Steam locomotive

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A steam locomotive is a locomotive powered by a steam engine. The term usually refers to its use on railways, but can also refer to a "road locomotive" such as a traction engine or steamroller.

Steam locomotives dominated rail traction from the mid 19th century until the mid 20th century, after which they were superseded by diesel and electric locomotives.

Contents 1 Origins 2 Basic form 2.1 Boiler 2.2 Steam circuit 2.3 Chassis 2.4 Running gear 2.5 Fuel and water 2.6 Crew 3 Fittings and appliances 3.1 Superheating 3.1.1 Introduction 3.1.2 The Reasoning Behind Superheating 3.1.2.1 What is superheating? 3.1.2.2 Dryness Fraction 3.1.2.3 Demand For Increasing Haulage Capacity of Locomotives 3.1.2.4 Research leading to the development of Superheating 3.1.2.5 The First Superheaters 3.1.2.6 Superiority of superheated steam locomotives 3.1.2.7 Degrees of superheat 3.1.2.8 Characteristics of Superheated Steam 3.1.3 Applications of Superheated Steam to Locomotives 3.1.3.1 Balancing disadvantages and advantages of Superheating 3.1.4 Conclusion to Superheating 3.2 Steam pumps and injectors 3.3 Boiler lagging 3.4 Pressure gauge 3.5 Stokers 3.6 Feedwater heaters 3.7 Condensers and water re-supply 3.8 Braking 3.9 Lubrication 3.10 Buffers 3.11 Pilots 3.12 Headlights 3.13 Bells and whistles 3.14 Automatic Train Control 3.15 Booster engines 4 Variations 4.1 Cylinders 4.2 Cab forward 4.3 Steam turbines 4.4 Valve gear 4.5 Compounding 4.6 Articulated and Duplex types 4.7 Hybrid power 5 Manufacture 5.1 United States 5.2 United Kingdom 5.3 Australia 6 Categorisation 7 Performance 7.1 Measurement 7.2 Relation to wheel arrangement 8 The end of steam 8.1 United States 8.2 United Kingdom 8.3 South Korea 8.4 Other countries 9 Hopes of revival 10 References 11 See also 12 External links 13 Books on steam locomotives

[edit] Origins

See also: History of rail transport, Category:Early steam locomotives

The earliest railways employed horses to draw carts along railed tracks.

As the development of steam engines progressed through the 1700s, various attempts were made to apply them to road and railway use.^[1] The first attempts were made in Great Britain; the earliest steam rail locomotive was built in 1804 by Richard Trevithick and Andrew Vivian. It ran with mixed success on the narrow gauge "Penydarren tramroad" at Merthyr Tydfil in Wales.^[1]. Then followed the successful twin cylinder locomotives built by Matthew Murray for the edge railed Middleton Railway in 1812. These early efforts culminated in 1829 with the Rainhill Trials and the opening of the Liverpool and Manchester Railway a year later making exclusive use of steam power for both passenger and freight trains.

Inspired by British success, the United States started developing steam locomotives in 1829 with the Baltimore and Ohio Railroad's Tom Thumb. This was the first locomotive to run in America, although it was intended as a demonstration of the potential of steam traction, rather than as a revenue-earning locomotive. The first successful steam railway in the US was the South Carolina Railroad whose inaugural train ran in December 1830 hauled by the Best Friend of Charleston. Many of the earliest locomotives for American railroads were imported from England, including the Stourbridge Lion and the John Bull, but a domestic locomotive manufacturing industry was quickly established, with locomotives like the DeWitt Clinton being built in the 1830s.^[2]

[edit] Basic form

[edit] Boiler

The typical steam locomotive employs a horizontal fire-tube boiler partially filled with water. A firebox, its walls and roof constantly surrounded, by water is incorporated generally to the rear of the boiler when the locomotive is travelling chimney-first; this is where a combustible is burnt, the heat generated thereby being transferred to the water in the boiler in order to make the steam, that constitutes working medium. The combustion gases flow from the firebox into a bundle of parallel tubes, also surrounded by water, which continue to transfer heat to the water At the front of the boiler is the smokebox, a chamber where the combustion gases are mixed with the jet of exhaust steam, the whole being ejected into a chimney (US: "smoke stack") voiding into the outside air.

[edit] Steam circuit

The generated steam is stored in the steam space above the water in the partially-filled boiler. Its working pressure is limited by spring-loaded safety valves. It is then collected either in a perforated tube fitted above the water level or from a dome that often houses the regulator valve or throttle the purpose of which is to control the the amount of steam leaving the boiler. The steam then either travels directly along and down a steam pipe to the engine part or may have first to pass into the wet header of a superheater the role of which is to eliminate water droplets suspended in the "saturated steam", the state in which it leaves the boiler. On leaving the superheater, the "dried" steam exits the dry header of the superheater and passing down a steam pipe enters the steam chests adjacent to the cylinders of a reciprocating engine. Inside each steam chest is a sliding valve that distributes the steam via ports that connect the steam chest to the ends of the cylinder space. The role of the valves is twofold: admission of each fresh dose of steam and exhaust of the used steam once it has done its work.

The cylinders are double acting, with steam admitted to each side of the piston in turn. In a two-cylinder locomotive, one cylinder is located on each side of the locomotive. The cranks are set 90° out of phase with each other. During a full rotation of the driving wheel, steam provides four power strokes per revolution; that is to say each cylinder receives two injections of steam. The first stroke is to the front of the piston and the second stroke to the rear of the piston; hence two working strokes. Consequently two deliveries of steam onto each piston face in two cylinders generates a full revolution of the driving wheel. The driving wheels are connected on each side by coupling rods (US: "connecting rods") to transmit power from the main driver to the other wheels. At the two "dead centres", when the connecting rod is on the same axis as the crankpin on the driving wheel, it will be noted that no turning force can be applied. If the locomotive were to come to rest in this position it would be impossible for it to move off again, so the cylinders and crankpins are arranged such that the dead centres occur out of phase with each other. This precaution is unnecessary on most other reciprocating engines (such as an internal combustion engine) which are never expected to start from rest under their own power, and employ a flywheel to overcome the dead centres.

Each piston transmits power directly through a connecting rod (US: main rod) and a crankpin (US: wristpin) on the driving wheel (US "main driver) or to a crank on a driving axle. The movement of the valves in the steam chest is controlled through a set of rods and linkages called the valve gear, driven from the driving axle or else from the crankpin; the valve gear includes devices that combine the roles of reversing the engine and adjusting valve travel and the timing of of the admission and exhaust events. The cut-off point determines the the moment when the valve obturates a steam port, "cutting off" admission steam and thus determining the proportion of the stroke, during which steam is admitted into the cylinder; for example a 50% cut-off admits steam for half the stroke of the piston. The remainder of the stroke is driven by the expansive force of the steam. Careful use of cut-off provides economical use of steam and, in turn, reduces fuel and water consumption. The reversing lever (US: Johnson bar), or screw-reverser, (if so equipped) which controls the cut-off therefore performs a similar function to a gearshift in an automobile.

Exhaust steam is directed to the chimney, via a nozzle called a blastpipe. This is where the gases are combined and the combustion gases drawn through the boiler and grate by the pumping action of of the exhaust steam. The blast of exhausted steam produces the familiar "chuffing" sound of the steam locomotive. The fact that the draft depends on the on exhaust pressure means that power delivery and power generation are automatically self-adjusting.

