FS Class 746
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FS locomotive 746.031 as preserved
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| Type and origin | |
|---|---|
| Power type | Steam |
| Builder |
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| Build date | 1923–1927 |
| Total produced | 60 |
| Specifications | |
|---|---|
| Configuration: |
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| • UIC | 1′D1′ h4v |
| Gauge | 1,435 mm (4 ft 8 1⁄2 in) standard gauge |
| Leading dia. | 1,110 mm (43.70 in) |
| Driver dia. | 1,880 mm (74.02 in) |
| Trailing dia. | 1,125 mm (44.29 in) |
| Length | 14,085 mm (46 ft 2 1⁄2 in) |
| Axle load | 16.2 tonnes (15.9 long tons; 17.9 short tons) |
| Loco weight | 98.8 tonnes (97.2 long tons; 108.9 short tons) |
| Tender weight | 49.6 tonnes (48.8 long tons; 54.7 short tons) |
| Fuel type | Coal |
| Fuel capacity | 6,000 kg (13,000 lb) |
| Water cap | 22,000 litres (4,800 imp gal; 5,800 US gal) |
| Firebox: • Firegrate area |
4.3 m2 (46 sq ft) |
| Boiler pressure | 16 kg/cm2 (1.57 MPa; 228 psi) |
| Heating surface | 237 m2 (2,550 sq ft) |
| Superheater: |
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| • Heating area | 112 m2 (1,210 sq ft) |
| Cylinders | Four, compound |
| High-pressure cylinder | 490 mm × 680 mm (19.29 in × 26.77 in) |
| Low-pressure cylinder | 720 mm × 680 mm (28.35 in × 26.77 in) |
| Valve gear | Walschaerts, Caprotti |
| Performance figures | |
|---|---|
| Maximum speed | 100 km/h (62 mph) |
| Power output | 1,750 CV (1,290 kW; 1,730 hp) at 75 km/h (47 mph) |
| Tractive effort | 14,000 kgf (137 kN; 30,900 lbf) |
The Ferrovie dello Stato Italiane (FS; Italian State Railways) Class 746 (Italian: Gruppo 746) is a class of 2-8-2 'Mikado' steam locomotive.
The Class 746 originated from the need of a fast locomotive that, while having similar performance to the 'Pacific' Class 690, could have a lower axle load and therefore wider route availability; this could be achieved by adding another driving axle, and accepting a lower top speed (reverting to a leading Italian bogie). To achieve high performance, it was decided to adopt a symmetric compound engine (a Von Borries design), with the two inside high pressure (HP) cylinders having the motion for their valves derived from the outside Walschaerts valve gear; this was unusual for Italian locomotive practice, where the compound engine had been shelved once the superheating technology had become available in the 1910s.
Forty locomotives were ordered to the Ernesto Breda, which produced them in 1922, and then ten more in 1926; Gio. Ansaldo & C. built ten more, fitted with Caprotti valve gear, in the same years. The latter were initially classified as Class 747, but in 1930 they were reclassified as the 746.100-110 subclass.
The Class 746 initially operated on the Milan-Bologna-Florence-Rome-Naples main line; after portion of it were electrified, they served on the Milan-Turin and the Milan-Brescia railways. In the 1960s they were operating in Sicily and on the Adriatic coast railway, until their withdrawals, which were concluded by 1967. While fast, powerful and suitable for both fast passenger and goods trains, the Class 746 proved difficult to start and somewhat uneasy when running at or close to its top speed (with both problems originating from its compound engine); also, at higher speeds the low-pressure cylinders contributed relatively little to the locomotive's power output. The locomotives fitted with Caprotti valve gear also turned out to have problems when functioning in reverse.
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Wikipedia