Cylinder design – The design activity has continued to provide manufacturing drawings for the workshop as well as a major effort to bring the design of the one-piece cylinder block to a stage where we are able to approach possible manufacturers. Our original idea was to make the block as a welded steel fabrication (a common practice in Germany and the United States in the final days of steam), however our sponsor, and Principal Sponsor for Tornado, William Cook Cast Products, has expressed an interest in looking into the possibility of producing it as a steel casting. A meeting is scheduled to take place shortly to progress this proposal.
The cylinder block has been extensively re-designed to overcome some of the known problems with No. 2001 Cock o’ the North, principally around separation of steam and exhaust passages within the cylinder block to reduce the tendency of the incoming live steam to transfer a significant amount of heat to the outgoing exhaust steam and to minimise the clearance volume in the cylinders. The clearance volume is the space left in the steam ports and the end of the cylinder when the piston is at the end of its stroke, and which was considered excessive on the original P2 poppet valve design. Both these features reduce the efficiency of the cylinders and give rise to high coal and water consumption. We are also having to address the overall width of the cylinders to meet modern clearances with platforms, and which needs to be reduced by 2″ to give us the widest route availability. This is being achieved mostly by using higher pressure steam (250 PSI compared with the original 220 PSI) which enables the cylinder diameter to be reduced from 21″ to 19.75″. The balance of 0.75″ reduction in width is being achieved by using steel instead of cast iron for the cylinder block which permits the cylinder walls to be thinner.
Key to CAD drawings:
Turquoise – welded fabrications from plate and machined from flame cut blanks
Brown – cast valve chests and steam passages
Magenta – cylinders and steam chests from tube
Note: Illustrations 1 and 2 are of the complete block, Illustration 3 has the smokebox saddle removed to enable the exhaust passages to be seen. The model still requires welding details.