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Coupling Codes


Coupling Codes

Red Triangle

West Riding Derby Lightweights
Class 127

Yellow Diamond

Other Derby Lightweights
79xxx series Met Cams
Class 129

White Circle

Class 126

Orange Star

Class 125

Blue Square

All other vehicles

The first vehicles delivered, the West Riding Derby Lightweights had what became the Red Triangle coupling code, which enabled them to work in multiples of up to eight power cars. Jumpers were at waist level. For the next sets delivered, the remaining Derby Lightweights and the Met-Cam Lightweights, a change had been made from hydraulic transmission with a Yellow Diamond code. Jumpers were again at waist level. When not in use on the outer ends, the cables could be removed for storage inside the vehicles.

The system evolved for the introduction of Swindon’s first Inter City vehicles, described as White Circle. These vehicles were distinct in having no through air pipe between vehicles, so each power car depended on producing it’s own air. These vehicles were unique in having no jumpers or sockets on the outer ends of the ‘leading’ type power cars, and jumpers from the 'intermediate' power cars were kept in the guards van. Jumpers were located on the buffer beam, an operating change as it was found that most coupling/uncoupling was done at track rather than platform level.

The next vehicles, Classes 105 and 114 which arrived at the same time, were the first cars to have what became the standard coupling code, Blue Square. However there were some teething problems with this and there was temporarily a diagonal stripe added to the blue square on the 114s, a code that was also used on a Class 116 set. Class 114s were also unusual for Blue Square sets in that the jumper sockets are mounted rotated 180 degree from other classes.

All future vehicles, with the exception of three classes, were built to Blue Square.

The Class 125s (and their prototype 50000/56000) were the only vehicles to receive the Orange Star coupling code, meaning they couldn’t work with any other sets, an important factor in their early withdrawal.

The second batch of Class 126 vehicles delivered in 1958 were also given the White Circle system, although this was actually incompatible with the original White Circles. The 1956 vehicles were based on Yellow Circle with no through air pipe, while the 1959 ones were based on Blue Square with no through air pipe. Modifications had to be done to allow the sets to work together. On the second batch jumpers were fitted to the front of the ‘leading’ type vehicles. Apart from the lack of through air pipe, another contributing factor in these vehicles receiving their own code was their buckeye couplings and Pullman gangways.

Although all passenger carrying Cravens vehicles were Blue Square, the three Class 129 DMUs were fitted with the Yellow Diamond system as they were built to work with the Yellow Diamond Derby Lightweights.

Whilst built with a Blue Square control system the Class 127s (and a few remaining Class 113s?) were reclassified in 1969 as Red Triangle. When driving from the hydraulic set the driver had to consider the needs of a mechanical set if coupled in multiple, as if the gears are not changed properly then overheating and a fire would occur. After a serious incident of this nature they were reclassified to prevent it happening again. All the Red Triangle Derby Lightweights had been withdrawn by this time, and the Class 127s were in no way compatible with them, as the change was in name only.

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