Types of Gradient:
- Ruling gradient
- Momentum gradient
- Pusher gradient
- Station yard gradient
The ruling gradient is the maximum gradient to which the track may be laid in a particular section. It depends on the load of the train and additional power of the locomotive. The ruling gradients adopted:
- In plains – 1 in 150 to 1 in 200
- In Hilly tracks – 1 in 100 to 1 in 150
Gradient which is steeper than ruling gradient and where the advantage of momentum is utilized is known as momentum gradient. A train gets momentum when moving in downgradient and this momentum can be utilized for upgradient. A train while coming down a gradient gains sufficient momentum. This momentum gives additional kinetic energy to the moving train which would help the train to rise a steeper gradient than the ruling gradient for a certain length of the track. This rising gradient is called momentum gradient. In such gradients, no signals are provided to stop the train.
Pusher gradient is the gradient where an extra engine is required to push the train. These are steeper gradient than ruling gradient and are provided at certain places of mountains to avoid heavy cutting or to reduce the length of the track. A pusher gradient of 1 in 37 on Western Ghats with B.G. track is provided. On Darjeeling Railway with N.G. track, a ruling gradient of 1 in 25 is provided.
Station yard Gradient:
- Station yard gradient is the minimum gradient provided in station yard for easy draining of rainwater. Gradients are avoided as far as possible in station yard due to following reasons
- In station yard, Bogies standing on gradients may start moving due to heavy wind and may cause an accident.
- The locomotives will require an extra force of pull the train on gradients at the time of starting the trains.
- In station yards, the maximum limit of the gradient is fixed as 1 in 400 and minimum gradient recommended is 1 in 1000 for easy drainage of rainwater.
GRADE COMPENSATION OF CURVES:
Grade compensation on curves is the reduction in gradient on a curved portion of a track. On curves, the extra pull is required to pull the train due to more tractive resistance. Therefore, if gradients are to be provided on curves some compensation should be given in ruling gradients to overcome the increased tractive resistance to a certain limit and to pull the trains with the same speed. It is expressed as the percentage per degree of curve. The grade compensation provided on
- B.G. curves – 0.04percent /degree.