][3][4]
In 1912, when these locomotives were taken onto the South African Railways (SAR) roster, they were renumbered 1619 to 1627 and classified as Class MF. Five more of the type were delivered from ALCO in November 1911, but these were numbered 1629 to 1633 directly onto the SAR roster.[1][2][3]
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.[1][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 that drive the front set of coupled wheels.[1][2]
The Class MF joined the experimental Class MD on the coal traffic line between Witbank and Germiston. They were acquired to improve the traffic flow on this line with its ruling gradient of one in one hundred, where the increase of traffic and the resultant congestion was causing considerable delays en route that led to excessive hours of duty being imposed on crews. When they replaced the existing Class 11 locomotives on this line, train loads could be increased from 900 long tons (914 tonnes) to 1,600 long tons (1,626 tonnes).[1][2]
The Mallets proved to be capable of handling the heavy coal loads. In May 1914 Class MF number 1620 was used in a test run from Witbank to Germiston, hauling fifty-five bogie wagons with an all-up weight of 1,626 long tons (1,652 tonnes). The 80 miles (129 kilometres) journey was accomplished in seven hours, which included several stops.[1]
In 1923 engine number 1620 was converted to a simple expansion locomotive in the Koedoespoort shops in Pretoria. Five more, numbers 1621 to 1623, 1631 and 1632, were also converted to simplex locomotives in 1925. Three of these, numbers 1620, 1631 and 1632, were then transferred to East London where more powerful locomotives were needed since the line had a heavy gradient of one in forty that started right at the end of the departing platform, making it an extremely difficult section. They appear to have not been up to the task in the Eastern Cape, however, since by 1926 they were observed there, staged out of service.[1][2]
They were all withdrawn from service by 1939.[2]
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