The Locomotive Of Today

178 The Tender, Brakes, etc. : Rack-rail Locomotives. On steeper grades still, where adhesion alone would not be sufficient however applied, “rack” engines are used. The track for this type of locomotive is laid with ordinary rails for carrying the engines and cars, while another or third “ rack rail ” is placed between, having large teeth, or steps, in which a “ cog ” on the engine engages. The locomotive is provided with an engine similar in design to that ordinarily used but constructed to drive a shaft, which carries the “cog” wheels; these gear into the rack and enable the load to be hauled, and will hold the engine immovable in any position it may be stopped in, assisting in the safety of working up or down the steepest grades. Engines of this type used on mountain railways are not turned rouncl at the end of a trip, but con- tinually run with the chimney towards the top of the gradient, and as the inclination of the rails is great the water level in the boiler would be very low at the firebox end if the boiler was placed parallel with the rails. It is therefore set at an angle with them, the amount of inclination, of course, depend- ing upon the gradients to be surmounted. On engines operating entirely on rack rails, the smooth rails benig required for carrying and guidance only, the wheels bearing upon these may be loose upon the axles, thus allowing great freedom for the engine upon curves ; but when the ordinary rails and sharp grades alternate, a double set of engines are provided—one for working the rack wheels, and another for the adhesion wheels, which in this case are coupled together by side rods. These two engines are entirely inde- penclent of each other, and the driver can use either of them at will as the severity of the road demands.