by Lochan Yadav
Any departure of track from the level is known as grade or gradient. An up or rising gradient is one when the track rises in the direction of movement whereas a falling or down gradient is one when the track falls in direction of the movement. Purpose of providing gradient:
To provide a uniform rate of rise or fall to the track.
To reduce the cost of earthwork.
To reach different stations at different elevations etc.
Types of gradient
The gradient used on railway 🚂 track can be classified into four categories as follows:
Pusher or helper gradient
The gradient at station yards
1) Ruling gradient: The steepest gradient allowed on the track section. It determines the max load that the locomotive can haul that section. The steep gradient needs more powerful locomotives, smaller train loads, lower speed, resulting in costly hauling. As a rule rising gradients should be followed by falling gradients. With this arrangement, the amount of energy used up in climbing is saved in descending.
In plains: 1 in 150 to 1 in 200
In hilly regions: 1 in 100 to 1 in 150
2) Momentum Gradient: The gradient on a section which is steeper than the ruling gradient acquires sufficient momentum to negotiate them are known as momentum gradient. For a momentum grade no obstacle like signal etc , Should be provided at critical points.
3) Pusher gradient: As stated above a ruling gradient limits the maximum weight of a train which can be hauled over the section by a locomotive. If the ruling gradient is so severe on a section that it needs the help of an extra engine to pull the same load then this gradient is known as the pusher of helper gradient. In Darjeeling Railways 1 in 37 pusher gradient is used on Western Ghat BG Track.
4) Gradient at stations: at stations gradient are provided sufficient low due to the following reason:
To prevent movement of standing vehicles on the track due to the effect of gravity combined with a strong wind or gentle push etc.
To prevent additional resistance due to grade on the starting vehicles which is about twice at the start than a vehicle in motion.
On Indian Railways, the maximum gradient permitted is 1 in 400 in station yards while in station yards a gradient of 1 in 100 is recommended.
🌠Grade compensation on curves:
If a curve is provided on a track with a ruling gradient, the resistance of the track will be increased. In order to avoid resistance beyond the allowable limits, the gradients are reduced on curves. The reduction in gradient is known as grade compensation for curves.
The recommended values for grade compensation are as follows.
BG track: 0.04% per degree of curve
MG track: 0.03 % per degree of curve
NG track: 0.02 % per degree of curve