Uboats dropping load with throttle changes

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Spur44
Posts: 9
Joined: Fri Apr 06, 2018 8:47 am

Uboats dropping load with throttle changes

Post by Spur44 » Mon Dec 23, 2019 1:36 pm

So the title says it all. I've read about this phenomenon several times, on various forums, but I don't think I've ever seen it fully explained or described. So was this something related to the U series, across the board. Was it with every single throttle change and when it did drop load how much of a change was it? Did it drop load completely or just a little?

Thanks in advance for the info!

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Wayside
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Re: Uboats dropping load with throttle changes

Post by Wayside » Wed Dec 25, 2019 1:59 pm

In my experience (operating freight trains for PC/CR for roughly 15 years) this was a phenomenon that plagued the U series units. Compared to the EMD products (35 series and later) the load control of the U-boats was atrocious. Early U25/28 series were the worst, as I recall, in that they would sometimes load tremendously in the lower throttle positions, especially as speed was reduced such as when attempting to glide to a smooth stop when power (stretch) braking. This power surge could be enough to break a knuckle if one wasn't careful.

And yes, when accelerating, every throttle notch would often cause a dramatic drop in load. What ensued next was a slow spool-up of the turbo (and a cloud of black smoke) and redevelopment of power for the notch selected. EMD had developed a system that produced a specific horsepower output for each throttle position. It took years for GE to figure out how to do the same thing.

You might get the impression that I didn't like early GEs. And you would be right in that regard.
We don't know what we don't know.

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