How Diesel Locomotives Work

Driving a Locomotive

You don't just hop in the cab, turn the key and drive away in a diesel locomotive. Starting a train is a little more complicated than starting your car.

The engineer climbs an 8-foot (2.4-m) ladder and enters a corridor behind the cab. He or she engages a knife switch (like the ones in old Frankenstein movies) that connects the batteries to the starter circuit. Then the engineer flips about a hundred switches on a circuit-breaker panel, providing power to everything from the lights to the fuel pump.

Next, the engineer walks down a corridor into the engine room. He turns and holds a switch there, which primes the fuel system, making sure that all of the air is out of the system. He then turns the switch the other way and the starter motor engages. The engine cranks over and starts running.

Next, he goes up to the cab to monitor the gauges and set the brakes once the compressor has pressurized the brake system. He can then head to the back of the train to release the hand brake.

Finally he can head back up to the cab and take over control from there. Once he has permission from the conductor of the train to move, he engages the bell, which rings continuously, and sounds the air horns twice (indicating forward motion).

The throttle control has eight positions, plus an idle position. Each of the throttle positions is called a "notch." Notch 1 is the slowest speed, and notch 8 is the highest speed. To get the train moving, the engineer releases the brakes and puts the throttle into notch 1.

In this General Motors EMD 710 series engine, putting the throttle into notch 1 engages a set of contactors (giant electrical relays). These contactors hook the main generator to the traction motors. Each notch engages a different combination of contactors, producing a different voltage. Some combinations of contactors put certain parts of the generator winding into a series configuration that results in a higher voltage. Others put certain parts in parallel, resulting in a lower voltage. The traction motors produce more power at higher voltages.

As the contactors engage, the computerized engine controls adjust the fuel injectors to start producing more engine power.

The brake control varies the air pressure in the brake cylinders to apply pressure to the brake shoes. At the same time, it blends in the dynamic braking, using the motors to slow the train down as well.

The brake and throttle controls

The engineer also has a host of other controls and indicator lights.

Controls, indicators and the radio

A computerized readout displays data from sensors all over the locomotive. It can provide the engineer or mechanics with information that can help diagnose problems. For instance, if the pressure in the fuel lines is getting too high, this may mean that a fuel filter is clogged.

This computerized display can show the status of systems all over the locomotive.

Now let's take a look inside the train.