Ferrovie dello Stato 4-6-2 Locomotives in Italy

Class Gruppo 690 (Locobase 2487)

"4-6-2 Four-Cylinder Locomotive, Italian State Railways," Locomotive Magazine, Volume XVII (15 July 1911), p. 150. See also Ugo Poddine as contributor to Bryan Attewell ([] Steam locomotive simulator (April 2000). .Additional data from diagram published on DUEGI EDITRICE's TuttoTreno website [], a modelling site with a great deal of data. (visited 11 July 2004). See also cnum_8XAE739, Exposition universelle, Groupe VII. Classes 39 et 40: Industrie des Transports-Chemins de fer et Tramways. Exposition internationale des industries et du travail de Turin 1911 (Paris: Comite Francais des Expositions a l'Etranger, 1911), p. 18.

Among the first Pacifics in Europe, these large and long-wheelbase engines served for years all over the Italian system. Later versions were fitted with Knorr feed water heaters.

The fire-side diameters of the fire tubes was 47 mm and of the flues was 125 mm. The resulting combined tube and flue heating surfaces was 2,260 sq ft (210 sq m).

They were later refined as the Grupo 691 class; see Locobase 3675.

Class Gruppo 691 (Locobase 3675)

Data from Ugo Poddine as contributor to Bryan Attewell ([] Steam locomotive simulator (April 2000). See also Nino Carbone, "Gr. 691 FS" entry posted 7 December 2013 in the Italia - Locomotive a vapore forum on the Marklinfan Club Italia website at [], last accessed 15 July 2021.

These 691 class Pacifics were upgrades of earlier 690s (Locobase 2487). The boiler is certainly bigger, although its length is the same and diameter is only 1" (25.4 mm) greater. Its steaming power increased considerably, wrote Nino Carbone, when the 300 deg C boiler originally installed was replaced one designed to steam at 400 deg C or higher when fitted with a superheater. Once trials had proved the new boiler's strength, the FS in 1930 raised the pressure setting from 14 bar to 16 bar.)

The new boiler was at first unsatisfactory because all of the tubes and flues had the same diameter of 64 mm (2.52"). The small tubes (those without superheater elements) later had diameters of 47 mm (1.85 mm).

The shops increased grate area by cutting off the ends of the frame and substituting a bolted assembly that took the weight of the new firebox on a reinforced joint.

A revamped Bissel truck with a longer pivot (2.25 m vs 1.525 m) came from the later editions of the Gr. 746 2-8-2 described in Locobase 2506. It required larger-diameter wheels.

The second and third series were built by Breda and the FS's own Florence shops in 1932-1934. A principal difference was the use of a two-stage Nielebock feed water heater pump.

Poddine describes it as the fastest and most powerful of Italian engines (passenger?), generating 1,750 hp at 55 mph (90 km/h). The 691.026 was built as a streamliner in 1937, but the shrouding was removed in 1941.