A cog railway or rack-and-pinion railway is a mountain railway with a special centre rack rail mounted in the middle of the sleepers between the regular rails. The trains are fitted with one or more cog wheels that mesh into this rack rail (picture). This then allows the locomotives to haul the train up steeply inclined slopes.
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2 Cog locomotives 3 Cog railways 4 See Also |
A number of different rack systems have been developed:
Some rail systems, known as 'rack-and-adhesion', use the cog drive only on the steepest sections and elsewhere operate like a regular railway. Others are rack-only. On the latter type, the locomotives' wheels are generally free-wheeling and despite appearances do not contribute to driving the train whatsoever.
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 melt it, until it softens 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 is tilted forwards relative to the wheels, so that it is more or less horizontal when placed on the steeply graded track of the railway. These locomotives often cannot function on level track, and so the entire line must be laid on a gradient, including maintenance shops.
On a rack-only railroad locomotives always push their passenger cars, for safety since the locomotive is fitted with powerful brakes including, often, 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 pull the passenger car down against the locomotive.
Rack systems
The vast majority of cog railways use the Abt system.Cog locomotives
A cog steam locomotive showing the tilted boiler level on steeply graded trackCog railways
SchneebergbahnSee Also