[edit] Chassis

With European locomotives, the chassis is the principle structure onto which the boiler is mounted and which incorporates the various elements of the running gear.The chassis consists of two mainframes kept apart and square by spacers and “buffer beams”. For many years, in America practice , the boiler was the main structural element, with built-up bar frames, ‘’smokebox saddle/cylinder’’ structure and drag beam integrated therein; but from the late 1920s with the introduction of ‘’superpower’’, the ‘’cast-steel locomotive bed’’ became the norm, incorporating frames, spring hangers, motion brackets, smokebox saddle and cylinder blocks incorporated into a single complex, sturdy but heavy casting. André Chapelon developed a similar welded structure with around 30% saving in weight for the still-born 2-10-4 locomotives the construction of which was begun then abandoned in 1946.

[edit] Running gear

This includes the brake gear, wheel sets, axleboxes, springing and the "motion" that includes connecting rods and valve gear. The transmission of the power from the pistons to the rails and the behaviour of the locomotive as a vehicle, able to negotiate curves, points and irregularities in the track are issues of paramount importance. Because reciprocating power has to be directly applied to the rail from 0 rpm upwards, this poses unique problems of ‘’adhesion’’ of the driving wheels to the smooth rail surface. Adhesive weight is the portion of the locomotive’s weight bearing on the driving wheels. This is made more effective if pair of driving wheel is able to make the most of its ‘’axle load’’ i.e. its individual share of the adhesive weight. Locomotives with ‘’compensating levers’’ connecting the ends of plate springs have often been deemed a complication but locomotives fitted with them have usually been less prone to loss of traction due to wheel-slip.

Locomotives with total adhesion, i.e. where all the wheels are coupled together, generally lack stability at speed. This makes desirable the inclusion of unpowered carrying wheels mounted on two-wheeled trucks or 4-wheeled bogies centred by springs that help to guide the locomotive through curves. These usually take the weight of the cylinders in front or of the firebox at the rear end when the width of this exceeds that of the mainframes. For multiple coupled wheels on a rigid chassis a variety of systems for controlled side-play exist.

[edit] Fuel and water

Generally, the largest locomotives are permanently coupled to a tender that carries the water and fuel. Alternatively, locomotives working shorter distances carry the fuel in a bunker, and the water in tanks mounted on the engine, the latter placed either alongside the boiler or on top of it; these are called tank engines".

The fuel source used depends on what is economically available locally to the railway. In the UK and parts of Europe, a plentiful supply of coal made this the obvious choice from the earliest days of the steam engine. German, Russian, Australian and British railways experimented using coal dust to fire locomotives. Wood-burning engines were found in rural and logging districts in Europe and in the U.S.A. well into the 19th century. Bagasse, a waste by-product of the refining process, was burned in sugar cane farming operations. In the USA, the ready availability of oil made this a popular steam locomotive fuel; the Southern Pacific, for example, went directly from wood to oil.^{[citation needed]} equipment. In Victoria, Australia after World War II, many steam locomotives were converted to heavy oil firing.

A number of tourist lines and heritage locomotives in Switzerland, Argentina and and Australia have been using light diesel-type oil.^[3].

Water was supplied at stopping places and loco depots from a dedicated water tower connected to water cranes or gantries. In the UK and the USA, water troughs (US track pans) were provided on some main lines to allow locomotives to replenish their water supply without stopping. This was achieved by using a 'water scoop' fitted under the tender or the rear water tank in the case of a large tank engine; the fireman remotely lowered the scoop into the trough, the speed of the engine forced the water up into the tank, and the scoop was raised again once it was full.

Water is an essential element in the operation of a steam locomotive; because as Swengel argued, 'it has the highest specific heat of any common substance; that is more thermal energy is stored by heating water to a given temperature than would be stored by heating an equal mass of steel or copper to the same temperature. In addition, the property of vapourising (forming steam) stores additional energy without increasing the temperature...water is a very satisfactory medium for converting thermal energy of fuel into mechanical energy.'

Said Swengel, 'at low temperature and relatively low boiler outputs' good water and regular boiler washout was an acceptable practise, even though such maintenance was high. As steam pressures increased, however, a problem of 'foaming' or 'priming' developed in the boiler, wherein dissolved solids in the water formed 'tough skined bubbles' inside the boiler, which in turn were carried into the steam pipes and could blow off the cylinder heads. To overcome the problem, hot mineral concentrated water was deliberately wasted (blowing down) from the boiler from time to time. Higher steam pressures required more blowing down of water out of the boiler. Oxygen generated by boiling water attacks the boiler and with increased steam pressures the rate of rust (iron oxide) generated inside the boiler increases. One way to help overcome the problem was water treatment. Swengel suggested that the problems around water, contributed to the interest in electrification of railways. ^[4]

In the 1970s L.D. Porta developed a sophisticated heavy duty chemical water treatment that not only keeps the inside of the boiler clean and prevents corrosion, but modifies the foam in such a way as to form a compact "blanket" on the water surface that filters the steam as it is produced, keeping it pure and preventing carry-over into the cylinders of water and suspended abrasive matter.

[edit] Crew

A locomotive is controlled from the backhead of the firebox and the crew is usually protected by a cab A crew of at least two people is normally required to operate a steam locomotive. One, the driver (US engineer), is responsible for controlling the locomotive and the other, the boilerman or fireman, is responsible for the fire, steam pressure, and water.^[5]

See also Category:locomotive parts

[edit] Fittings and appliances

All locomotives are fitted with a variety of appliances. Some of these relate directly to the operation of the steam engine; while others are for signalling, train control, or other purposes. In the United States the Federal Railroad Administration mandated the use of certain appliances over the years in response to safety issues. The most typical appliances are as follows:

[edit] Superheating

[edit] Introduction

Aspects of superheating as applied to steam locomotives could fill entire libraries, but here is a summary. In the 19th century most steam locomotives used saturated steam. Archibald Sturrock, a locomotive superintendent of a British railway, put the design philosophy of the day in this way: "The power of a locomotive is its capacity to boil water." To make a locomotive more powerful, it was seen to be a simple matter of making the boiler larger and larger. This "bigger is better" treatment was applied especially to the fireboxes which were made wider and longer, thus necessitating some form of mechanical stoking. However, it was realised fairly early on in this process that contemporary steam locomotive development was heading up a blind alleyway. The boiler could only be made so big, as it had to fit under the bridges, past the stations & signals and through the tunnels. Long boilers tend to be overly heavy, or have an unacceptable overhang on the locomotive.

Successful researchers realised this in the late 1800s, and continuing all the way through the 1900s, and even into the 2000s, they pursued another line of investigation, one of the most successful ever applied to any steam installation, be it a locomotive, a ship or a power station: superheating. Swengel (1967:122) said that 'no single development ever equalled the superheater as a means of removing limitations from steam locomotive design'.

[edit] The Reasoning Behind Superheating

[edit] What is superheating?

In any steam boiler, a certain amount of heat energy is applied to the water to make it boil. The steam thus produced is at the same temperature as the water below it. This is called saturated steam. If the steam is taken away from the boiler, in a pipe, and then further heat is applied to that steam, the steam can rise above the temperature of the water in the boiler. This heated-above-the-boiler-temperature steam is called "superheated".

