Rack Railway - Cog Locomotives

Cog Locomotives

Originally almost all cog railways were powered by steam locomotives. The steam locomotive needs to be extensively modified to work effectively in this environment. Unlike a diesel locomotive or electric locomotive, the steam locomotive only works when its powerplant (the boiler, in this case) is fairly level. The locomotive boiler requires water to cover the boiler tubes and firebox sheets at all times, particularly the crown sheet, the metal top of the firebox. If this is not covered with water, the heat of the fire will soften it enough to give way under the boiler pressure, leading to a catastrophic failure.

On rack systems with extreme gradients, the boiler, cab and general superstructure of the locomotive are tilted forward relative to the wheels so that they are more or less horizontal when on the steeply graded track. These locomotives often cannot function on level track, and so the entire line, including maintenance shops, must be laid on a gradient. This is one of the reasons why rack railways were among the first to be electrified and most of today's rack railways are electrically powered. In some cases, the vertical boiler can be used that is less sensitive for the track gradient.

On a rack-only railroad locomotives always push their passenger cars for safety reasons since the locomotive is fitted with powerful brakes, often including hooks or clamps that grip the rack rail solidly. Some locomotives are fitted with automatic brakes that apply if the speed gets too high, preventing runaways. Often there is no coupler between locomotive and train since gravity will always push the passenger car down against the locomotive. Electrically powered vehicles often have electromagnetic track brakes as well.

The maximum speed of trains operating on a cog railway is very low, generally from 9 to 25 km/h depending on gradient and propulsion method. Because the Skitube has gentler gradients than typical, its speeds are higher than typical.