RAILROAD GUYS: What is this sound and one other Q

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So I was watching an old locomotive documentary and of all the things I could have noticed...... during one of the segments the helper Amtrack engine made this electronic StarWars-ish type of sound "vruuuu-uuaah" like some generator spinning up. But What IS it, why does it do that, etc. I am curious as heck and am not a railroad guy... yet.


Loco video


Also, during the video I was amazed at the rotating mass of the drive wheels on the old steam loco and how those connecting rods flew around. Can you tell me about how they are balanced? I know that their is offsetting weight inherent in the wheels but how to the actually go about balancing them and what kind of tolerances are there?
 
Originally Posted By: skyactiv
The video is over an hour long. Can you tell us where to start the video at?


Oh sorry I cut it in at the moment listen at 25:09... just a few seconds after the cut in.
 
Originally Posted By: Boomer
There is also a diesel engine in that train.


Yes, I mention that in the original post, that there is an Amtrack helper engine and that is the engine from whence I heard the spin-up sound of electronics or something at minute 25:09.
 
Sounds like a cooling fan turned on. I'm guessing the car behind the loco is a back-up diesel electric that is running and one of the cooling fans engaged. Hear it all the time on the locomotives going by my place.
 
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Nope-air compressor, kicks in when the pressure in the system drops to operate the air brakes. Probably on the Amtrak Genesis helper engine that is behind the steam engine. Cool video!
 
That sound is the air compressor starting up.

On GE locomotives, the compressor only runs as needed. It is run by an electrical motor that runs of the electrical power generated by the diesel electric generator. Thus it is noticeable when it spools up.

On an EMD, the compressor is run off a shaft from the diesel engine that has valving that either sends air to the compressor or vents it. The compressor is always running in this setup - though it often isn't loading the system up.
 
I agree with bullwinkle and MNgopher- compressor kicking in. I see and hear dozens of them everyday passing the shop. Usually at least 3 at varying times are parked for a spell nearby too (generally a helper or distributed power unit) at the tail, as the lead engine is over a mile away next to a crossing changing crews.
 
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