Saturated steam has some of the water in it, either as suspended droplets carried over from the boiler water, or as condensation from the steam being cooled slightly when it leaves the boiler and comes in contact with as-yet-unwarmed engine parts. This amount of water droplets carried within the steam flow is called "dryness fraction"

[edit] Dryness Fraction

Saturated steam has a given amount of water droplets, or condensate, in it. If the steam is almost all water droplets, then it is said to have a low dryness fraction (say, 1%). If it has almost no condensate, then it is deemed to have a high dryness fraction. Dryness fraction is indicated in several ways, as a percentage (10% dryness fraction means that the steam is 10% pure steam and 90% water droplets) or as a fraction A dryness fraction of ½ means that ½ of the steam is pure steam and the other ½ is water droplets. Dryness fraction is also given as a unitless number: 0.5 is the same as ½.

It should be noted that the drier the steam, the better the performance of the locomotive or steam plant in general, since steam has expansive powers and water droplets do not. Supplying lots of water droplets into a steam cylinder would make it unable to work, or make it work very poorly. One pound of saturated steam at 200 p.s.i. occupies 2.134 cubic feet of volume. When admitted to the cylinders the water (condensation) content of this steam is usually about 7%.

Steam domes were provided on some locomotives in an attempt to take the steam from the highest point available, and thus have the driest steam available. The taller the steam dome, the drier the steam, or so says the theory. But as we saw in the introduction to this section, given that the boiler has to fit under the bridges, the bigger the boiler, the smaller the steam dome. Some locomotives had no steam dome whatsoever.

The Dryness Fraction of the supplied steam is crucial to the efficiency of a steam plant. A low dryness fraction equals a very low efficiency. Superheated steam has a 100% dryness fraction.

Although water in its gaseous form (i.e., steam) can be compressed, liquid water cannot be. As a result, any liquid water trapped in the steam cylinders can cause great problems, especially if the cylinder has piston valves. If the cylinder has slide valves, they can "open" to allow the trapped water to escape. The higher the dryness fraction, the lower the amount of trapped water that will be in the cylinders. Trapped water that cannot escape from the cylinder can cause the engine to "hydraulically lock", thus bending the connecting rods, breaking the cylinder casting, shearing the piston retaining mechanism or destroying other vital components. Such a locomotive is in need of urgent major repairs. Avoiding trapped condensation water was thus of the highest priority for the drivers of the locomotives. Prior to superheating, and given the use of piston valves, a steam locomotive could not handle more than 7% water (from whatever source) in its cylinders, without sustaining significant damage.

[edit] Demand For Increasing Haulage Capacity of Locomotives

It was obvious by the 1880s that boilers could not go much larger without major expense of raising all of the bridges and re-boring all of the tunnels, yet the demand for more powerful locomotives was present on every continent. Thus, prior to superheating locomotive development had almost reached its practical capacity with saturated steam. This need for increasing power and tractive effort was especially true in the United States as the rail transport industry had just embarked on a project to vastly increase the carrying capacity of their railroads in concert with the breathtaking expansion of the needs of the oil industry. It was the increasing use of the products of the Oil Industry that paid for this, ironically a trend which later saw the eclipsing of the rail industry in the United States as the primary means of land transport.

At first, compounding was used to try and provide the increased power, by increasing efficiency in the use of steam. These locomotives went under many forms, the best known of which was the Mallets, a compounding and articulation system named after Anatole Mallet. He was a Swiss national working in France, who devised his system for narrow gauge locomotives to increase locomotive hauling capacity (and thus line capacity). Mallet's type of articulation was taken to its logical extremes in the US, which saw some gigantic locomotives culminating in the truly gargantuan Virginian Railroad's 800 class 2-10-10-2s which had their low-pressure cylinders at 48 inches in diameter (1.219 m) and the less-than-entirely-successful "triplexes" of the Erie railroad and the Virginian railroad.

[edit] Research leading to the development of Superheating

With the obvious need to provide more powerful locomotives, and the boilers now reaching their size limits, and the cylinders getting larger and larger (with all of the problems associated with balancing), research revealed that increased heating surface in the boiler was insufficient by itself^{[citation needed]}. The free gas area, given as the sum of the cross-sectional areas of all of the fire tubes in the boiler, must be at least 16% of the grate area, and preferably a lot more. Research proved that the best arrangement was for a tube whose length was 100 times its internal diameter, for the best efficiency. Too small, and the gas flow is impeded. Impeded gas flow means the locomotive must pump more steam up the chimney to make the gas flow through the tubes, thus working the locomotive harder to produce the same steam. This greater pumping effort means increased back-pressure, which in turn reduces the power available for traction. Too large a tube and the flue gasses will form a cool "skin" along the surface of the tube which will allow most of the heat of the fire to shoot up the middle of the tube and not do any useful heat transference before being blasted out of the chimney. However, any boiler designed on the above idea of length being 100 times the diameter will be too long, too heavy and (likely) too expensive.

It was Dr Wilhelm Schmidt of Kassel, Germany, who undertook the follow-up research to the heat-transfer problems within boilers and it was he who developed the successful superheater.

[edit] The First Superheaters

Whilst the principle of superheating had been known for a very long time, no practical way had been found to make use of it. In the 1890s, Dr Schmidt began trials of his design of superheater, which was a form of "flame tube" superheater - a single, very large boiler tube of 17.5 inches (440 mm) across had a large number of steam pipes placed within it. These steam pipes were the superheater elements. The flame tube thus allowed the full force of the fire's burning to impinge upon the superheater elements, thus providing the greatest heat transference possible. A trial on a steam locomotive was arranged and two locomotives were so fitted, an S3 and a P4 of the Prussian railways. The S3 started it's trials on the 13th of April of 1898, and completing them in the same month. Results were very encouraging, although there were distortions in the flame-tube.

Two more designs were then produced; a type of smoke-box "superheater" which provided a very low superheat and a fire-tube superheater, in which mid-sized tubes were placed in the boiler and then the superheater elements placed within those. The first type (the one in the smoke box) turned out to be less than successful, and was eventually superseded by the second, which became standard on virtually all large steam locomotives until the very end of steam.

After the superheater became widely used, the normal method for superheating was set. This is to pipe the steam from the dome to a wet header in the smokebox; sometimes the throttle or regulator is in the dome, sometimes in this header. The steam is then directed through a set of smaller "U" shaped tubes running inside enlarged boiler fire tubes, and thence into a second dry header, where the throttle could be located in the case of some advanced locomotives. The now-superheated steam then passes on through to the cylinders and after doing useful work pushing the piston back and forth, exhausts up the chimney.

Superheating is also fitted to stationary steam plant and to marine steam engines.

[edit] Superiority of superheated steam locomotives

Dr Schmidt's road tests of his superheater designs showed that there would be a saving of 12% at least in coal consumption, with a possible 20% or more if high degrees of superheat were applied^{[citation needed]}. Similar reductions in water consumption were also noted. The Tractive Effort of the locomotives also seemed to be increased, especially the continuous tractive effort when the locomotive was running at or near top speed. In short, it meant that at the same time as increasing the loads being hauled, the locomotives ran the same runs using less fuel and water.

To quote from T. Grime, in the Proceedings of the Institute of Locomotive Engineering:

When steam is superheated to a final temperature of 650°~700 °F (340 °C~370 °C), economies of 15 to 25% in fuel and 25 to 35% in water are attainable. With 300 °F (150 °C) superheat, the water and coal consumption may be as low as 16 pounds per indicated horsepower hour (9.7 kg/kWh) and 1.8 pounds per indicated horsepower hour (1.1 kg/kWh). In general, the steam economy is roughly proportional to the specific volumes of saturated and superheated steam at the pressure of generation. [Thus] the operating range of any given [steam] engine is increased; this is of especial benefit to tank engines and to all engines working in areas where fuel is expensive or water is scarce. The proportion of time spent in taking water and fuel, or alternatively, the frequency with which these operations are necessary, is therefore reduced.

