Development
On the InterCity 225 (IC225) sets operating on the East Coast Main Line (ECML) the Mark 4 DVTs and locomotives operate in push-pull formation utilising a time-division multiplexer to send control signals along specially screened cables which run the length of the train. The locomotives usually face away from London, only being changed occasionally in rare circumstances.
On the original Mark 3 DVTs, which operated on the West Coast Main Line (WCML), the intention was to use the RCH jumpers to carry the signals therefore allowing the same cables to be used for lighting and the public address system, as well as driver-guard signalling. However this proved to be very troublesome in service and eventually the rakes of coaches on the WCML were re-wired with specially screened cables exclusively for the TDM system.
In addition to the driver's cab, some DVTs have luggage and cycle storage space and a guard's office.
When a train is operated by a DVT, the control signals are encoded and multiplexed onto the cables by the TDM equipment in the DVT. At the locomotive, these signals are demultiplexed by the TDM equipment, and the signals are used to control the locomotive. The air braking system is operated directly from whichever cab the driver is driving from. If the TDM fails and cannot be reconfigured, the train may still operate, but if the DVT is leading, it will be necessary to uncouple the locomotive and attach it to the front of the train.
The DVT was developed from the Mark 2 DBSO, but unlike its predecessor, it was built specifically for this purpose. The original DVTs were designed to be used with Mark 2 D, E & F and Mark 3 coaches, and the second design with Mark 4 coaches, which have a narrower profile. This enables it to be converted to tilting operation if required in the future.
Mark 3 DVTs can be seen in service in the UK today with EWS, with Greater Anglia Mainline services and occasionally with Virgin West Coast, powered by Class 90 locomotives. During its operation, Wrexham & Shropshire utilised Mark 3 DVTs on its services between London and Wrexham powered by Class 67 locomotives. The Mark 4 DVT is operated by East Coast and powered by Class 91s. They were also powered by the unique Class 89 Co-Co locomotive which once operated on the same route but is now preserved.
Read more about this topic: Driving Van Trailer
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