How Trains Stop

Feature

Railways

*Sachinder Mohan Sharma

Passenger profile on IR

Indian Railways carried about 8.4 Billion passengers in the year 2012-13 which is more than the total population of the world. These passengers clocked about 1.1 trillion passenger kilometers. About 53% of these passengers are suburban and the balance are long distance passengers.

How trains come to a stop?

We always wonder how trains run and how they are stopped. It is easy to understand how a car comes to a stop when the driver applies the brake using the brake pedal. Cars use hydraulic brakes whereas most of the trains in India use pneumatic brakes or air brakes as they are commonly called. These coaches are generally marked with an A or AB with the coach number. The trains can be stopped by the driver or by the passengers by alarm chain pulling (ACP).

In the Air Brake system, compressed air is used for operating the brake system. These brakes can be the conventional types or directly mounted on the bogies of the coaches. The latest design is the Disc Brake System (DBS) found in LHB coaches and is similar to what is found in automobiles. The atmospheric air is compressed in the locomotive upto 10 kg/cm2 and supplied at a pressure of 6/5 kg/cm2 to the train. It is carried across the whole length of the train through two pipes at the bottom of the coaches. When the brakes are applied the pressure in the 5kg pipe (the brake pipe) gets depleted proportionately and this causes the air to enter the brake cylinders which push a piston. The brake blocks are connected through a linkage and the piston movement causes them to stick to the wheels and stop the train by friction. The loss in pressure is made good by the air in the 6kg/cm2 pipe called the feed pipe. In case of disc brake system the pads attached to the discs are used to stop the train.

DBS is micro processor controlled and an advanced version of Air Brake system. It is essential for high speeds of 160kmph plus. It is superior in terms of reduced braking distance, higher wheel life due to reduced frequency of wheel turning, and reduced maintenance, less braking noise and higher efficiency due to simple brake rigging. The main characteristics of DBS are 02 discs mounted on each axle as shown in picture below:

Disc Brake Systm	Emergency Brake Handle

 When the passenger pulls the alarm chain shown above located near the seat it causes the pressure in the brake pipe to fall down giving an indication to the driver and stopping the train. A valve on the coach called the PEASD (passenger emergency alarm signal device) operates and the sound of the escaping air can be heard from the coach. Also a light near the door glows and indicates the location of the affected coach.

What does an unscheduled stoppage of a train by ACP mean to the public?

Have you ever wondered why trains are often delayed? Analysis shows that ACP contributes to 4% of the punctuality loss cases on Indian Railways. Imagine the social costs of the time delays to about 1500 passengers in a train when one pulls the chain for a valid or often illegitimate reason. Apart from this time loss, calculations show that for an extra stoppage of a 24 coach train travelling at 110 Kmph, the locomotive consumes an additional amount of approximately 130 litresof diesel fuel. This amounts to a loss of 8500 rupees as well as the increase in avoidable atmospheric pollution. As responsible citizens we should abstain from using ACP and should sensitize others not to do the same. The penalty for unauthorized use of the alarm chain is Rs.1000 and/or imprisonment up to three months.

Apart from this we need to realize that the train requires about one kilometer to stop due to its sheer momentum. It is for this reason that in spite of the driver being vigilant there are accidents on unmanned level crossings when trespassers break the rules and expect the train to stop immediately on seeing them.

As responsible citizens and enlightened green passengers we should refrain from using the ACP unless there is a dire emergency. It may be worthwhile to contact the railway staff on the train to solve the problem at hand.

*Sh. Sachinder Mohan Sharma, Director ME/E&R

Source:-PIB