[edit] Degrees of superheat

Given that superheating produces an increase in efficiency of 10-15% for an increase in temperature of 100 to 150 F° (55 to 85 C°), some locomotives have a greater degree of superheat applied. In a traditional steam locomotive, sometimes higher temperatures did not offer proportionally greater efficiencies. The reasons for this were studied extensively by André Chapelon in his work, which showed why this was the case. His rebuilt locomotives made excellent use of very high superheat, and were the more efficient because of it^[6]. His student, namely Livio Dante Porta, took up Chapelon's work and extended it. The degree of superheat applied to Livio Dante Porta's locomotives would have been considered "prolific" even bordering on the "insanely high" by the designers of traditional steam locomotives. Superheated locomotives were sometimes fitted with pyrometers to indicate the steam temperature which, towards the end of the steam era, was typically around 600 °F (315 °C).

To quote from 'Steam Locomotive Design: Data and Formulae"^[7]

there is an unfortunate lack of uniformity in the practical application of the descriptions given to steam in its various states. The acceptance of the following is, however, fairly general:- Any apparatus giving a superheat of 10° - 20 °F (5.5 °C - 11.5 °C) is termed a steam drier.

• A low degree of superheat is one giving a superheat of 50°F to 100°F;
• A moderate degree implies a superheat of about 100 °F-200 °F;
• A high degree superheat is that in excess of 200 °F.

Livio Dante Porta started his superheat at 450 °C (842 °F), which would probably come in under the general heading of "excessive" in the above scheme of things and his locomotives were very successful with a greatly increased efficiency. This was due to many other changes that Livio Dante Porta realised had to be made in order to take advantage of the increased superheat. In one locomotive, he increased the superheat by the simple expedient of hammering tapered wooden dowels into the smokebox end of the non-superheater boiler tubes thus stopping any flue gasses from passing into them. This reduced to zero the heating surface of the non-superheater flues, while vastly increasing the heat and flow through the superheater elements. The locomotive so treated was noted for it's increased overall efficiency.

[edit] Characteristics of Superheated Steam

To quote from 'Steam Locomotive Design: Data and Formulae" ^[8]:

Compared with saturated steam, superheated steam:-

1. Possesses a larger volume and greater total heat value per unit of mass
2. More nearly approaches the condition of a perfect gas. It is therefore more fluid; hence, frictional resistance to flow is reduced and, consequently, a higher flow velocity attained under given conditions [this has been disputed, but it's part of the original quote so I have left it as is]
3. Of itself possesses no lubricating qualities whatsoever, and is intensely cutting in action. This explains the necessity for the adoption of cast iron, or, preferably, steel for piping, together with the other measures previously mentioned [better lubrication is needed because the steam temperature is higher]
4. Does not increase the load starting capacity of any given locomotive, but provides a considerable increase in the power output when running
5. Gives a more rapidly falling expansion curve on the indicator diagram, but coincidentally the back pressure is reduced and the compression curve improved, to such an extent that the mean effective pressure is not impaired and is, in fact, higher at piston speeds of 1,000 feet (300 m) per minute and over
6. Has a lower heat conductivity [which means the cooling near the walls of the piping does not propagate as fast across the steam volume as in saturated steam - the middle of the flow remains hotter, longer]
7. Must lose all superheat before condensation can commence
8. Enables the water to be carried at a lower level in the boiler as the evaporation [in the boiler] is not so rapid and high rates of combustion are unnecessary [thus reducing fuel wastage]. Incidentally, this procedure also conduces to a higher dryness fraction, and therefore tends to raise the degree of superheat

[edit] Applications of Superheated Steam to Locomotives

The first applications of the superheater were to stationary practice, then marine practice, then the locomotives in Germany, namely the S3 class 4-4-0s from the class build of 1899 onwards. The S3 class appeared from 1893 onwards, thus the earlier ones had no superheater; this was fitted later on when the locomotives were given major overhauls. In Europe and Britain, and especially France, the use of the superheater spread rapidly.

In the United States, the first wide-spread use of the superheater seems to have been in the D16sb class 4-4-0s of the Pennsylvania Railroad in 1905. The better known E3sd 4-4-2's of the Pennsylvania Railroad were superheated and these locomotives formed the trial for the better-known K28's and K4s' Pacifics (4-6-2's)

The last known large American main-line steam locomotive built new without a superheater seems to have been the F15 4-6-2's of the Chesapeake and Ohio Railroad of 1902. They were all superheated following rebuilds during the 1920s, and some seemed to have survived in that form until the dieselisation efforts of the 1950s. After these locomotives, it would seem all new built locomotives for mainline passenger or express use had superheaters fitted from new.

On freight engines, this was the era of the Drag Freight, a reference to the practice of attaching as many wagons behind the engine as could be dragged up the steepest of grades. This was slow, plodding, tough and very high powered haulage, which was seen as not benefiting from superheating. Thus large saturated steam locomotives for freight duties appeared as late as the early 1920s. After that date, the superheater was deemed to be proven technology and thus the more recently built freight engines were slowly superheated as major overhauls fell due. Freight engines built new after the mid 1920s appear to have been superheated from the start, especially those locomotives which hauled the newly-appeared fast freight. The Era of Drag Freight was ending as competition with the motor vehicle became more apparent and rail began to lose out on the more time-sensitive freight to the highways. It should be noted that the way the rail companies had built up their systems to handle these enormous, slow freight trains was one of the reasons they were simply not agile enough to counter the threat from road transport.

[edit] Balancing disadvantages and advantages of Superheating

• Superheated steam is a most erosive substance. This means the parts exposed to it are likely to wear out faster, unless made of higher tensile substances. While this meant the superheater and all of the piping and valving needs to be made of more expensive materials, the savings in fuel and water are such to more than compensate for the increased costs. Also, the better the materials, the lower the maintenance costs.

• It also requires special lubrication because of the increased heat. Given that the problem of adequate lubrication was only resolutely tackled right at the end of steam, the use of superheated steam meant this problem, which could be more-or-less ignored on saturated steam engines, became acute.

• Related to the above, saturated steam will provide lubrication for moving parts; superheated steam will not.

• The fitting of any new piece of equipment, such as a superheater, will require more maintenance. However the superheater will reduce the maintenance costs of the boiler, because the boiler is less stressed.

On balance, the superheater is a highly desirable device, except where the use of the locomotive is such that the superheater would not get the time to warm up (say, a shunting or switching locomotive). It will reduce costs, fuel, water and maintenance. It increases power and range of the locomotives.

[edit] Conclusion to Superheating

The benefits of superheating are many.

One of these is in the reduction of this heat loss through condensation.^[9] There are references to an increase in starting tractive effort due to superheating, however such was not strictly true. The early practice following the initial introduction of superheating involved lowering the boiler pressure (thus lowering boiler maintenance costs) while increasing the cylinder size to obtain to achieve the same tractive effort. At the same time the removal of many small tubes and replacing them with larger diameter flues, to hold the superheaters, lessened the amount of evaporate surface, compared with the old saturated boiler. While this limited the capacity of the locomotive's boiler, the locomotive itself had a higher power, due to the presence of the superheater. Some superheater-fitted engines did not perform as well as was expected, entirely due to a misunderstanding of the needs of a superheated engine^[10] By the mid-1920s, designers understood that superheating, large fire-spaces and a good boiler capacity were the key to successful locomotives.^[10]

Many locomotives had a superheater fitted, without these additional desiderata, and the superheater was subsequently blamed for the lack of performance. It was the study of these failures and the application of the lessons learnt in the design work of André Chapelon, sometimes ignored in the United States, that showed how to use the superheater effectively. These modifications included the use of very large pipes to conduct the steam to where it was needed; overly large valves with a long lap and a locomotive exhaust system that could handle the greatly increased through-put of steam. Chapelon's final rebuilds in 1935 had unbelievable power-to-weight ratios of around 42 draw bar horse power per ton. To give a salient example, if a New York Central Niagara 4-8-4 had had a similar power-to-weight ratio to that of André Chapelon's last set of rebuilds, the New York Central's locomotives would have been capable of producing over 17,000 rail horse power.

