Two Train Engines.

How do drivers of a train pulled by two engines control (the speed and braking) of the second engine when they are sitting in the first engine?

Two or more locomotives (engines) are used to haul a heavier train when power of a single locomotive is not adequate to pull the train either due to heavy loads, steeper gradients or higher speed required. Such operation is known as multiple unit or MU operation in short. Additional locomotives can be put either immediately behind the first loco or at the end of the train or sometimes even in the middle of the train. Such multiple set of locomotives are controlled by single set of crew (drivers) who are usually seated in the first locomotive for visibility or other reasons. Rest of the locomotives are controlled by a system known as locotrol (a mixed word for locomotive and control).

The locomotive in which the crew are seated is known as the master loco and the rest are slave locomotives. The master and the slave locomotives are electrically coupled through a set of cables and wireless signals (for such slave locomotives which are in the rear or in the middle of the train). The crew in the master loco sends electrical control signals to the slave locomotives through the cable or wirless system which actuates the electrical controls of all the slave locomotives together with the master locomotive. As far as braking is concerned, the system is much simpler. Brake operation in the modern trains is done by pressured air (at 5 kg per sq. cm.) which is fed to all the brake cylinders fixed under all wagons and the coaches (passenger vehicles) through a pressure pipe connected to the source of pressurised air in the locomotives. In the past, twin air pipes were used to increase the efficiency of brake application in longer trains. There are separate pipes for the locomotive brakes and the wagons/coaches. Application of brakes can be done from the leading locomotive or even the guard's van in the rear or from any of the slave locomotives. No electrical signals are needed for braking as the air flow in the pressure pipe is regulated by a mechanical handle.

C.S. Chakravarthy

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