Hi, this is perhaps my favorite locomotive, as it is still exhibited on the shore of Lake Como today, since I was a child I asked my parents or aunts to take me to see it. The locomotives of group 851 were a group of steam locomotives of the State Railways (FS). They were designed and built by the Adriatic Network (RA) as machines for the line service. In 1905, together with the locomotives of the groups then FS 290, 600 and 870, also former RA, they were included among those that the FS considered worthy of further orders pending the completion of the projects of the new groups suitable to face the development of traffic travelers and goods resulting from nationalization. The advent of the 940 group locomotives relegated them to the role of shunting locomotives. With a geographical distribution complementary to that of the 835 group, these "interesting machines" served until the end of the era of steam traction in Italy in the seventies. For the services that were expected to be carried out on mountain lines with slopes up to 28 per thousand and numerous trunks armed with rails with a mass of 27 kg per meter. The steam generator was of the normal type in use at the time of design. The oven had a grill with an area of 1.53 m². The cylindrical body of the boiler was 4.41 m long (including the smoke chamber) and contained 213 3.2 m long boiler tubes between the furnace plate and the smoke chamber plate. The boiler, which contained 2.9 m³ of water, had a heating surface of 94.16 m², of which 87.8 m² of the boiler tubes and 6.36 m² of the part of the oven above the grill ( "sky of the oven"). It generated saturated steam with a production of 4 700 kg per hour. The engine was single expansion, with twin external cylinders, having 430 mm bore and 580 mm piston stroke, Walschaerts mechanism and spool valves. Like the FS 290 locomotives, all 851s were equipped with a variable escapement, however of the "pear" type The normal power was 294 kW at 30 km / h (this explains the subsequent use in maneuvers: in steam traction the power, and therefore the towable load, is maximum in the central range of developable speeds) The first sub-assembly was equipped with the vacuum brake. Subsequently, in compliance with legislative obligations, first the newly built machines and then the others were equipped with the Westinghouse type automatic and moderable compressed air brake, with installation of the compressor (single stage) on the right side. The last two photographs are the models produced by Rivarossi and Lima respectively