Even today, André Chapelon's lesson has not been well learnt, if at all. It should be noted that the best a modern-day diesel locomotive can achieve (and at 214% the initial purchase price of a steam locomotive) is a power to weight ratio of 22.84 draw-bar horse power per ton.

---

[edit] Steam pumps and injectors

Water must be forced into the boiler, to replace that which is exhausted after delivering a working stroke to the pistons. Early engines used pumps driven by the motion of the pistons. Later steam injectors replaced the pump, while some engines use turbopumps. Standard practice evolved to use two independent systems for feeding water to the boiler. Vertical glass tubes, known as water gauges or water glasses, show the level of water in the boiler.

[edit] Boiler lagging

Large amounts of heat are wasted if a boiler is not insulated. Early locomotives used shaped wooden battens fitted lengthways along the boiler barrel and held in place by metal bands. Improved insulating methods included: applying a thick paste containing a porous mineral, such as kieselgur; fixing "mattresses" of stitched asbestos cloth stuffed with asbestos fibre around (but on separators so as not quite to touch) the boiler; attaching shaped blocks of insulating compound. The most common modern day material is glass wool, or wrappings of aluminium foil. The installation is covered by a close fitted sheet-metal casing.^[11] Effective lagging is particularly important for fireless locomotives.

[edit] Pressure gauge

The earliest locomotives did not show the pressure of steam in the boiler, but it was possible to estimate this by the state of the safety valve. However, the promoters of the Rainhill trials urged that each contender have a proper mechanism for reading the boiler pressure and Stephenson devised a nine-foot vertical tube of mercury with a sight-glass at the top, mounted alongside the chimney, for the Rocket. The Bourdon tube gauge, in which the pressure straightens an oval-section, coiled tube of brass or bronze connected to a pointer, was not introduced until the 1850s. This is the device used today.^[12] Some locomotives have an additional pressure gauge in the steam chest. This helps the driver avoid wheel-slip at startup, by warning if the regulator opening is too great.

[edit] Stokers

A factor that limits locomotive performance is the rate at which fuel is fed into the fire. In the early 20th century some locomotives became so large, that the fireman could not shovel coal fast enough.^[11] In the United States, various steam-powered mechanical stokers became standard equipment and were adopted and used elsewhere including Australia and South Africa.

[edit] Feedwater heaters

Introducing cold water into a boiler reduces power, and from the 1920s a variety of heaters extracted residual heat from the exhaust and raised the temperature of the feed water. An example of the pre-heater is found on the Franco-Crosti boiler.

The use of live steam and exhaust steam injectors also assists in the pre-heating of boiler feed water, though there is no efficiency advantage to live steam injectors. Such pre-heating also reduces the thermal shock that a boiler might experience when cold water is introduced directly.

[edit] Condensers and water re-supply

Steam locomotives consume vast quantities of water, and supplying this was a constant logistical problem. In some desert areas, condensing engines were devised. These engines had huge radiators in their tenders and instead of exhausting steam out of the funnel it was captured and passed back to the tender and condensed. The cylinder lubricating oil was removed from the exhausted steam to avoid a phenomenon known as priming, a condition caused by foaming in the boiler which would allow water to be carried into the cylinders causing damage because of its incompressibility. The most notable engines employing condensers (Class 25C) worked across the Karoo desert of South Africa, from the 1950 until the 1980s.

Some British and American locomotives were equipped with scoops which collected water from "water troughs" (US: "track pans") while in motion, thus avoiding stops for water. In the US, small communities often did not have refilling facilities. During the early days of railroading, the crew simply stopped next to a stream and filled the tender using leather buckets. This was known as “jerking water” and led to the term "jerkwater towns" (meaning a small town, a term which today is considered derisive). ^[13] In Australia and South Africa, locomotives in drier regions operated with large oversized tenders and some even had an additional water wagon, sometimes called a "canteen" or in Australia (particularly in New South Wales) a "water gin".

Steam locomotives working on underground railways (such as London's Metropolitan Railway) were fitted with condensing apparatus for a different, but obvious, reason. These were still being used between King's Cross and Moorgate into the 1950s.

[edit] Braking

Locomotives have their own braking system, independent from the rest of the train. Locomotive brakes employ large shoes which press against the driving wheel treads. With the advent of air brakes, a separate system also allowed the driver to control the brakes on all cars. These systems require steam-powered pumps, which are mounted on the side of the boiler or on the smokebox front. Such systems operated in the United States, Canada and Australia.

An alternative to the air brake is the vacuum brake. Where vacuum brakes are used, a steam-operated ejector is mounted on the engine instead of the air pump. A secondary ejector or crosshead vacuum pump is used to maintain the vacuum in the system. Vacuum systems existed on British, Indian and South African rail networks.

Steam locomotives are nearly always fitted with sandboxes from which sand can be delivered to the rails to improve traction and braking in wet weather. On American locomotives the sandboxes, or sand domes, are usually mounted on top of the boiler. In Britain, the limited loading gauge precludes this, so the sandboxes are mounted just above, or just below, the running plate.

[edit] Lubrication

The pistons and valves on the earliest locomotives were lubricated by the enginemen dropping a lump of tallow down the blast pipe.^[14]

As speeds and distances increased, mechanisms were developed that injected thick mineral oil into the steam supply. The first, a displacement lubricator, mounted in the cab, uses a controlled stream of steam condensing into a sealed container of oil. Water from the condensed steam displaces the oil into pipes. The apparatus is usually fitted with sight-glasses to confirm the rate of supply. A later method uses a mechanical pump worked from one of the crossheads. In both cases, the supply of oil is proportional to the speed of the locomotive.

Lubricating the frame components (axle bearings, horn blocks and bogie pivots) depends on capillary action: trimmings of worsted yarn are trailed from oil reservoirs into pipes leading to the respective component.^[15] The rate of oil supplied is controlled by the size of the bundle of yarn and not the speed of the locomotive, so it is necessary to remove the trimmings (which are mounted on wire) when stationary. However, at regular stops (such as a terminating station platform) oil finding its way onto the track can still be a problem.

Crank pin and crosshead bearings carry small cup-shaped reservoirs for oil. These have feed pipes to the bearing surface that start above the normal fill level, or are kept closed by a loose-fitting pin, so that only when the locomotive is in motion does oil enter. In United Kingdom practice the cups are closed with simple corks, but these have a piece of porous cane pushed through them to admit air. It is customary for a small capsule of pungent oil (aniseed or garlic) to be incorporated in the bearing metal to warn if the lubrication fails and excess heating or wear occurs.

[edit] Buffers

In British practice, the locomotive usually had buffers at each end to absorb compressive loads ("buffets"^[16]). The tensional load of drawing the train (draft force) is carried by the coupling system. Together these control slack between the locomotive and train, absorb minor impacts, and provide a bearing point for pushing movements.

