Italian State Railway class 690 II

Around 1910, the FS also realized that, thanks to superheater technology, compound engines could be dispensed with. Therefore the Pacifics of the class 690 II with four cylinders were commissioned. For the first time on a simple expansion locomotive in Italy, two adjacent cylinders used a common piston valve. The locomotives were designed for an axle load of 18 tonnes, but were ultimately manufactured with an axle load of only 17.1 tonnes for a better road availability.

The first nine were built with the driver's position on the right, the remaining 24 had it on the left. The firebox was partly located between the drivers and was therefore trapezoidal and narrow at the front. Since the grate had too small an area, the output was only 1,400 hp. Together with the axle load, which was still too high for most lines, no further class 690 locomotives were built. This led to a rebuild to class 691 at the end of the twenties and the class 695 to be developed as a successor.