FS Class 685

FS Class 685
FS locomotive 685.089 in 2010
Type and origin Power type Steam Builder Ernesto Breda, Officine Meccaniche di Saronno, Reggiane Build date 1912–1928 Total produced 271 + 120 rebuilds
Specifications Configuration: ​  • UIC 1′C1′ h4 Gauge 1,435 mm (4 ft 8 1⁄2 in) standard gauge Leading dia. 960 mm (37.80 in) Driver dia. 1,850 mm (72.83 in) Trailing dia. 1,220 mm (48.03 in) Length 11,730 mm (38 ft 5 3⁄4 in) Axle load 15.1 tonnes (14.9 long tons; 16.6 short tons) Loco weight 70.8 tonnes (69.7 long tons; 78.0 short tons) Tender weight 49.6 tonnes (48.8 long tons; 54.7 short tons) Fuel type Coal Fuel capacity 6,000 kg (13,000 lb) Water cap 22,000 litres (4,800 imp gal; 5,800 US gal) Firebox:  • Firegrate area 3.5 m2 (38 sq ft) Boiler pressure 12 kg/cm2 (1,180 kPa; 171 psi) Heating surface 191.8 m2 (2,065 sq ft) Superheater: ​  • Heating area 48.54 m2 (522.5 sq ft) Cylinders Four, simple Cylinder size 420 mm × 650 mm (16.54 in × 25.59 in) Valve gear Walschaerts (early production), Caprotti (late production)
Performance figures Maximum speed 120 km/h (75 mph) Power output 1,250 CV (919 kW; 1,230 hp) Tractive effort 11,300 kgf (111 kN; 24,900 lbf)

FS Class S.685
FS locomotive S.685.600 as preserved
Type and origin Power type Steam Total produced 50 Rebuilder Ernesto Breda, Officine Meccaniche, FS Works of Pietrarsa Rebuild date 1929-1934
Specifications Configuration: ​  • UIC 1'C1'4h Gauge 1,435 mm (4 ft 8 1⁄2 in) Leading dia. 960 mm (3 ft 2 in) Driver dia. 1,850 mm (6 ft 1 in) Trailing dia. 1,220 mm (4 ft 0 in) Length 11,730 mm (38 ft 6 in) Axle load 17 tonnes (17 long tons; 19 short tons) Loco weight 73.4 tonnes (72.2 long tons; 80.9 short tons) Tender weight 54.1 tonnes (53.2 long tons; 59.6 short tons) Fuel type Coal Fuel capacity 5,500 kilograms (12,100 lb) Water cap 29,000 litres (7,700 US gal) Firebox:  • Firegrate area 3.5 square metres (38 sq ft) Boiler pressure 16 kilograms per square centimetre (230 psi) Heating surface 188.74 square metres (2,031.6 sq ft) Cylinders 4, simple Cylinder size 420 mm × 650 mm (16.54 in × 25.59 in) Valve gear Caprotti
Performance figures Maximum speed 120 kilometres per hour (75 mph) Power output 1,350 CV (990 kW; 1,330 hp) Tractive effort 11,800 kilograms-force (116 kN)

The Ferrovie dello Stato (FS; Italian State Railways) Class 685 (Italian: Gruppo 685) is a class of 2-6-2 'Prairie' express train steam locomotives. These are colloquially known as Regine ('Queens' in Italian), mirroring their fame as one of the most successful and appreciated Italian steam locomotives.

The Class 685 was the simple-expansion and superheated version of the pre-existing FS Class 680 locomotive, the premier express locomotive in Italy up to that date; while discarding the complicated compound feature, the 685 nonetheless kept the unusual feature of having the cylinders arranged in pairs, with each pair being served by a single piston valve with crossed ports (a feature typical of the Plancher engine of the Class 680 and other Italian locomotives).

The first 106 locomotives were built up to World War I, and had right-hand drive; construction resumed in 1920, and the remaining 165 were all built, up to 1928, with left-hand drive and a slightly longer boiler. Of the latter, 30 were built from the beginning with Caprotti valve gear, after it had been tested first on a FS Class 740 locomotive and then on other four 685 locomotives; all of these were initially reclassified as FS Class 686 locomotives, but were later placed again into the Class 685.

The Class 685 was present on all the Italian mainlines before their electrification, thanks to its good performance related to its moderate axle load. It was renowned as a well-balanced design, especially for its very smooth riding qualities, and was pretty much universally appreciated. Despite being express locomotives, especially in the waning years of the Italian steam they proved to be apt for freight train pulling as well.

The maximum authorized speed for the Class 685 locomotives was originally 110 km/h (68 mph); from 1932 it was raised to 120 km/h (75 mph).

The first units to be withdrawn from service, in the mid 1960s, were the heavier S.685 locomotives, and the more maintenance-requiring Caprotti and Franco-Crosti locomotives; the last unit in active service, the 685.222, was withdrawn in early 1975.

The by then-obsolete FS Class 680 locomotives were first subjected to a first rebuild, in which 91 of them were superheated but kept the compound engine (with some of them receiving a larger high pressure (HP) cylinder); after it was determined that these locomotives were still inferior in terms of performance and water and coal consumption, it was decided to rebuild them into Class 685 locomotives, instead.