Watching the Rochelle webcam, I frequently hear the locos produce a"whirling" sound that rapidly increases in pitch and lasts about two seconds. It's especially common in eastbound UP locomotives immediately after clearing the diamonds - it sounds like a clutch or a fan being being engaged. My guess is that it might be some sort of cooling fan or pump being engaged to dissipate heat that collects in the engine, radiators, or traction motors following a throttle-down. It doesn't appear to be at least immediately associated with an increase in throttle setting. Any ideas???
What type of locomotives are involved?
GE locomotives make a sound sometimes described as a "whoop" that indicates the electrically driven air compressor starting.
I assume the locomotives brake approaching the diamonds and the air compressor then starts to refill the reservoirs.
The Australian Cv40-9i used to do that but they received new electronics in a major rebuild (which included new engines) and the compressor start is no longer obvious.
M636C
I'll second the compressor in the GE's.
Larry Resident Microferroequinologist (at least at my house) Everyone goes home; Safety begins with you My Opinion. Standard Disclaimers Apply. No Expiration Date Come ride the rails with me! There's one thing about humility - the moment you think you've got it, you've lost it...
M636CGE locomotives make a sound sometimes described as a "whoop" that indicates the electrically driven air compressor starting.
I've heard that often on the Rochelle webcam after the advent of sound, only on the GE's coming through. Come to think of it, it seems to have been heard more often on westbounds which would be yarding at G3. Glad that mystery has been cleared up for me, anyway.
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