New and old ZB cylinders

On the left is one of the new fabricated cylinders for the ZBs showing the larger and more direct passageways. Alongside is one of the original cylinders.

New Front End for BVR ZBs

In traffic the Bure Valley Railway's class of ZB locomotives were found to have high fuel and water consumption and as passenger loadings continued to rise over a number of seasons it became apparent that the locomotives were slow to accelerate the increasingly heavy summer loads and could not maintain full line speed on gradients.

Rebuilding two of the locomotives offered the opportunity to improve the performance by redesigning the front end to incorporate new cylinders, valve gear modifications and Lempor exhaust systems. Ian Gaylor undertook the design programme which included all necessary drawings, calculations and computer modelling of the valve gear and exhaust systems. All the new parts were made by Alan Keef Ltd who also rebuilt No. 9 while the Bure Valley Railway rebuilt No. 6 at their Aylsham workshops. The results were assessed by dynamometer trials of No. 9 compared to the unrebuilt members of the class, Nos. 7 & 8. Fuel consumption was found to have been reduced by 25% and power output more than doubled making timekeeping easy with heavy trains and reducing operating costs.

Steam Loco Design's Ian Gaylor tells the full story of the ZBs' transformation in this six part article.