The Locomotive Of Today

Ihe Fram ing, Wheels, etc.: Sanding Gear. 149 spring shoes; a disadvantage is, the links have to be made a very slack fit upon the pins, as the twisting movement upon them has to be allowed for, the lower ends of the links benig- fixed to the engine swing in a direction at right angles to its length, but the upper encls have to travel in a radial line struck from the centre of the pivot. The methods of obtaining flexibility by means of lateral movement, without any radial or revolving play, have been mentioned in the description of axle boxes. We will now consider some of the miscellaneous fittings necessary for the running equipment ot the locomotive. The hauling power depends upon the tractive force, that is, the power exerted by the steam acting upon the pistons in the cylinders transmitted through the mechanism of the engine to the drivers operating in conjunction with the adhesion, the latter representing the frictional resistance due to the weight placed upon the driving wheels. This must always be greater than the former, or the wheels will be made to revolve upon the rails, and “slip ” without moving the engine at all. With sufficient adhesion the wheels will revolve, and instead of slipping the whole engine and train to which it is attached will move along the rails in the direction desired. The adhesion or resistance to slipping- may, therefore, be said to be dependent upon the weight placed upon the drivers, but qualified by the condition of the rails. The friction between these two varies very considerably according as the latter are wet, dry or greasy. When dry and clean a tractive power exceeding one-fourth of the adhesive weight will cause slipping, when dry and sanded about one-third; in wet and frosty weather the friction is reduced to about one-sixth. Under ordinary working conditions—dry without sand, or wet with sanded rails, it is about one-fifth. In order to be able to work under the most advantageous conditions and obtain as mueh adhesion as possible, it is the practice to fit sand boxes upon the engine in convenient places for allowing sand to run upon the rails when there is a tendency for the drivers to slip. In Fig. 31 at A a sand box suitable for an engine with coupled wheels is shown. It is of cast iron, and is formed in one with the wheel splasher. The sand is filled in through the oval cover at the top, and is allowed to fali out by partially revolving a small “butterfly” valve at the bottom, which uncovers two holes over the sand pipe leading' to the front of the wheels. The gear necessary for working the valve is worked from a lever in the cab, and the sand is allowed to run on both rails at the same time, the rod shown in plan passing