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.In the period of the "second Conventions," between 1885 and 1905, passenger traffic on the network later merged into the FS increased from 1 782 000 to 4 575 000 pkm. In the same two decades, freight traffic increased from 1 695 000 to 4 997 000 tkm. In the decade to 1915 passenger traffic increased to 5 028 000 pkm and freight traffic to 8 874 000 tkm. Cf. Gennaro Trotta, Alcuni elementi statistici di attività ferroviaria italiana, in Ingegneria ferroviaria, 16 (1961), n. 7-8, p. 775.
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". served until the end of the steam traction era in Italy in the 1970s.
Background At the end of the nineteenth century, the completion of the Sulmona-Isernia and Candela-Potenza lines and the increase in train compositions and passenger car masses determined the management of the Adriatic Network to the design of a new group of steam locomotives intended to support, by placing at the head or rear of the trainsets, the tractive effortThis is a force measured at the periphery of the drive wheels or at the draw hook of vehicles. With other elements, it allows the determination of the towable load. of the titular machines especially on the steep pass lines. Therefore tank locomotives. with good adherent mass, power and speed and sufficient range for those types of services were studied.....For service on secondary lines with little traffic, the type of C arrangement tank locomotives at the time was the type preferred by engineers in charge of networks "all over Europe." Cf. Renzo Pocaterra, Treni, Novara, De Agostini Libri, 2011, p. 72.
Incorporated into the new RA 270 class and delivered in 1898 in an initial subgroup of 18 units, they were destined for the aforementioned Sulmona-Isernia and Candela-Potenza lines and the Terni-Ancona section of the Rome-Ancona and Pescara-Avezzano section of the Rome-Pescara.Ferrovie dello Stato. Direzione generale. Servizio Trazione, Album, cit., tav. 158.
Good operating results prompted the construction of a second subgroup in two separate lots of 18 and 24 units, which were delivered between 1900–01 and 1904...Ferrovie dello Stato. Direzione generale. Servizio Trazione, Album, cit., tav. 157.
The FS, which took over from the previous private companies in 1905, had to quickly set up plans for the development and renewal of their fleet."It must be acknowledged that the three large private networks, after 20 years of operation, at the termination of the Conventions returned to the state an organization in full fervor of renewal, but with scanty resources and, technically, no longer responsive to the needs of traffic that had instead taken on an unforeseen development." Cf. . While the Study and Testing Office of the Traction Service was designing new construction types while also taking up earlier studies, it was decided to commission more units of the pre-existing types possibly with modifications suggested by the practice of operation (FS classes 290, 320, 600, 630, 670, 750, 830, 851, 870, 904 and 910; in addition, they wanted to test U.S. construction techniques by ordering the 20 machines of classes 666 and 720)... Among them, former RA 270s were chosen, which formed the 851 FS class.In 1906, the FS had 287 C arrangement tank locomotives, of which some (FS Class 815) were built in 1853-1854. All, with the exception of 898, were designed for line services. Cf. .. Construction continued until 1911 for a total of 207 units, which from 1917 were numbered 851,001-207...
Project The design of RA 270 was developed by the Florence Study Office of the Adriatic Network and in some details shows a relationship to the contemporary 350 bis RA class, later FS 290.
As typical of the "Florentine school,"Having passed the first phase of the development of the Italian railway system, during which locomotives were purchased from the Italian and foreign manufacturing industries that had carried out the relevant designs, the two major railway companies began the independent design of their own vehicles. In particular, the Società Italiana per le Strade Ferrate Meridionali in 1880 established its own Office of Studies in Florence, which was inherited by the Adriatic Network and became the headquarters of the Material and Traction Service of the State Railways, aggregating to itself the staff and expertise of the corresponding Office established in Turin by the Società per le Strade Ferrate dell'Alta Italia in 1872, later acquired by the Mediterranean Network. Cf. .. simplicity of design was favored, especially of the engine and distribution mechanism. This choice generated significant economy of operation, which also had among its consequences a marked appreciation by the engine and shop personnel...
According to engineer Bruno Bonazzelli the RA 270, later named FS 851, can be considered the improved version of the RA 250, later named FS 827 class locomotives.Zeta-Zeta [Bruno Bonazzelli], L'album delle locomotive, in HO Rivarossi, 10 (1963), n. 57, p. 20. The opinion is shared by Giovanni Cornolò. and Gian Guido Turchi, who point out the common destination for reinforcement service, at the head or tail end of trains, on the steepest ramps of trans-Apennine lines.
