One of the satisfying things about running this website is that it is read by people within the rail industry, who will respond with enthusiasm to technical questions. A case in point related to the picture above (by M.Lloyd Davies) which we included in the last issue with a question about the purpose of the orange box and cables. The following is complied from the several such replies received.
The bogies under these coaches are of the BT10 type designed by British Rail Engineering for the Mark 3 coaches in High Speed Train sets; for the latter, 125 mph capability was required. A loco-hauled version, Mark 3a, was also produced and had the same bogies. The conduit and junction box on the bogie is associated with the automatic Wheelslide Protection (WSP) system. The WSP system monitors the rotation of the axles and reduces the brake cylinder pressure on a particular axle if that axle starts to lock up which can lead to sliding which damages the wheels as well as causing problems stopping the train. This problem is particularly common under low-adhesion conditions such as during autumnal leaf fall.
As soon as normal rotation of the axle resumes, the brake cylinder pressure returns to that demanded by the driver. All of this happens in a split second and you can sometimes hear it happening (short pneumatic bursts) when sitting inside the vehicle. The system allows the driver to keep control of the train under low adhesion conditions and in theory prevents 'wheel flats' although this depends on the effectiveness of the WSP system in question - some are better than others - for instance, anybody who rides in class 323 electric trains in the autumn will appreciate this from the familiar 'bang' from under the coach for every revolution of the axle.
The flat circular enclosures on the axle ends contain toothed wheels bolted to the axles themselves and the cable entering the enclosure is for the sensor that detects the rotational speed of the wheels - by effectively counting the rate that the teeth are passing. The two electrical feeds that disappear across the top of the bogie frame go to the 'dump valves' that momentarily release the brakes, while the other electrical connection towards the vehicle body goes to the electronic control rack, which is the 'brain' of the system.
The six coaches recently refurbished for Arriva Trains Wales, now numbered 12176 to 12181, were originally Mark 3b First Class 'Pullman' carriages 11064 / 065 / 071 / 083 / 084 / 086 from a batch built in 1985, and as such were the ultimate development of the Mark 3 loco hauled vehicle as originally created. They were not actually Pullmans in the strict sense, but were marketed as luxury travel for business people. No supplement was charged over normal First Class, and they were included in most trains on their routes. 22 vehicles, 11073-94, were to replace the Mk2 Pullmans used on the 'Manchester Pullman' service and perpetuated the theme, first used on the Mk2 Pullmans in their later days, of naming after local heroes. 11083 was Kitty Wilkinson, 11084 William Roscoe, and 11086 Henry Doulton.
These Mark 3b vehicles have the most advanced WSP system, with one central WSP rack monitoring all four axles. It does this by comparing the frequency signals from the sensors on each axle - in an ideal world all the frequencies should be the same. The system can be programmed with the actual sizes of the wheels; a brand new full size wheelset will rotate more slowly than a fully-worn one. When the control rack detects that one or more axles is slowing down relative to other axles on the vehicle (because they are about to lock-up), it operates the dump valves.
Looking at Kitchen Buffet First 10249, this does not have the electrical cabling on the side of the bogie. This coach was converted from Mark 3a Restaurant Buffet car 10012, built in 1979, and has an earlier version of WSP fitted. On the axle-ends of the nearest bogie are small electrical generators and these feed a simple electronic unit that compares the voltage output from each axle - if the axle is about to lock-up the output falls and the dump valve is operated to release the brakes. This system is cruder than the Mark 3b version.
In British Rail days the Mark 3b Pullmans were always seen by maintenance staff as the 'cream of the fleet', as apart from the better WSP system and nicer interiors, they had more reliable Motor Alternators (part of the electrical supply for the vehicle) and the automatic vestibule doors were hardly any trouble when compared to the 1970s Mark 3 vehicles.
Many thanks to those who took the time to answer our question.
