FS Class 685

Ferrovie dello Stato Italiane

Company type	State-owned company
Industry	Rail transport
Founded	1905
Headquarters	Rome , Italy
Area served	Italy

{{Infobox locomotive | name = FS Class 685 | bgcolor = 00625A | color = FFFFFF | image = Pistoia - deposito rotabili storici - locomotiva 685.089.jpg | caption = FS locomotive 685.089 in 2010 | powertype = Steam

| builder =

• Ernesto Breda (221)
• CEMSA (20),
• Officine Meccaniche, Milan (10)
• Officine Meccaniche e Navali (10)
• Reggiane (10)

| builddate = 1912–1928 | totalproduction = 271 + 120 rebuilds | uicclass = 1′C1′ h4 | gauge = Template:Track gauge | leadingdiameter = 960 mm (3 ft 1+3⁄4 in) | driverdiameter = 1,850 mm (6 ft 7⁄8 in) | trailingdiameter = 1,220 mm (4 ft 0 in) | length = 11,730 mm (38 ft 5+3⁄4 in) | axleload = 15.1 tonnes (14.9 long tons; 16.6 short tons) | locoweight = 70.8 tonnes (69.7 long tons; 78.0 short tons) | tenderweight = 48.6 tonnes (47.8 long tons; 53.6 short tons) | fueltype = Coal | fuelcap = 6,000 kg (13,000 lb) | watercap = 22 m³ (4,840 imp gal; 5,810 US gal) | boilerpressure = 12 kg/cm² (11.8 bar; 171 psi) | firearea = 3.5 m² (38 sq ft) | totalsurface = 191.8 m² (2,065 sq ft) | superheaterarea = 48.54 m² (522.5 sq ft) | cylindercount = Four, simple | cylindersize = 420 mm × 650 mm (16+9⁄16 in × 25+9⁄16 in)

| valvegear =

• Walschaerts (early production),
• Caprotti valve gear#Caprotti (late production)

| maxspeed = |maxspeed = |maxspeed = |maxspeed = |maxspeed = |maxspeed = |maxspeed = |maxspeed = |maxspeed = |maxspeed = |maxspeed = |maxspeed = |maxspeed = |maxspeed = |maxspeed = |maxspeed = |maxspeed = |maxspeed = 120 km/h (75 mph) |} The FS Class 685 (Template:Langx-it) is a series of 2-6-2 'Prairie' type steam locomotives designed for express trains, operated by the Ferrovie dello Stato Italiane (Italian State Railways). These engines earned the nickname Regine ('Queens' in Italian), reflecting their status as among Italy's most distinguished and well-regarded steam locomotives.

Design and construction

Derived from the earlier FS Class 680, which was Italy's foremost express steam locomotive at the time, the Class 685 represented a shift towards a simpler design featuring superheating but eliminating the complex Compound locomotive system. Despite this simplification, it retained the distinctive paired cylinder arrangement, where each pair was actuated by a single piston valve with crossed ports—a characteristic inherited from the Plancher system used on the Class 680 and other Italian models.Template:Sfnb Kalla-Bishop

Production of the initial batch of 106 units occurred before World War I, all equipped with right-hand drive configurations. Manufacturing recommenced in 1920, resulting in an additional 165 locomotives completed by 1928; these later models featured left-hand drive controls along with a marginally extended boiler. Among these later units, thirty were outfitted from the outset with Caprotti valve gear, following successful trials on a FS Class 740 engine and four earlier Class 685s fitted with this valve gear. Initially, these thirty were categorized as FS Class 686, but were subsequently reintegrated into the Class 685 roster.Template:Sfnb Kalla-Bishop

Operations

Prior to the electrification of Italy's principal railway lines, the Class 685 locomotives were a common sight, largely due to their favorable performance combined with a moderate axle load. They earned a reputation as well-rounded machines, particularly noted for their exceptionally smooth ride, which garnered widespread acclaim. Although primarily designed as express locomotives, during the later phase of Italian steam operations, they also demonstrated considerable capability in hauling freight trains.

Initially, the Class 685 engines were authorized to reach speeds up to 110 km/h (68 mph), but this limit was elevated to 120 km/h (75 mph) starting in 1932.

The earliest withdrawals occurred in the mid-1960s and involved the heavier S.685 models along with those equipped with Caprotti and Franco-Crosti valve gear systems, which demanded more intensive maintenance. The final unit in active service, number 685.222, was retired in early 1975.

Rebuilds from the 680 class

The FS Class 680 locomotives, considered outdated by that time, initially underwent a first phase of modernization where 91 units were fitted with superheaters but retained their compound engine design—some even received an enlarged high-pressure cylinder. However, these modifications did not yield satisfactory improvements in performance or fuel and water efficiency. Consequently, a decision was made to convert them into Class 685 locomotives.

The initial batch of 31 rebuilt locomotives, renumbered as 685.3XX, featured both superheaters and simple-expansion engines while maintaining the original boiler pressure of 16 kg/cm² (15.7 bar; 228 psi). These units exhibited greater power than the original Class 685s due to their elevated boiler pressure. Subsequently, an additional group of 40 locomotives classified as 685.5XX were upgraded with Caprotti valve gear and boilers capable of producing even higher steam temperatures to enhance efficiency; some were also equipped with exhaust injectors.

Class S.685

The final series of rebuilds aimed at deployment on mainlines where previous axle load restrictions had been lifted underwent modifications to increase adhesive weight by repositioning the pivots of both the Italian bogie and trailing axle closer to the driving wheels. This adjustment raised the axle load to 17 tons and improved overall performance. Taking advantage of relaxed weight constraints, these locomotives were also outfitted with Knorr pre-heaters; some received larger tenders with a water capacity of 29,000 L (7,700 US gal), similar to those used on the FS Class 691. A total of 49 units were rebuilt by 1933, and in 1934 one locomotive numbered 685.500 was further converted into an S.685 model. Due to their enhanced capabilities—comparable or occasionally superior to the larger FS Class 690 Pacifics—these machines were designated as Class S.685 (with 'S' denoting Speciale).

Class S.685 locomotives primarily served on major routes such as Milan-Venice, Milan-Turin, and Rome-Naples (via Cassino), notably sharing duties on the Milan-Venice line with the FS Class 691. Following electrification of these lines in 1958 and 1961 respectively, their higher axle load combined with increased maintenance requirements led to their retirement by 1968.

Ultimately, a total of 120 former Class 680 locomotives were rebuilt by 1933, bringing the overall number within Class 685 to 391 units.

Franco-Crosti

In 1939, five locomotives equipped with Caprotti valve gear underwent modifications to incorporate Franco-Crosti boilers. These units were initially designated as Class S.685, but in 1951, they were reclassified under the FS Class 683 category.Template:Sfnb

Turbine locomotive

The locomotive numbered 685.410 was fitted in 1933 with a large steam turbine for forward movement and a smaller turbine for reverse, replacing its original cylinders. This trial, overseen by the distinguished engineer Giuseppe Belluzzo, proved unsuccessful, leading to the restoration of the original cylinder configuration in 1934.Template:Sfnb

Preservation

A total of five Class 685 locomotives have been preserved:

• Locomotives 685.089 and 685.196 remain operational;
• The 685.068 is displayed as a static exhibit at the Pietrarsa railway museum;
• The S.685.600, notable as the 1000th locomotive produced by the Ernesto Breda company, is exhibited statically at the Museo della Scienza e della Tecnologia "Leonardo da Vinci";
• Locomotive 685.222 serves as a parts donor at Pistoia.

Bibliography

• Template:Kalla-Bishop-FS-Steam