South African Class 25 4-8-4

South African Class 25 4-8-4

No. 3511 at Hartswater, 24 April 1981

Type and origin Power type Steam Designer South African Railways (L.C. Grubb) Henschel and Son Builder Henschel and Son North British Locomotive Company Serial number Henschel 28730 NBL 27312-27400 Model Class 25 Build date 1953 Total produced 90 Rebuilder South African Railways Rebuild date 1973-1980 Number rebuilt 87 to Class 25NC

Specifications Configuration 4-8-4 (Northern) Driver 2nd coupled axle Gauge 3 ft 6 in (1,067 mm) Cape gauge Leading dia. 30 in (762 mm) Coupled dia. 60 in (1,524 mm) Trailing dia. 30 in (762 mm) Tender wheels 34 in (864 mm) Minimum curve 275 ft (84 m) Wheelbase 95 ft 1 11⁄16 in (28,999 mm)  • Engine 38 ft (11,582 mm)  • Leading 6 ft 10 in (2,083 mm)  • Coupled 15 ft 9 in (4,801 mm)  • Trailing 5 ft 6 in (1,676 mm)  • Tender 45 ft 10 in (13,970 mm)  • Tender bogie 10 ft (3,048 mm) Length: ​  • Over couplers 107 ft 6 1⁄16 in (32,768 mm) Height 13 ft (3,962 mm) Frame type Cast Axle load 19 LT 6 cwt (19,610 kg)  • Leading 21 LT 1 cwt (21,390 kg)  • 1st coupled 19 LT 4 cwt (19,510 kg)  • 2nd coupled 19 LT 5 cwt (19,560 kg)  • 3rd coupled 19 LT 6 cwt (19,610 kg)  • 4th coupled 19 LT 3 cwt (19,460 kg)  • Trailing 22 LT 10 cwt (22,860 kg)  • Tender bogie Bogie 1: 57 LT 4 cwt (58,120 kg) Bogie 2: 56 LT 14 cwt (57,610 kg)  • Tender axle 19 LT 1 cwt 2 qtr (19,380 kg) Adhesive weight 76 LT 18 cwt (78,130 kg) Loco weight 120 LT 9 cwt (122,400 kg) Tender weight 113 LT 18 cwt (115,700 kg) Total weight 234 LT 7 cwt (238,100 kg) Tender type CZ (3-axle bogies) Fuel type Coal Fuel capacity 19 LT (19.3 t) Water cap 4,400 imp gal (20,000 l) main tank 600 imp gal (2,730 l) condensate Firebox type Round-top  • Firegrate area 70 sq ft (6.5 m2) Boiler: ​  • Type Domeless  • Pitch 9 ft 1 5⁄8 in (2,784 mm)  • Diameter 6 ft 4 1⁄8 in (1,934 mm)  • Tube plates 19 ft (5,791 mm)  • Small tubes 158: 2 1⁄2 in (64 mm)  • Large tubes 40: 5 1⁄2 in (140 mm) Boiler pressure 225 psi (1,551 kPa) Safety valve Ross Pop Heating surface 3,390 sq ft (315 m2)  • Tubes 3,059 sq ft (284.2 m2)  • Arch tubes 37 sq ft (3.4 m2)  • Firebox 294 sq ft (27.3 m2) Superheater: ​  • Type Melesco  • Heating area 630 sq ft (59 m2) Cylinders Two Cylinder size 24 in (610 mm) bore 28 in (711 mm) stroke Valve gear Walschaerts Valve type Piston Valve travel 7 3⁄8 in (187 mm) Loco brake Vacuum Couplers AAR knuckle

Performance figures Tractive effort 45,360 lbf (201.8 kN) @ 75%

Career Operators South African Railways Class Class 25 Number in class 90 Numbers 3451-3540 Nicknames Condenser Delivered 1953-1954 First run 1953

The South African Railways Class 25 4-8-4 of 1953 was a condensing steam locomotive.

Between 1953 and 1955, the South African Railways placed ninety Class 25 condensing steam locomotives with a 4-8-4 Northern type wheel arrangement in service. The Class 25NC, which was placed in service at the same time, was a non-condensing version of the Class 25 condenser.

Owing to the difficulties experienced to obtain adequate supplies of suitable water in arid regions like the Great Karoo between Touws River and Kimberley and from De Aar into South West Africa (SWA), the South African Railways (SAR) began to give serious consideration to the possibility of introducing condensing locomotives as far back as the late 1930s. At one time, it was considered to convert Class 12A 4-8-2 locomotives to condensing engines, but this never happened.

Condensing locomotives were a rarity, but no novelty to South Africa, since the first condensing steam locomotives had already entered service in the Cape of Good Hope in the late nineteenth century. Between 1886 and 1888, three well-tank condensing locomotives with a 0-4-0 wheel arrangement were placed in service by the Cape Copper Mining Company on its Namaqualand Railway, a 2 ft 6 in (762 mm) gauge line between Port Nolloth and O'okiep.

On the SAR, it was only after the Second World War that extensive condensing tests were carried out with the modified Class 20 2-10-2 locomotive. The approximately 90% water and 10% coal savings which were achieved during the tests with the Class 20 in the Eastern Transvaal and the Karoo in 1950 and 1951, led to the decision to proceed with the design of a new condensing locomotive.