FS Class 851

FS 851
FS locomotive 851.186 on display in Como's public gardens, May 2013
Type and origin Power type Steam Builder Gio. Ansaldo & C. (25) Società Italiana Ernesto Breda (32) Maffei (16) CM de Saronno (79) Officine Meccaniche (58) Build date 1898-1911 Total produced 207
Specifications Configuration: ​  • Whyte 0-6-0T  • UIC C n2t Wheel diameter 1,510 mm (4 ft 11+1⁄2 in) Wheelbase: ​  • Axle spacing (Asymmetrical) 2,000 mm (6 ft 6+3⁄4 in) 2,000 mm (6 ft 6+3⁄4 in)  • Engine 4,000 mm (13 ft 1+1⁄2 in) Length: ​  • Over headstocks 7,850 mm (25 ft 9 in)  • Over buffers 9,000 mm (29 ft 6+3⁄8 in) Height 4,225 mm (13 ft 10+3⁄8 in) Axle load 14.7 tonnes (14.5 long tons; 16.2 short tons) Loco weight 43 or 44 tonnes (42 or 43 long tons; 47 or 49 short tons) Boiler: ​  • Pitch 2,140 mm (7 ft 1⁄4 in) Boiler pressure 12 kgf/cm2 (11.8 bar; 171 psi) Heating surface: ​  • Firebox 1.53 m2 (16.5 sq ft) Superheater: ​  • Heating area 83.3 or 94.16 m2 (896.6 or 1,013.5 sq ft) Cylinders Two, outside Cylinder size 430 mm × 580 mm (16+15⁄16 in × 22+13⁄16 in)
Performance figures Maximum speed 65 km/h (40 mph) Power output: ​  • Continuous 400 PS (294 kW; 395 hp) Tractive effort 6,950 kgf (15,300 lbf)

Class 851 locomotives were a class of steam locomotives of the Italian State Railways (FS).

They were designed and built by the Adriatic Network (RA) as machines for line service. In 1905, together with the locomotives of the classes FS 290, 600 and 870 ex-RA, they were included among those that the FS deemed worthy of further orders pending the completion of the designs of new classes suitable to cope with the development of passenger and freight traffic resulting from nationalization.^{[note 1]}

The advent of Class 940 locomotives relegated them to the role of shunting locomotives. With a geographical distribution complementary to that of class 835, these "interesting machines"^[1] served until the end of the steam traction era in Italy in the 1970s.

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