In American practice all of the forces between the locomotive and cars are handled through the coupler and its associated draft gear, which allows some limited slack movement. Small dimples called "poling pockets" at the front and rear corners of the locomotive allowed cars to be pushed on an adjacent track using a pole braced between the locomotive and the cars.

[edit] Pilots

In the United States, South Africa and Australia, locomotives had a pilot at the front end. Plow-shaped, and called cow catchers, they were quite large and were designed to remove obstacles from the track such as cattle, bison, other animals or tree limbs. Though unable to "catch" stray cattle these distinctive items remained on locomotives in those countries until the end of steam. Switching engines usually replaced the pilot with small steps. In places like Victoria, Australia, the cow catchers became a trade mark of that state's engines (Dee:1998).

[edit] Headlights

When night operations began, railway companies in some countries equipped their locomotives with lights to allow the driver to see what lay ahead of the train or to enable others to see the locomotive. Originally headlights were oil or acetylene lamps, but when electric lights became available in the late 1880s, they quickly replaced the older types.

Britain used low intensity oil lamps and were not intended to allow the driver to see the way ahead (locomotive drivers were expected to have sufficient route knowledge) but were used to indicate the class of a train by their position on the front of the locomotive. Four lamp irons were provided: one below the chimney and three evenly spaced across the top of the buffer beam. The exception to this was the Southern Railway and its constituents, who added two lamp irons one each side of the smokebox, and the arrangement of lamps (or in daylight white circular plates) told railway staff the origin and destination of the train.

In some countries heritage steam operation continues on the national network. Some railway authorities have mandated powerful headlights on at all times, including during daylight. This was to further inform the public or track workers of any active trains.

[edit] Bells and whistles

Main article: Train whistle

Locomotives used bells and steam whistles from earliest days. In the United States and Canada bells warned of a train in motion. In Britain, where all lines are by law fenced throughout,^[17] bells were only a requirement on railways running on a road (i.e. not fenced off), for example a tramway along the side of the road or in a dockyard. Consequently only a minority of locomotives in the UK carried bells. Whistles are used to signal personnel and give warnings. Depending on the terrain the locomotive was being used in the whistle could be designed for long distance warning of impending arrival, or more for localised use.

Early bells and whistles were sounded through pull-string cords and levers. As the steam era approached the 1950s, automatic air-operated bells were made use of on locomotives such as the Challenger (steam locomotive) and Big Boy.

[edit] Automatic Train Control

From early in the twentieth century operating companies in such countries as Germany and Britain began to fit locomotives with in-cab signalling which automatically applied the brakes when a signal was passed at "caution". In Britain these became mandatory in 1956.

[edit] Booster engines

In the United States and Australia the trailing truck was often equipped with an auxiliary steam engine which provided extra power for starting. This booster engine was set to cut out automatically at a certain speed. On the narrow gauged New Zealand railway system, six Kb 4-8-4 locomotives had boosters; the only 3 ft 6 in (metre gauge) engines in the world to have such equipment.

[edit] Variations

Numerous variations to the simple locomotive occurred as railways attempted to develop more powerful, more efficient and fast steam locomotives.

[edit] Cylinders

Some locomotives received extra cylinders and experiments combined two locomotives in one (e.g. the Mallet and Garratt locomotives). Some locomotives carried their cylinders vertically alongside the boiler and drove the wheels through a system of shafts and gears (e.g. the Shay locomotive; see "geared steam locomotive").

From about 1930, most new British express passenger locomotives were 4-6-0 or 4-6-2 types with three or four cylinders. Examples include:

• GWR 4073 Class, four-cylinder 4-6-0
• LNER Class A1/A3, three-cylinder 4-6-2

[edit] Cab forward

In the United States on the Southern Pacific Railroad a series of cab forward locomotives had the cab and the firebox at the front of the locomotive and the tender behind the smokebox, so that the engine appeared to run backwards. This was only possible by using oil-firing. Southern Pacific selected this design to provide smoke-free breathing for the locomotive's engineer as they went through the SP's numerous mountain tunnels and snow sheds. Another variation was the Camelback locomotive with the cab half-way along the boiler.

[edit] Steam turbines

Steam turbines were one of the experiments in improving the operation and efficiency of steam locomotives. Experiments with steam turbines using direct-drive and electrical transmissions, in different countries, proved mostly unsuccessful.^[11] The LMS also built Turbomotive, a largely successful attempt to prove the efficiency of steam turbines.^[11] Had it not been for the outbreak of WW2, more may have been built. The Turbomotive ran from 1935-49, when it was rebuilt into a conventional locomotive because replacement of many parts was required, an uneconomical proposition for a 'one-off' locomotive. In the United States the Union Pacific, Chesapeake and Ohio, and Norfolk & Western railways all built turbine-electric locomotives. The Pennsylvania Railroad (PRR) also built turbine locos but with a direct-drive gearbox. However, all designs failed due to dust, vibration, design flaws, or inefficiency below speed. The last one in service was the N&W's being retired in January 1958.

[edit] Valve gear

Numerous technological advances improved the steam engine. Early locomotives used simple valve gear that gave full power in either forward or reverse.^[12] Soon Stephenson valve gear allowed the driver to control cutoff; this was largely superseded by Walschaerts valve gear and similar patterns. Early locomotive designs using slide valves and outside admission were easy to construct, but inefficient and prone to wear.^[12] Eventually, slide valves were superseded by inside admission piston valves, though there were attempts to apply poppet valves (common by then on stationary engines) in the 20th century. Stephenson valve gear was generally placed within the frame and was difficult to access for maintenance; later patterns applied outside the frame, were readily visible and maintained.

[edit] Compounding

From 1876, compound locomotives came on the scene, which used the engine's steam twice. There were many compound locomotives especially where long periods of continuous efforts were needed. Compounding was an essential ingredient of the quantum leap in power achieved by André Chapelon's rebuilds from 1929. A common application was to articulated locomotive, the most common being that of Anatole Mallet in which the high pressure stage was attached directly to the boiler frame; in front of this was pivoted a low pressure engine on its own frame, taking the the exhaust from the rear engine. ^[18]

[edit] Articulated and Duplex types

Articulation itself proved very popular, and there were numerous variations, both compound and simple. Duplex locomotives with two engines in one rigid frame were also tried, but were not notably successful.^{[citation needed]}

[edit] Hybrid power

Main article: Steam diesel hybrid locomotive

‎

Mixed power locomotives, utilising steam and diesel propulsion, have been produced in Russia, Britain and Italy.

[edit] Manufacture

[edit] United States

With the notable exception of the USRA standard locomotives, set during World War 1, in the United States, steam locomotive manufacture was always customised. Railroads ordered locomotives tailored to their specific requirements, though basic similarities were always present. Railroads developed specific characteristics; for example, the Pennsylvania Railroad had a preference for the Belpaire firebox,^[19] while the Delaware and Hudson Railroad was famous for its elaborately flanged smokestacks.^{[citation needed]} In the United States, specialised manufacturers constructed locomotives for all rail companies, although all railroads had shops capable of heavy repairs and some railroads (for example the Norfolk and Western Railway) constructed locomotives in their own shops. Companies Manufacturing locomotives in the US included Baldwin Locomotive Works, American Locomotive Works (ALCO), and others. It was not uncommon for an entire group of locomotives to be sold from one railroad to another.^{[citation needed]}

Steam locomotives required regular service and overhaul (often at government-regulated intervals). Many alterations occurred during overhauls. New appliances were added, unsatisfactory features removed, cylinders improved or replaced. Any part of the locomotive, including boilers were replaced or upgraded. On the Baltimore and Ohio Railroad two 2-10-2 locomotives were dismantled; the boilers were placed onto two new Class T 4-8-2 locomotives and the residue wheel machinery made a pair of Class U 0-10-0 switchers with new boilers. Union Pacific's fleet of 3 cylinder 4-10-2 engines were converted into two cylinder engines in 1942, because of high maintenance problems.

