DPU |
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Distributed Power Unit. A DPU is basically a radio controlled locomotive that can be positioned within or at the end of the train (signal levels determine this). The leading loco controls this remote unit. Bothj lead loco and the DPU are specially equipped for this.
The purpose of the DPU is to ease the load on the train. While locos at the front could pull the train, there were a lot of coupler breakages on the drawbar. So by putting a powered loco way back in the train it eased the coupler load. And that was efficiant. Both the lead loco and the DPU can handle a MU loco attached for more power. The MU = muliple Unit is basically a hard wired remote control that most diesel locos have had for decades. Another advantage is braking. when a train needs to stop or slow, the lead engine reduces air pressure in the main air line on the train. this takes time to reduce pressure from the front to the rear. With a DPU it can be commanded to reduce pressure at the same time alead loco does that stops the train quicker. Another key advantage. This has resulted in longer trains being able to be run without issues. It also means train can be split up - and made up at yards quicker. 
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