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About "Standard steam locomotives"

The website is designed to give a rapidly accessible summary of the basic specification data of various steam locomotives worldwide, on gauges from 15 inches to seven foot (and a monorail). Since it is not feasible to give a comprehensive coverage of all types, the emphasis is on "standard" steam locomotives, those types that were built in the largest quantities, or that shared major components (such as boilers) with standard types. Locomotives of especial interest are often included as well. The choice is limited by the availability of reliable data. New railways are gradually being added, and earlier tables improved.

1. What is in the tables?

The table columns, in order, give the following data:

  • the class (or representative number in the series) - including links to photographs or small drawings in some cases
  • the wheel or axle arrangement
  • the diameter of the driving wheels
  • the diameter and stroke of the cylinders
  • the boiler pressure
  • the adhesive weight (in working order)
  • the engine weight (in working order)
  • the grate area (for oil-firing: firebox cross-section)
  • the total evaporative heating surface
  • the superheater surface (where applicable)
  • additional remarks (e.g. type of articulation or compounding, cross-reference to other tables, popular name of the class, type and tractive effort of geared locomotives, etc).
Two systems of units are used: Imperial, with wheel arrangements on the Whyte pattern (e.g.
Mikado as 2-8-2), or Metric, with axle arrangements on the central European system (Mikado as 1'D1'). Since the cylinder dimensions, driving wheel diameters, and boiler pressures are nominal, the choice of units for each table is generally made so that these figures come out even for the majority of types listed there. Note that the weights in all the tables are given in metric tons (2,205lb). For each given cylinder size, the default option for the number of cylinders of that size is two. Thus the Austrian 108 class Atlantic, a four-cylinder compound, is listed as
mm, while the 208 class, a two-cylinder cross-compound, is listed as
mm. The 308 class, a two-cylinder simple, is listed as
mm. In compound locomotives, the high pressure cylinder dimension (usually diameter) is given first, then the corresponding low pressure dimension preceded by a slash. If both cylinder dimensions differ, the high and low pressure dimensions are separated by a colon. If a simple locomotive (such as the UP 4-12-2) has cylinders of varying dimensions, these dimensions are separated by a colon.

2. What isn't in the tables?

Fitting one class per line means that there is only room for the primary, basic data. It is not possible to list secondary data such as tractive effort, maximum speed, horsepower, etc. However, some quick rules of thumb can provide estimates of these derived quantities in terms of the table entries:

  • The truly available tractive effort will not generally exceed one fourth of the adhesive weight. (The nominal tractive effort of a simple locomotive is usually calculated as one half the total cylinder volume times the boiler pressure, divided by the driving wheel diameter, and modified by a "fudge factor" in the range from 95% to 108%.)
  • The maximum axle load is not given, but a close lower estimate is generally obtained on dividing the adhesive weight by the number of coupled axles. (The PKP TKr55 is an exception, having its maximum axle load on the front pony truck.)
  • The maximum speed in miles per hour is generally approximated by the driving wheel diameter in inches (or 40 times the diameter in metres). For the maximum speed in kilometres per hour, take one-sixteenth of the driving wheel diameter in millimetres.
  • The maximum sustainable horsepower of an advanced steam locomotive is about 80% - 100% of its evaporative heating surface in square feet, or 8 to 10 times its evaporative heating surface in square metres.  These factors should be halved for older locomotives with slide valves and no superheater, and further reduced for small narrow-gauge locomotives.

3. How can you compare data from different tables?

Clicking on the "open second copy" field of the index page should open the index page in a second browser window.  Tables may then be selected from each index page, and the two windows arranged one above the other.

4. What was the source of the data?

The information has been collated from diagram books, manufacturer's catalogues, published books, and journals such as "Railway Age," "Engineering," etc.  I would also like to acknowledge contributions from Ab Baird, Larry Baxter, Reg Carter (1934 - 2007), S. Damus, A.E. "Dusty" Durrant (1929 - 1999), Robin Gibbons, Dr Malcolm Hardy-Randall, Barry Heath, Hugh C. Hughes (191? - 1998), Ian Hughes, Berne Ketchum, Ichiro Kondo, Steve Llanso, Joe Lloyd, Stephen Low, Mark Lundquist, Bruce Maxwell, Gerry Nichols, Kurt Niederer, R. Ramaer, N.D.H. Smith (1926 - 2003), Wolfgang Staiger, Allen Stanley, Jim Todd, Ralph Wallio, Malcolm Wilton-Jones, and Jiří Woitsch, as well as the B&O Museum (Baltimore, MD), Colorado Railroad Museum (Golden, CO), James H. Andrew Railroad Museum (Boone, IA), Museum of Science and Industry (Manchester), and Muzeum Kolejnictwa (Warsaw). If you are able to fill any of the gaps in the tables, please visit the Post Office.

5. How reliable are the data?

Except for cylinder stroke, all the other measurements listed are subject to variation of as much as several percent. Boiler pressures depend on the setting of the safety valves, and with pop valves there is a difference of several pounds per square inch between the opening and closing pressures. Cylinders and driving wheel tyres are subject to wear and repair, altering the diameter. Since the weights listed are those "in working order," there may be variation of up to several tons depending on how high the water is being carried in the boiler, or how much the water and fuel supplies of tank engines have been depleted. Adjustments to the suspension may trade off between the adhesive and non-adhesive weights. The heating surfaces may have been calculated on the Anglo-Saxon "steam side" system or the continental "smoke side" system. (The former system overstates the evaporative surface and understates the superheating surface by up to 25% relative to the latter.) Whichever system is used, the surfaces also vary as the boiler is brought up to working pressure. Within large classes, there may be substantial variation between different members. If a locomotive is in service for a long period of time, its specifications may change as a result of reboilering or other factors. Taking all these effects into account, there are often still discrepancies amongst different sources. Finally, the operation of data entry is not completely reliable, although such errors may gradually be identified and eliminated as the tables are used.

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