[edit] United Kingdom

Before the 1923 Grouping, the picture in the UK was mixed. The larger railway companies built locomotives in their own workshops but the smaller ones and industrial concerns ordered them from outside builders. A large market for outside builders was abroad because of the home-build policy exercised by the main railway companies.

Between 1923 and 1947, the "Big Four" railway companies (the Great Western Railway, the London, Midland and Scottish Railway, the London and North Eastern Railway and the Southern Railway) all built most of their own locomotives. Generally speaking, they only bought locomotives from outside builders when their own works were fully occupied. From 1948, British Railways adopted the same policy and continued to build new steam locomotives until 1960 (the last being named Evening Star).

Some independent manufacturers produced steam locomotives for a few more years, the last British-built industrial steam locomotive being constructed by Hunslet in 1971. Since then, a few specialised manufacturers have continued to produce small locomotives for narrow gauge and miniature railways, but as the prime market for these is the tourist and heritage railway sector, the demand for such locomotives is limited.

[edit] Australia

In Australia, Clyde Engineering of Sydney and also the Eveleigh Workshops built steam locomotives for the New South Wales Government Railways. These include the C38 class 4-6-2, the first five were build at Clyde with streamlining, the other 25 locomotives were built at Eveleigh (13) in Sydney, and Cardiff Workshops (12) near Newcastle. In Queensland, steam locomotives were locally constructed by Walkers. Similarly the South Australian state government railways also manufactured steam locomotives locally at Islington in Adelaide. The Victorian Railways constructed most of their locomotives at their Newport Workshops and Bendigo while in the early days locomotives were built in Ballarat. Locomotives constructed at the Newport shops ranged from the nA class 2-6-2T built for the narrow gauge, up to the H class 4-8-4, the largest conventional locomotive ever to operate in Australia, which weighed 260 tons. However, the title of largest locomotive in Australia goes to the 263 ton NSWGR AD60 class 4-8-4+4-8-4 Garratt (Oberg:1975), which were built by Beyer-Peacock in the United Kingdom.

[edit] Categorisation

Steam locomotives are categorised by their wheel arrangement. The two dominant systems for this are the Whyte notation and UIC classification.

The Whyte notation, used in most English speaking and Commonwealth countries, represents each set of wheels with a number. Different arrangements were given names which usually reflect the first usage of the arrangement; for instance the "Santa Fe" type (2-10-2) is so called because the first examples were built for the Atchison, Topeka and Santa Fe Railroad. These names were informally given and varied according to region and even politics.

The UIC classification is used mostly in European countries apart from the United Kingdom. It designates consecutive pairs of wheels (informally "axles") with a number for non-driving wheels and a capital letter for driving wheels (A=1, B=2 etc). So a Whyte 4-6-2 designation would be an equivalent to a 2-C-1 UIC designation.

On many railroads, locomotives were organised into classes. These broadly represented locomotives which could be substituted for each other in service, but most commonly a class represented a single design. As a rule classes were assigned some sort of code, generally based on the wheel arrangement. Classes also commonly acquired nicknames representing notable (and sometimes uncomplimentary) features of the locomotives.^{[citation needed]}

[edit] Performance

[edit] Measurement

In the steam locomotive era, two measures of locomotive performance were generally applied. At first, locomotives were rated by tractive effort This can be roughly calculated by multiplying the total piston area by 85% of the boiler pressure (a rule of thumb reflecting the slightly lower pressure in the steam chest above the cylinder) and dividing by the ratio of the driver diameter over the piston stroke. However, the precise formula is:

Tractive Effort is defined as the average force developed during one revolution of the driving wheels at the rail head.^[10] This is expressed as:

.

where d is bore of cylinder (diameter) in inches, s is cylinder stroke, in inches, P is boiler pressure in pound per square inch, D is driving wheel diameter in inches, c is the effective cutoff.^[20]

It is critical to appreciate the use of the term 'average', as not all effort is constant during the one revolution of the drivers for at some points of the cycle only one piston is exerting turning moment and at other points both pistons are working. Not all boilers deliver full power at starting and also the tractive effort decreases as the rotating speed increases.^[10]

Tractive effort is a measure of the heaviest load a locomotive can start or haul at very low speed over the ruling grade in a given territory.^[10]

However, as the pressure grew to run faster freight and heavier passenger trains, tractive effort was seen to be an inadequate measure of performance because it did not take into account speed.

Therefore in the 20th century, locomotives began to be rated by power output. A variety of calculations and formulas were applied, but in general railroads used dynamometer cars to measure tractive force at speed in actual road testing. This measure was termed drawbar horsepower in the United States and remained the standard measure of performance to the end of mainline usage.^{[citation needed]}

British railway companies have been reluctant to disclose figures for drawbar horsepower and have usually relied on continuous tractive effort instead.

[edit] Relation to wheel arrangement

Whyte classification is connected to locomotive performance, but through a somewhat circuitous path. Given adequate proportions of the rest of the locomotive, power output is determined by the size of the fire, and for a bituminous coal-fuelled locomotive, this is determined by the grate area. Modern non-compound locomotives are typically able to produce about 40 drawbar horsepower per square foot of grate. Tractive force, as noted earlier, is largely determined by the boiler pressure, the cylinder proportions, and the size of the drivers. However, it is also limited by the weight on the drivers (termed adhesive weight), which needs to be at least four times the tractive effort.^[11]

The weight of the locomotive is roughly proportional to the power output; the number of axles required is determined by this weight divided by the axleload limit for the trackage where the locomotive is to be used. The number of drivers is derived from the adhesive weight in the same manner, leaving the remaining axles to be accounted for by the leading and trailing bogies.^[11] Passenger locomotives conventionally had two-axle leading bogies for better guidance at speed; on the other hand, the vast increase of the grate and firebox in the 20th century meant that trailing truck was called upon to provide its support.

As a rule, "shunting engines" (US "switching engines") omitted leading and trailing trucks, both to maximise tractive effort available and to reduce wheelbase. Speed was unimportant; making the smallest engine (and therefore smallest fuel consumption) for the tractive effort paramount. Drivers were small and usually supported the firebox as well as the main section of the boiler. Helper engines tended to follow the principles of switchers, except that the wheelbase limitation did not apply. Therefore helpers tended to multiply the number of drivers, leading eventually to the Mallet type with its many driven wheels. These tended to acquire leading and then trailing trucks as guidance of the engine became more of an issue.

As locomotive types began to diverge in the late 1800s, freight engines at first emphasised tractive effort, whereas passenger engines emphasised speed. Freight locomotives multiplied axles, kept the leading truck to a single axle, and grew a trailing truck as the firebox expanded and could no longer fit between or above the drivers. Passenger locomotives had leading bogies with two axles, fewer axles, and very large driving wheels in order to limit the speed at which the reciprocating parts had to move.

