Avoiding wheel lockup and sliding
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These are the general precautions to be taken to avoid wheel skidding or slipping.
Wheel skidding or sliding occurs when the wheels lock up with excessive braking pressure; this causes flat spots to develop on the circular wheel tread, which accentuates the skidding problem. This reduces the life of the wheels and causes the locomotive to be out of use for considerable amounts of time. Below are the precautions to be observed to avoid wheel skidding.
- In WAG-5 locomotives or other freight locomotive, the handle of the C3W distributor valve should be kept in the 'freight' position while working the goods train.
- Driving technique. According to the brake power of the train, efforts should be made to apply train brakes to control the train. A good driving technique is to apply the train brake only when possible, and at the same time to depress the PVEF to ensure that the locomotive brake does not come into action. In this way, the train is controlled on train brake power until a speed of 30km/h is reached. After the speed is reduced in this manner to 30km/h or so both the locomotive brake and the train brake are worked in conjunction by keeping the PVEF in the normal position. This process avoids wheel skidding. However, such a practice cannot be adopted in all cases as sometimes train control requires the use of loco brakes.
- The brake cylinder pressure should not be too high. The standard setting of the brake cylinder pressure is 3.5kg/cm^2. However, some sheds have reduced it to 3.0kg/cm^2 to reduce the pressure of the brake blocks on the wheels to reduce the chances of wheel skidding.
- The hardness of the brake block should be tested regularly and if it is found to be more than 180 to 200 BHN, the brake blocks should be replaced.
- The distributor valve should be adjusted for adequate time delay for brake application in locomotive, based on the train. This time delay should be 12 to 15 seconds for passenger service and 25 to 30 seconds for freight service.
- The locomotive should be tested for its brake power. If the locomotive does not move at a current of 850 to 900A, it indicates that the brake power is well beyond what is needed, and should be adjusted. (650A is the usual limit of current per traction motor where the brakes can hold the loco without moving.)