Engineering Wonders of the World
Volume I

ARTICULATED LOCOMOTIVES. 211 ARTICULATED LOCOMOTIVES. The term “ articulated ” is used in connec- tion with locomotives to describe all engines in which there are two or more sections—each steam-driven—connected together in such a way that one section can take up an angular position with respect to another section with- out difficulty when rounding sharp curves. Small locomotives can usually pass fairly severe curves quite safely; but there are numerous railways which contain sharp curves round which heavy traffic must be hauled by large, long, and powerful engines. In some cases the provision of side-play for the axles, or flangeless wheels, or radial axle-boxes, and bogies suffice. But under certain conditions the articulated locomotive alone meets the case. Fig. 40. FAIRLIE ARTICULATED LOCOMOTIVE, SAXON STATE RAILWAYS. Cylinders, 11] inches and 17| inches by 15J inches. Wheels, 30| inches diameter. Heating surface, 860 square feet. 40 tons. Ihese engines, built by the Saxon Machine Works, a,re designed for working light railway or tramway traffic • and as they pass in places along the public roads the mechanism is covered in. The boilers are connected by one large fire- box, a feature usual with Fairlie locomotives. 6 1 Fig- 41.—JOHNSTONE EIGHT-CYLINDER COMPOUND ARTICULATED LOCOMOTIVE FOR THE MEXICAN CENTRAL RAILWAY. This engine is somewhat of a freak, but affords a very remarkable example of a double-boiler articulated engine. The two sets of six-coupled wheels are mounted on pivoted frames, but the cylinders are carried on the main frames, and for trans- nutting power to the wheels require the use of special lever mechanism that will compensate for the swinging of the pivoted frames on curves. Four cylinders—two high and two low pressure—drive each set of coupled wheels. A peculiarity of the Johnstone compound system is to arrange a high-pressure inside a low-pressure cylinder. The latter has two piston rods which are attached to the same cross-head as the high-pressure rod. The engines of this type are so big that they had to be’ partly dismantled in order to get them through certain tunnels on the journey from the works to their sphere of action.