Features For the services expected to be performed on mountain lines with gradients of up to 28 per thousand and numerous trunks armed with rails having a mass of ,. a running gear (UIC) C was chosen with wheels of diameter, spacing between extreme wheelsets of , all adhering mass, and a modest load per wheelset ( in the first subgroup and in the second subgroup)..
In the machines of the second subgroup, the consideration of the possibility of frequent stops for refueling prompted the reduction of water stocks from and coal stocks from (the increase in overall mass was due to the toughening of the chassis).
The steam generator was of the normal type in use at the time of design. The combustor had a grate with a surface area of . The cylindrical body of the boiler was long (including the smoke chamber) and contained 213 kettle tubes, long, between the furnace plate and the smoke chamber plate.Ferrovie dello Stato. Direzione generale. Servizio Trazione, Album, cit., tavv. 157-158.
The boiler, which contained of water, had a heating surfaceThrough which heat was transmitted to the water to be vaporized. of , including in the kettle tubes and in the part of the furnace above the grate ("furnace ceiling"). It generated saturated vapor with an output of per hour.
The engine was single-expansion,In a simple-expansion engine, the steam that drives the cylinders is introduced into them once and then expelled directly into the atmosphere or a condenser. The expansion phase lowers the temperature of the steam, resulting in cooling of the cylinder with each stroke and poor efficiency of the thermodynamic cycle (Rankine). with twin outer cylinders having a bore of and piston stroke of , Walschaerts mechanism, and slide valves.In slide valves, a drawer-shaped device, controlled by the connecting rod, opens and closes the steam introduction and exhaust channels in the engine cylinder.
Like the FS 290 locomotives, all 851s were equipped with a variable escapement of the "pear" type.The variable escapement allowed the engineer to change the forced draft by adjusting it to operating conditions and was typical of locomotives intended to run on lines with a rough profile. The "pear" or "cone" type received its name from the shape of the part, made of cast iron, that increased or decreased the diameter of the escapement column. Cf. , .
The normal power was at (this explains the later use in shunting: in steam traction the power, and thus the load that can be pulled, is maximum in the middle range of developable speeds).
The first subgroup was equipped with the vacuum brake. Later, in compliance with legislative requirements, first the newly built machines and then the others were equipped with the Westinghouse type automatic and proportional air brake,Introduced in Italy beginning in 1887. Cf. . with installation of the compressor (single stage) on the right side..The Adriatic Network had maintained and extended the use of the Smith-Hardy vacuum brake already used by the Strade Ferrate Alta Italia and Strade Ferrate Romane. From 1891 onward the General Inspectorate of Railroads, an organ of the Ministry of Public Works responsible for supervising the work of railway companies, first suggested and then decreed its replacement by the Westinghouse brake, whose use was generalized from 1905 by the FS. Cf. Maurizio Panconesi, Il freno Westinghouse. A 100 anni dalla scomparsa del suo inventore (1846-1914), in La tecnica professionale, n.s. 21 (2014), n. 1, pp. 38-46.
All machines were arranged to deliver steam for heating passenger cars.Steam heating was adopted by Italian railway companies from the late 19th century. It used a pipe fed by steam generated by the locomotive or a special vehicle (called a "heating wagon"), which circulated in radiators arranged in passenger compartments and corridors. It disappeared beginning in the 1930s, replaced by electric heating (with power supplied by the locomotive or a motor-generator vehicle). Cf. Gian Guido Turchi, Caldo sui treni, in I treni 15 (1994), n. 146, pp. 17-25, with a note by Erminio Mascherpa, I non facili primi passi del REC, ibidem, p. 23, P. Franchetto, M. Cerutti, I carri riscaldatori, in Tutto treno, 7 (1994), n. 66, pp. 12-17, with a note by Angelo Nascimbene, L'esperienza di un capodeposito istruttore del DL di Torino Smistamento dagli anni cinquanta fino agli ultimi servizi e ai carri "Vir", ibidem, pp. 16-17.
The machines of the first delivery had an open cab on the rear side, then enclosed with a wall equipped with three large windows, the middle one of which could be opened to increase ventilation in the cab.Zeta-Zeta [Bruno Bonazzelli], L'album delle locomotive, in HO Rivarossi, 10 (1963), n. 58, p. 26.
The paint schemes adopted were those normally used first by the RA and then by the FS.. The scheme, in gray, used provisionally for photographic shots for the purpose of documenting the activities of the manufacturing industries was applied to some..
Performance The performance assigned by the FS Material and Traction Service and published in the General Preface to the Service Schedule (PGOS) was the same for classes 851 and 981 (source:.):