South African Class ME 2-6-6-2

South African Class ME 2-6-6-2

300px Class ME no. 1618, c. 1912

Type and origin Power type Steam Designer North British Locomotive Company Builder North British Locomotive Company Serial number 19355 Model CSAR Mallet Build date 1912 Total produced 1

Specifications Configuration 2-6-6-2 (Prairie Mallet) Driver axle 3rd & 6th coupled axles Gauge 3 ft 6 in (1,067 mm) Cape gauge Leading dia 30 in (762 mm) Coupled dia Trailing dia 30 in (762 mm) Tender wheels 34 in (864 mm) Wheelbase  • Engine 38 ft 3 in (11,659 mm)  • Coupled 8 ft 6 in (2,591 mm) per unit  • Tender 14 ft 7 in (4,445 mm)  • Tender bogie 4 ft 7 in (1,397 mm) Length:  • Over couplers Height 12 ft 10 in (3,912 mm) Frame type Plate Axle load  • Leading  • Trailing  • Tender bogie Bogie 1: Bogie 2:  • Tender axle Adhesive weight Loco weight Tender weight Loco & tender weight Tender type XF (2-axle bogies) Fuel type Coal Fuel capacity 6 LT (6.1 t) Water cap Boiler:  • Pitch 7 ft 9 in (2,362 mm)  • Diameter  • Tube plates  • Small tubes 90:  • large tubes 14:  • Firebox type Belpaire Boiler pressure 170 psi (1,172 kPa) Safety valve Ramsbottom Firegrate area 32 sq ft (3.0 m2) Heating surface 1,455 sq ft (135.2 m2)  • Tubes 1,340 sq ft (124 m2)  • Firebox 115 sq ft (10.7 m2) Superheater Schmidt  • Heating area 346 sq ft (32.1 m2) Cylinders Four Cylinder size 15 in (381 mm) bore 23 in (584 mm) stroke Valve gear Walschaerts Valve type Piston Couplers Bell link-and-pin

Performance figures Tractive effort 31,230 lbf (138.9 kN) @ 50%

Career Operators South African Railways Class Class ME Number in class 1 Numbers 1618 Delivered 1912 First run 1912 Withdrawn 1937

The South African Railways Class ME 2-6-6-2 of 1912 was a steam locomotive.

In January 1912, the South African Railways placed a single Class ME Mallet articulated steam locomotive with a 2-6-6-2 wheel arrangement in service.

Manufacturer

During 1911, the Central South African Railways (CSAR) placed an order for an experimental simple expansion Mallet articulated steam locomotive with the North British Locomotive Company (NBL). The locomotive was intended for test purposes on branchlines with light 45 pounds per yard (22 kilograms per metre) rail.

By the time it was delivered in January 1912, the CSAR had already become part of the newly established South African Railways (SAR). The locomotive was therefore classified as the sole Class ME and numbered 1618 on the SAR roster.

Characteristics

Having been built for branchline working, the engine's maximum axle load was and it was delivered with the 6 long tons (6.1 tonnes) coal capacity version of the Type XF tender. Its Belpaire firebox extended over the second and third coupled wheels of the rear engine unit.

Compared to other Mallet locomotives which were placed in service during the first decade of the SAR’s existence, the Class ME was unique in being arranged as a simple expansion (simplex) locomotive with four high pressure cylinders, instead of the more usual compound expansion arrangement of two high pressure and two low pressure cylinders.

The cylinders were arranged outside the plate frames and the 6 inches (152 millimetres) diameter trick-ported piston valves, designed for inside admission, were actuated by Walschaerts valve gear. Each engine unit was equipped with an independent Wakefield mechanical lubricator to supply oil to the valves and pistons.

The comparatively low boiler pressure of 170 pounds per square inch (1,172 kilopascals) is indicative of the opinion held at the time, that the economies to be gained from superheating did not require high boiler pressure. The boiler was equipped with a Schmidt superheater. Steam distribution to the four cylinders was rather unique, being led from the superheater header in the smokebox to a steam collector box, which was arranged between the two cylinders of the rear engine unit, from where a branch was led to the cylinders of the front engine unit by a central steam pipe with flexible joints, since this engine unit could move sideways in relation to the boiler barrel. This pipe took the place of the usual receiver pipe on compound Mallets.

The blast pipe had separate outlets for the exhaust steam from each engine unit, with the rear engine unit's exhaust feeding through an annulus, arranged around the exhaust from the front engine unit. A device was installed by which either engine unit could be cut out whilst running, so that steam could be admitted to one pair of cylinders only, when running light.

Service

The Class ME proved to be successful in operation and, even though it was acquired as an experimental locomotive, remained in service for twenty-five years. It spent its last years working on the line from Nelspruit to Sabie in the Eastern Transvaal Lowveld, until it was withdrawn and scrapped in 1937.

Illustration

• Class ME no. 1618.jpg

  Builder's works picture of no. 1618