South African Class ME 2-6-6-2

South African Class ME 2-6-6-2
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: ​  • Whyte 2-6-6-2 (Prairie Mallet)  • UIC (1'C)C1'h4 Driver 3rd & 6th coupled axles Gauge 3 ft 6 in (1,067 mm) Cape gauge Leading dia. 30 in (762 mm) Coupled dia. 42+1⁄4 in (1,073 mm) Trailing dia. 30 in (762 mm) Tender wheels 34 in (864 mm) Wheelbase 58 ft 5+1⁄2 in (17,818 mm) ​  • 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 66 ft 7+3⁄8 in (20,304 mm) Height 12 ft 10 in (3,912 mm) Frame type Plate Axle load 9 LT 18 cwt (10,060 kg) ​  • Leading 6 LT (6,096 kg)  • Coupled 9 LT 18 cwt (10,060 kg)  • Trailing 6 LT 14 cwt (6,808 kg)  • Tender bogie Bogie 1: 18 LT 4 cwt (18,490 kg) Bogie 2: 19 LT 8 cwt (19,710 kg)  • Tender axle 9 LT 14 cwt (9,856 kg) Adhesive weight 59 LT 8 cwt (60,350 kg) Loco weight 72 LT 2 cwt (73,260 kg) Tender weight 37 LT 12 cwt (38,200 kg) Total weight 109 LT 14 cwt (111,500 kg) Tender type XF (2-axle bogies) Fuel type Coal Fuel capacity 6 LT (6.1 t) Water cap. 3,000 imp gal (13,600 L) Firebox: ​  • Type Belpaire  • Grate area 32 sq ft (3.0 m2) Boiler: ​  • Pitch 7 ft 9 in (2,362 mm)  • Diameter 4 ft 1+3⁄4 in (1,264 mm)  • Tube plates 18 ft 6+1⁄2 in (5,652 mm)  • Small tubes 90: 2+1⁄4 in (57 mm)  • Large tubes 14: 5+1⁄4 in (133 mm) Boiler pressure 170 psi (1,172 kPa) Safety valve Ramsbottom Heating surface: ​  • Firebox 115 sq ft (10.7 m2)  • Tubes 1,340 sq ft (124 m2)  • Total surface 1,455 sq ft (135.2 m2) Superheater: ​  • Type 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 Johnston 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Career Operators South African Railways Class Class ME Number in class 1 Numbers 1618 Delivered 1912 First run 1912 Withdrawn 1937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.^[1][2][3][4]

During 1911, the Central South African Railways (CSAR) placed an order for a single experimental simple expansion Mallet articulated steam locomotive with the North British Locomotive Company (NBL). The locomotive was intended for test purposes on branch lines with light 45 pounds per yard (22 kilograms per metre) rail.^[1][2][3][5]

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.^[1][2][3][4]

Having been built for branch line working, the engine's maximum axle load was 9 long tons 18 hundredweight (10,060 kilograms) 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.^[2][6][7]

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.^[1][3][8]

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.^[2]

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.^[2]

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 engine.^[2]

The Class ME proved to be successful in operation and, even though it was acquired as an experimental locomotive, remained in service for 25 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.^[1]

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  Builder's works picture of no. 1618

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