KB311: Diesel Notches

This article was last updated on Jan. 18, 2012, 10:27 a.m. | Print Article | Leave Feedback


Could you please explain what the notch rate does- is there a range for this?

Is there somewhere with more detailed explanations of the various CV's- such what what the air drier or compressor rate might be?

Diesel locomotives are operated by "notches", which are the rate at which the locomotive's diesel power is being applied.

Traditionally, these are called "Run 1" to "Run 8".

At Run 1, the locomotive generator becomes active but the locomotive prime mover (the diesel engine) does not increase in speed.

With Run 2 to Run 8, the locomotive's engine speed (and thus the sound) increases.

It should be noted that a fast moving train may not necessarily be in Run 8, since the momentum of the train may be pushing it along at high speed without power application.

Likewise, a locomotive running downhill may be in Run 8, but using its dynamic brakes to slow the train without using the shoe brakes.

As could be expected, there are some interesting exceptions, such as with earlier GE locomotives, which have 16 notches, but because they were often operated with other manufacturers' locomotives, they too usually operated in the 8 notch format.

And modern locomotives use a different approach to power; in some cases, the locomotive may be in Run 8, but not be moving since it is providing head-end power (HEP) to the passenger cars it is pulling.

There's nothing quite like standing next to an F40PH that is standing at a station stop but is still running flat out.

The compressor rate (CV148 and CV149) concerns how often the air compressor kicks in during operation; a train moving over hilly terrain or starting or stopping frequently will have more frequent compressor operation as the engineer applies and releases the brakes.

The "air drier" is the device that dries the intake air prior to the compressor; since outside air contains moisture, the drier extracts this moisture so that the brake system is relatively dry.

As you watch a locomotive in operation, you periodically hear a loud "Phut" sound, which is the dryer expelling excess moisture; you will eventually spot the small pipe which points downward to the track as it shoots out a small cloud of water vapor that has been accumulated.


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