The Brain of a Baldwin Diesel


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The brain of a Baldwin diesel is its throttle.

At first glance it may appear to be just a simple affair of an air pipe directly plugged into the governor fuel controller. In fact, the throttle performs many different functions all at the same time, and it is paired with a complex set of governor and electrical controls.

In addition to the standard running controls that work as a direct input/output on the diesel engine, a special Soft Starting feature is included on most Baldwin diesel locomotives. The soft starting feature is an extension of the main generator load control system that is operated by the exciter. A variable resistor, controlled by a special set of pneumatic relay valves, limits the generator output in the moments after the throttle is opened.

As soon as the throttle is switched "On" and power is applied, this resistor is set at it's maximum setting, and keeps the exciter and generator fields so week that they virtually don't exist. After a second or two, the air pressure acts on the resistor to lower it's resistance, thereby allowing the fields to strengthen and the generator output to increase. After a few more seconds, the air pressure holds the resistor at it's minimum setting so that full power can be applied.

When the throttle is closed, the air pressure vanishes, and the resistor resets to control another soft start. This resistor is also connected to the wheel-slip relay. When the wheels start to slip, the relay opens a valve that lets some of the air pressure to bleed off, which in turn acts to weaken the generator field and output with the same effect as reducing the throttle.

In a way, you can let the locomotive start itself with this system. Even if you cranked the throttle wide open as fast as you could, the engine would load up soft and easily, starting off with a gentle push before digging in and really starting to shove. Then when the power came up and the wheels started to slip, the load controller would automatically regulate power output to keep wheel-slip to a minimum.

Just tell her what you need and she'll do all the work for you!
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Thanks to Matthew Imbrogno for contributing this description.


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