South Australian Railways 720 class

The South Australian Railways 720 class was a class of 2-8-4 steam locomotives operated by the South Australian Railways.

South Australian Railways 720 Class
724 at North Adelaide station in 1952
Type and origin Power type Steam Designer Fred Shea Builder Islington Railway Workshops Build date 1930-1943 Total produced 17
Specifications Configuration: ​  • Whyte 2-8-4 1′D2′ 3′3′ Gauge 1,600 mm (5 ft 3 in) Leading dia. 2 ft 9 in (838 mm) Driver dia. 4 ft 9 in (1,448 mm) Trailing dia. 3 ft 0 in (914 mm) 3 ft 6 in (1,067 mm) Length 83 ft 6 in (25.45 m) Height 13 ft 11+5⁄8 in (4,256.1 mm) Axle load 19.85 long tons 0 cwt (44,500 lb or 20.2 t) Adhesive weight 77.10 long tons 0 cwt (172,700 lb or 78.3 t) Loco weight 123.80 long tons 0 cwt (277,300 lb or 125.8 t) Tender weight 104.00 long tons 0 cwt (233,000 lb or 105.7 t) Total weight 227 long tons 4 cwt (508,900 lb or 230.8 t) Fuel type Coal Oil Fuel capacity 17 long tons 0 cwt (38,100 lb or 17.3 t) 3,060 imp gal (3,670 US gal; 13,900 L) oil (locos converted to oil burning only) Water cap. 9,000 imp gal (11,000 US gal; 41,000 L) 9,400 imp gal (11,300 US gal; 43,000 L) (when oil fired) Firebox: ​  • Grate area 59.5 sq ft (5.53 m2) Boiler pressure 215 psi (1,482 kPa) Heating surface: ​  • Firebox 360 sq ft (33 m2)  • Tubes 2,615 sq ft (242.9 m2) Superheater: ​  • Heating area 751 sq ft (69.8 m2) Cylinders 2 Cylinder size 22 in × 28 in (559 mm × 711 mm) Valve gear Walschaerts valve gear Valve type Piston
Performance figures Tractive effort 43,450 lbf (193.28 kN) 52,000 lbf (231.31 kN) with booster engine cut in Factor of adh. 4.0
Career Operators South Australian Railways Class 720 Number in class 17 Numbers 720-736 First run 26/11/1930 Withdrawn 1958-1960 Scrapped 1958-1963 Disposition All scrapped

Design

The 720 class were built by the South Australian Railways as an improved version of the 710 class locomotives. The cylinders and running gear were broadly similar, but the boiler was enlarged and its pressure raised from 200 psi to 215 psi. The grate area was increased by nearly a third.

The 710 had been fitted with a Franklin C-2 booster engine on the trailing truck and this was repeated for the 720. However the additional weight of the booster had led to axle load problems on the lines laid with lighter 60 lb rail and some had their boosters removed. Partly to reduce this axle load, partly to support the increased weight of the enlarged firebox, the 720 changed from the 710's 2-8-2 Mikado wheel arrangement to a 2-8-4 Berkshire. The trailing wheels of this bogie were of different sizes, the larger rear wheels being driven by the booster and a smaller wheelset used under the front of the ashpan to give more clearance.

History

The initial order was for five locomotives. They were intended to operate on the lighter broad gauge lines, but after they began to spread rails, they were confined to the heavier lines. A further twelve were built between 1938 and 1943. The final twelve differed in having streamlined valances and boiler lagging tinwear. Coal shortages after World War II saw 14 converted to burn oil. All were later converted back to coal burners.

The last were withdrawn in April 1960.

Locomotive 720 at Islington Railway Workshops.