South African Class GF 4-6-2+2-6-4

South African Class GF 4-6-2+2-6-4
No. 2427 at Mason's Mill, 6 July 1962
Type and origin ♠ Locomotives built by Hanomag ♥ Locomotives built by Henschel & Maffei Power type Steam Designer South African Railways (Col F.R. Collins DSO) Builder Hanomag Henschel and Son Maffei Serial number Hanomag 10512-10548 Henschel 21053-21070 Maffei 5748-5757 Model Class GF Build date 1927-1928 Total produced 65
Specifications Configuration: ​  • Whyte 4-6-2+2-6-4 (Double Pacific)  • UIC 2'C1'+1'C2'h4t Driver 2nd & 5th coupled axles Gauge 3 ft 6 in (1,067 mm) Cape gauge Leading dia. 30 in (762 mm) Coupled dia. 54 in (1,372 mm) Trailing dia. 30 in (762 mm) Wheelbase 69 ft 9 in (21,260 mm)  • Engine 23 ft 7 in (7,188 mm) each  • Leading 6 ft 2 in (1,880 mm) each  • Coupled 9 ft 6 in (2,896 mm) each Pivot centres 33 ft 2 in (10,109 mm) Length: ​  • Over couplers 77 ft 1 in (23,495 mm) Height 12 ft 10 in (3,912 mm) Frame type Bar Axle load ♠ 14 LT (14,220 kg) ♥ 14 LT 4 cwt (14,430 kg)  • Leading ♠ 18 LT 1 cwt (18,340 kg) front 19 LT 3 cwt (19,460 kg) rear ♥ 17 LT 7 cwt (17,630 kg) front 19 LT 3 cwt (19,460 kg) rear  • 1st coupled ♠ 13 LT 13 cwt (13,870 kg) ♥ 13 LT 19 cwt (14,170 kg)  • 2nd coupled ♠ 13 LT 9 cwt (13,670 kg) ♥ 13 LT 15 cwt (13,970 kg)  • 3rd coupled ♠ 13 LT 13 cwt (13,870 kg) ♥ 13 LT 19 cwt (14,170 kg)  • 4th coupled ♠ 13 LT 19 cwt (14,170 kg) ♥ 14 LT 4 cwt (14,430 kg)  • 5th coupled ♠ 13 LT 16 cwt (14,020 kg) ♥ 13 LT 19 cwt (14,170 kg)  • 6th coupled ♠ 14 LT (14,220 kg) ♥ 14 LT 4 cwt (14,430 kg)  • Trailing ♠ 11 LT 7 cwt (11,530 kg) front 12 LT 4 cwt (12,400 kg) rear ♥ 12 LT 3 cwt (12,340 kg) front 12 LT 8 cwt (12,600 kg) rear Adhesive weight ♠ 82 LT 10 cwt (83,820 kg) ♥ 84 LT (85,350 kg) Loco weight ♠ 143 LT 5 cwt (145,500 kg) ♥ 145 LT 11 cwt (147,900 kg) Fuel type Coal Fuel capacity 10 LT (10.2 t) (light rail) 11 LT 10 cwt (11.7 t) (Johannesburg-Mafeking) Water cap 3,000 imp gal (13,600 l) front 1,000 imp gal (4,550 l) rear Firebox type Round-top  • Firegrate area 44 sq ft (4.1 m2) Boiler: ​  • Pitch 7 ft 9 in (2,362 mm)  • Diameter 6 ft 2 3⁄4 in (1,899 mm)  • Tube plates 11 ft 8 5⁄8 in (3,572 mm)  • Small tubes 234: 2 in (51 mm)  • Large tubes 36: 5 1⁄2 in (140 mm) Boiler pressure 185 psi (1,276 kPa) Safety valve Pop Heating surface 2,242 sq ft (208.3 m2)  • Tubes 2,043 sq ft (189.8 m2)  • Arch tubes 23 sq ft (2.1 m2)  • Firebox 176 sq ft (16.4 m2) Superheater: ​  • Heating area 473 sq ft (43.9 m2) Cylinders Four Cylinder size 16 in (406 mm) bore 26 in (660 mm) stroke Valve gear Heusinger Valve type Piston Couplers AAR knuckle
Performance figures Tractive effort 34,200 lbf (152 kN) @ 75%
Career Operators South African Railways Class Class GF Number in class 65 Numbers 2370-2434 Delivered 1927-1928 First run 1927 Withdrawn 1979

The South African Railways Class GF 4-6-2+2-6-4 of 1927 was an articulated steam locomotive.

In 1927, the South African Railways placed 37 Class GF Garratt steam locomotives with a 4-6-2+2-6-4 Double Pacific type wheel arrangement in service. A further 28 locomotives were delivered from two manufacturers in 1928.

During the term of office of Colonel F.R. Collins DSO as Chief Mechanical Engineer of the South African Railways (SAR) from 1922 to 1929, articulated locomotives were in great favour in South Africa, to the extent that the Railway Board of the day instructed that non-articulated engines should only be ordered in exceptional circumstances.

The specifications for the Class GF 4-6-2+2-6-4 Garratt locomotive were prepared by Colonel Collins and an order for 37 locomotives was placed with Hannoversche Maschinenbau AG (Hanomag) in Germany. They were delivered in December 1927 and numbered in the range from 2370 to 2406.

A second order for eighteen locomotives was placed with Henschel and Son in 1927. They were delivered in October 1928, numbered in the range from 2407 to 2424.

This was followed by a third order, placed with Maffei in 1928, for a final batch of ten locomotives. They were delivered in November of that same year and numbered in the range from 2425 to 2434.

The locomotives were superheated, had bar frames, piston valves and used Walschaerts valve gear. The Class GF was the only Double Pacific type Garratt to see service on the SAR and, until the arrival of the Class GMA, was the most numerous Garratt locomotive class in SAR service. It was designed as a mixed traffic locomotive for use on branch lines and secondary mainlines throughout the country.

As built, the Class GF had inside bearings in their two-wheeled trailing trucks and considerable trouble was experienced with hot-boxes on these axles. Once these were modified to outside bearings, they proved to be very successful locomotives. Their good turn of speed and reasonably high tractive effort made the class a good utility locomotive.

From the establishment of the SAR in 1910, cabside engine number plates were inscribed "SOUTH AFRICAN RAILWAYS" in English only. This was still the case when the Class GF entered service, as seen on a Hanomag works picture of no. 2370. After the Official Languages of the Union Act No 8 of 1925 was passed on 8 May 1925, bilingual English and Afrikaans cabside number plates began to appear on locomotives, initially inscribed "SOUTH AFRICAN RAILWAYS" at the top and "SUID AFRIKANSE SPOORWEË" at the bottom, as shown. The Afrikaans spelling conventions were changed from time to time in the early years. On postage stamps, for example, it was "Zuid Afrika" from 1913, "Suidafrika" from the airmail stamps of 1925 and hyphenated "Suid-Afrika" from 1933. On cabside number plates, the Afrikaans inscription was later altered to "SUID AFRIKAANSE SPOORWEË" with the spelling of "AFRIKANSE" changed to "AFRIKAANSE", and still later to "SUID-AFRIKAANSE SPOORWEË" hyphenated.