The State of the Art of Steam Locomotive Design at the End of Its Development

On February 21, 1804 the first railroad journey ever took place near Merthyr Tydfil in Wales when Trevithick’s steam locomotive pulled a train along the tramway of the Penydarren Ironworks.  Within less than 30 years, Stephenson’s locomotive emerged as the basic design that would be common to virtually all steam locomotives built since then.  Yet after a rapid development which had led to very capable and efficient designs, steam locomotives had been largely retired from service in most countries around the mid-1970s.  The body of engineering and operational knowledge built up during that period of approximately 170 years may well be regarded as a cultural achievement and one that is now threatened by extinction by way of forgetting.

This paper – the result of decades of interest in and research regarding steam locomotives by its author – intends to document and discuss, in one place, the state of the art of steam locomotive design at its most advanced and hopes to make a small contribution to the slowing down the ‚tide of forgetting’.

Naturally, thus, the paper focuses on and examines those designs that were the last ones to be developed.  It, therefore, concentrates on locomotive types developed in the years after the end of WWII as those represent the most advanced state of steam locomotive design.

New steam locomotives or improved versions of previously designed steam locomotives were developed after WWII essentially only in the following countries:  China, Czechoslovakia, Germany (East and West), Great Britain, Poland, the Soviet Union and the United States of America.  Mostly due to what sources the author could access and the difficulties of overcoming some language barriers, the paper concentrates on the last steam locomotives designed in a subset of those countries, namely Czechoslovakia, Germany (East and West), Great Britain, Poland, and the United States and Canada.  The paper presents technical information and data on various of the post-WWII steam locomotive designs from these countries as obtained from numerous, referenced sources.  Where needed, data has been converted to make it consistent and comparable.

The paper is divided into eleven chapters with introductory and background material being covered in chapters 1 through 3.  In particular, chapter 3.1 provides a concise description of the key aspects of the Stephenson-style steam locomotive design that was so prevalent since the 1830s.

Chapters 4 through 7 discuss in considerable detail each of the main components of a steam locomotive – the boiler (chapter 4), the steam engine and drive mechanism (chapter 5) , the chassis or frame (chapter 6) and the running gear (chapter 7).  In each case, those main components are further broken down into their sub-components.  And in the case of each such sub-component, its review begins with an introductory section followed by a discussion of the state of the art of both the European and the U.S. designs which often, though not always, differed considerably.

Wherever the respective information was available to the author, not only functional aspects are described but also the materials and construction methods used as well.  Furthermore – unlike many other publications on steam locomotive design – the various design solutions are not only described but critically analyzed from an engineer’s point of view, thus highlighting not only their advantages but their limitations as well.  These discussions at times reveal interesting contrasts between the design principles/requirements put forth by the various national or private railway companies for the locomotive designs under their purview as well as how circumstances facing a particular railroad system (e.g. cost of coal vs. cost of labor; quality of the railroad tracks, etc.) may have influenced those requirements and, ultimately, design decisions.

Throughout chapters 4 through 7, situations are discussed where the competition between two or more design solutions were not resolved before the end of the development of the steam locomotive (e.g. various approaches to the axle bearings).  Cases where no truly satisfactory solution to a given engineering challenge were ever arrived at (e.g. feedwater heating and water treatment) are also described.  Additionally, cases where the Stephenson-style steam locomotive ran into its natural limits (e.g. the maximum reasonable size of the grate area) are pointed out.

Chapter 8 addresses performance aspects and documents the maximum power and tractive force that steam locomotives were capable of delivering in their most advanced state. Naturally, indicated power and tractive force are normalized to total locomotive and tender weight or adhesive weight.  Scatters of data points in graphs are made more comprehensible by trend lines which, in turn, represent the state of the art reached at the end of the steam locomotive’s development.

Operational, utilization and maintenance considerations are discussed in chapter 9 where 9.1 in particular discusses typical daily mileage and typical rates of availability.

The paper is essentially concluded in Chapter 10 with a summary of limitations and reasons that led to the replacement of the steam locomotive by Diesel and electric locomotives soon after the end of WWII.  Basically, and as previously alluded to in passages of the preceding chapters, the performance and efficiency of the Stephenson-style steam locomotive could not be increased any further and the considerable environmental impact of the steam locomotive could not be completely ignored any longer.

Chapter 11, finally, contains a number of appendices, including a detailed discussion of the Baker valve gear that employs photos taken of a little model built for this very purpose and a list of references (chapter 11.9) which are referred to throughout the paper.