Steam Train - GR 740

he locomotives of the group 640 are steam locomotives with tender, of the State Railways, for passenger trains with 3 coupled drive axles and front load-bearing axle. The locomotives are the superheated steam and simple expansion version of the previous 630 group, with which they share most of the characteristics, including the internal two-cylinder engine, dimensions and three-axle tender. The boiler is of the same type as the 625 locomotive at 12 bars of pressure, produces the same quantity of steam and develops the same power of 800 HP; however, thanks to the drive wheels of greater diameter -1850 mm against 1,510 mm-, it reaches a speed of 100 km / h. The hourly production of dry steam is therefore equal to 6,500 kg. The oven, the grill and the heating and overheating surfaces are also the same as those of the 625. The motor cylinders have a diameter of 540 mm and a stroke of 700 mm. Steam distribution to the cylinders is of the piston type with Walschaerts system control lever. The machine develops a maximum tractive effort of 10,000 kg and at starting, under normal conditions of grip, equal to 6,290 kg; in motion at 75 km / h the tractive effort that can be developed continuously is 2,880 kg