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Thread: engine at end of train

  1. #1
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    Default engine at end of train

    I saw a train of empty coal hoppers with a dash 9 in front and one at the other end of the train why would they put an engine at the end and not behind the lead unit?

  2. #2
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    Default RE: engine at end of train

    Sometimes they put one on the back to help the front one, if you put 1 in the front and one in the back it will help the train out

    JT

  3. #3
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    Default RE: engine at end of train

    Thats called DPU (Distributed Power Unit). It is controlled from the head end unit. It does exactly the same thing as lead unit. It is usually the standard on all coal train. It is usually two up front and one on the back or two up front and two on the back. It is done to help keep the train up to speed, and to keep it from pulling apart.

  4. #4
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    Default RE: engine at end of train

    Also to add on to this, the reason they put another loco in the middle is to keep the slack stretched out between the whole train and to keep the brake pressure up on the train in the winter times when the temperature falls and the air contracts so it takes longer for the brake cylinder to recharge.

  5. #5
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    Default RE: engine at end of train

    Hi Brad,
    You probably don't need more than one unit to actually move the empty hoppers, although they create a lot of drag as speed increases. A single CW44-9 could likely pull the entire group at 25 mph. Now the unit at the end may be there for several reasons. First, it was probably there when the loaded train departed. By having some of the power on the back, you reduce thew strain on the couplers near the front of a loaded train. When the train dumps, it does not disassemble, it just dumps the coal sort of like in a conveyor action, probably going around a big circle, or it dumps to the side and departs in the opposite direction, with the trailing unit becoming the lead.
    Another reason to have a unit pushing, is that the empty hoppers are quite light. With a string of say 105 empty hoppers, the train will be very long. When you go around curves, the tendency will be for a long light train to straighten out the curve, much like putting a string in a loop, and pulling on one end. This can derail the train. By having forces carefully pushing and pulling, the train can keep the cars bunched, and there will be less slack running in on grades. If the rear locomotive pushes too hard, then that can be just as bad or worse. That is why the CW44AC-CTE became popular on these types of trains, it can provide better distributed power on long trains, and not push too hard on a light train.
    Bob

  6. #6
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    Default RE: engine at end of train

    Do these DPU's have a crew in them? I once saw a mixed NS freight go by with a couple dash9's up front and at the end of the train were two former Conrail SD40-2s, and it looked as if these units had a crew in them.

  7. #7
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    Default RE: engine at end of train

    No.

  8. #8
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    Default RE: engine at end of train

    >No.

    He most likely saw a helper crew, not actually a DPU.

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