Suppliers sought for cylinder block for No. 2007 "Prince of Wales"

In addition, and as part of the continued application of modern techniques in the design and development of the improved class P2, The A1 Steam Locomotive Trust has commissioned Frewer & Co Engineers Ltd of Dorking, Surrey to undertake a Computational Fluid Dynamics analysis of the inlet and exhaust steam passages of the cylinder block.

Despite the impact of COVID-19, progress on the construction of new Gresley class P2 ‘Mikado’ continues to move forward rapidly. The engine has reached the condition where it is recognisably a P2 and the structurally complete tender tank and tender wheelsets are now at Darlington Locomotive Works. Construction and assembly work continues on all fronts, including boiler, wheelsets, tender frames, heavy motion, pipework and electricals. Design work for the extensively modified and improved cylinder block is complete, with the focus now turned to the adaptation of the Lentz rotary cam poppet valve gear to further improve the original design.

The redesign of the cylinder block is one of the four principal areas of redesign identified by the project team before the launch of the project to build an improved Gresley class P2 in 2013:

• Develop improved pony truck and frame design using VAMPIRE® modelling data to confirm ride characteristics - completed
• Investigate and confirm valve gear to be fitted - choices were improved Lentz/Franklin, Walschaerts or British Caprotti; Lentz/Franklin was the final choice
• Investigate and reduce risk of crank axle failure apparent in the original design - completed
• Investigate and confirm design and method of construction of cylinders (cast versus fabrication) including Computational Fluid Dynamics (CFD) study.

As part of the redesign process, our team led by David Elliott, Director of P2 Engineering, took into consideration the following issues:

• The cylinders on the original Gresley class P2 were two inches wider overall than the Peppercorn class A1 cylinders
• Modern track on Network Rail has reduced clearance between track and station platforms
• Consequently, No. 2007 Prince of Wales must be no wider than No. 60163 Tornado to retain route clearance
• Using a 250psi boiler on No. 2007 Prince of Wales as fitted to No. 60163 Tornado, in place of the 220psi boiler fitted to the original class P2s, permits a reduction in cylinder diameter to 19¾in to maintain tractive effort
• Use of fabricated steel instead of cast iron will enable No. 2007 Prince of Wales’ cylinders to be no wider than those on No. 60163 Tornado
• Elimination of unsatisfactory features of the original design.

Upon the completion of the redesign work and the conversion of the design from a single monoblock casting of all three cylinders weighing around 5½ tons to a fabricated steel structure, David Elliott used a 3D printer to construct a 1/8 scale model of the new cylinder block to assist the selected manufacturer in its assembly.

Following initial dialogue with eight engineering companies, the Trust has issued a formal Request for Quotation (RFQ) to five organisations with all replies expected before the end of March 2021. All of the five companies have been issued with a 3D drawing of the modified cylinder block along with a Detailed Scope and Specification Document and associated manufacturing drawings.

Graeme Bunker-James, Commercial Director, A1SLT, commented: “When considering the award of this key contract our decision-making criteria will focus on potential suppliers demonstrating previous experience of projects of this scale and complexity, their ability to manufacture to the specified tolerances & surface finishes, their capacity to deliver the project within the required timescales, the value for money of the proposal and the long term financial stability of the business. Along with the valve gear, the placing of the order for the cylinder block in April 2021 will be the last major hurdle to overcome in the construction of No. 2007 Prince of Wales.”