Update 10 June – Northern and CAF engineers have now carried out temporary modifications to yaw dampers on their new trains, and a permanent solution will follow. Immediate good news is that most of the trains are now quickly and safely coming back into service. Northern’s recent (10 June) press statement is here, but if you want to know what the heck is a yaw damper, read on below!
Metal fatigue hits new trains (from our recent newsletter). At the end of May we understand about 30 of Northern’s CAF-built new trains were out of service including some of the “195s” used on our line. The problem is cracks on the brackets attaching a gadget called a yaw damper to the train body. A yaw damper is designed to stop the bogie wobbling from side to side as it rolls along. This transmits an oscillating force to the mounting and body, leading to metal fatigue, and ultimately cracking Lightweight aluminium used in construction is more prone to metal fatigue than steel. Yaw damper problems have also hit Hitachi high speed trains run by LNER, GWR and TransPennine Express, though it was cracks in jacking points that took those trains out of service recently. The issue is not new. British Rail had to redesign damper mountings on our familiar Class 158 units 30 years ago. It’s about designing components to reduce concentration of stress – avoiding sharp corners etc. Have modern train designers not learnt lessons?
Repairs will take time. It’s fortunate that with fewer passengers, for now, Northern can manage with shorter trains. As we write this most Calder Valley trains seem to be correct.
UPDATE: More at Train operator Northern issues update on Class 195 and 331 fault (railadvent.co.uk)