In the 1920s the focus in the United States turned to horsepower, epitomised by the "super power" concept promoted by the Lima Locomotive Works. Freight trains were to run faster; passenger locomotives needed to pull heavier loads at speed. In essence, the grate and firebox expanded without changes to the remainder of the locomotive, forcing the trailing truck to grow a second axle. Freight 2-8-2s became 2-8-4s while 2-10-2s became 2-10-4s. Similarly, passenger 4-6-2s became 4-6-4s. In the United States this led to a convergence on the dual-purpose 4-8-4 configuration, which was used for both freight and passenger service.^[21] Mallet locomotives went through a similar transformation and were upgraded from helpers into huge road engines with gargantuan fireboxes; their drivers increased in size in order to allow faster running.

[edit] The end of steam

The introduction of diesel-electric locomotives in the first part of the 20th century spelled the end of steam locomotives, though they were used in North America and Europe to mid-century, and continued in use in other countries to the end of the century. Steam locomotives are in general simple machines, which can be maintainable under primitive conditions and consume a wide variety of fuels. They are as a rule inefficient compared to modern diesels, requiring constant maintenance and labour to keep them operational.^[22] Water is required at many points throughout a rail network and becomes a major problem in desert areas, as are found in some regions within the United States, Australia and South Africa. In other localities the local water is unsuitable. The reciprocating mechanism on the driving wheels tend to pound the rails (see "hammer blow"), thus requiring more maintenance. Steam locomotives require several hours' boiling up before service and an end-of-day procedure to remove ash and clinker. Diesel or electric locomotives, by comparison, commence working from the first turn of the key and do not require the labour-intensive cleaning, raking and servicing after a shift.^[23] Finally, the smoke from steam locomotives is objectionable; in fact, the first electric and diesel locomotives were developed to meet smoke abatement requirements.^[23] However it should be remembered that the power for most electric trains is, in fact, derived from steam, albeit in a power station.

[edit] United States

Mainline diesel-electric locomotives first appeared on the Baltimore and Ohio Railroad, in 1935 as locomotive No. 50. The diesel reduced maintenance costs dramatically, while increasing locomotive availability. On the Chicago, Rock Island and Pacific Railroad the new units delivered over 350,000 miles (560,000 km) a year, compared with about 120,000–150,000 for a mainline steam locomotive.^[11] World War II delayed dieselisation in the U.S.A, but the pace picked up in the 1950s. Among large railroads, the Alabama, Tennessee and Northern Railroad; and the Western Pacific Railroad were among the first to completely retire steam power. By 1960, the last American Class I holdout, the Norfolk and Western Railway, discontinued steam operations. Some U.S. shortlines continued steam operations into the 1960s, and the Northwestern Steel and Wire mill in Sterling, IL, continued to operate steam locomotives until December 1980.^[24]

[edit] United Kingdom

Trials of diesel locomotives began in the United Kingdom in the 1930s but made only limited progress. One problem was that British diesel locomotives were often seriously under-powered, compared with the steam locomotives they were competing against.

After 1945, problems associated with post-war reconstruction and the availability of cheap domestic-produced coal kept steam in widespread use until the 1960s, when rising labour costs led to its withdrawal in 1968.^{[citation needed]}. At the end of steam, British Railways estimated that its steam locomotives were costing around four times more in running costs than diesels (even though most of its steam locomotives were allowed to deteriorate to a sorry state of repair before being scrapped).^{[citation needed]} The use of steam locomotives in British industry continued on an on and off basis into the late 1980s.^{[citation needed]}

[edit] South Korea

In South Korea, the first steam locomotive was the Moga 2-6-0, followed by; Sata, Pureo, Ame, Sig, Mika, Pasi, Hyeogi, Class 901, Mateo, Sori, and Tou. Used until 1967, that train is now in the Railroad Museum.

[edit] Other countries

In other countries, the conversion from steam was slower. By March 1973 in Australia, steam had vanished in all states. Diesel locomotives were more efficient and the demand for manual labour to service and repairs was less than steam. Cheap oil had cost advantages over coal.

In the USSR, the last steam locomotive (model П36, serial number 251) was built in 1956; now in the Museum of Railway Machinery at former Warsaw Rail Terminal, Saint Petersburg, Russia. In the European part of the USSR, almost all steam locomotives were replaced by diesel and electrical ones in 1960s; in Siberia with its cheap coal, steam locomotives were in active use till mid-1970s. However, some photographs exist of Russian steam locomotives at work into the 1980s, and many accurate historical records state that Russian Decapods, L-class 0-10-0s, and LV-class 2-10-0s were retired between 1980-1985, implying that the best of Russian steam ,such as the P36 class, remained on the active rosters into the 1990s. Until 1994, Russia had at least 1,000 steam locomotives stored in operable condition in case of "national emergencies" - as a result, more than 200 steam locomotives are still in working condition.^{[citation needed]}

In Finland, the first diesels were introduced in the mid-1950s and they superseded the steam locomotives during the early '60s. The State Railways (VR) operated steam locomotives until 1975.

In Poland, on non-electrified tracks steam locomotives were superseded almost entirely by diesels by the early '90s. A few steam locomotives, however, operate still from Wolsztyn. Although they are maintained operational rather as a means of preserving railway heritage and as a tourist attraction, they do haul regular scheduled trains (mostly to Poznań). Apart from that, numerous railway museums and heritage railways (mostly narrow gauge) own steam locomotives in working condition.

In South Africa an oil embargo combined with an abundance of cheap local coal, cheap labour force, ensured steam locomotives survived into the 1990s.^{[citation needed]} Locomotive engineer L. D. Porta's designs appeared on a Class 19D engine in 1979, then a former Class 25 4-8-4 engine, became a Class 26, termed the "Red Devil" No. 3450, which demonstrated an improved overall performance with decreased coal and water consumption. The single class 26 locomotive operated until the end of steam. Another class 25NC locomotive, No. 3454, nicknamed the "Blue Devil" because of its colour scheme, received modifications including a most obvious set of double side-by-side exhaust stacks. In southern Natal, two former South African Railway 2 ft (610 mm) gauge NGG16 Garratts operating on the privatised Port Shepstone & Alfred County Railway (ACR)received some L. D. Porta modifications in 1990 becoming a new NGG16A class.^[25]

China continued to build mainline steam locomotives until late in the century, even building a few examples for American tourist operations. Since China was the last main-line user of steam locomotives, ending officially at the beginning of 2006, it is plausible that many still exist in industrial operations or in more remote parts of China. Many coal mines and smaller cities, such as Pingdingshan and Hegang, maintain an active roster of JS, SY, or QJ steam locomotives bought second hand from China Rail. The last steam locomotives built in China were of the SY 2-8-2 class, built until 1999.^{[citation needed]} The last steam locomotive built in China was SY 1772, finished in 1999. As of date, at least 4 Chinese steam locomotives exist in the United States - 2 QJ's bought by RDC, a JS bought by the Boone Scenic Railway, and an SY bought by the NYSW for tourist operations, then was re-painted and modified to represent a 1920s era US locomotive.

[edit] Hopes of revival

Dramatic increases in the cost of diesel fuel prompted several initiatives to revive steam power.^[26][27] None of these has progressed to the point of production, and in the early 21st century, the steam locomotives operate only in a few isolated regions and in tourist operations.

In Germany a small number of fireless steam locomotives are still working in industrial service, e.g. at power stations.

The Swiss company Dampflokomotiv und Maschinenfabrik DLM AG delivered several new steam locomotives to rack railways in Switzerland and Austria between 1992 and 1996. One was the Brienz Rothorn Bahn.

[edit] References

1. ^ ^{a b} Payton, Philip (2004). Oxford Dictionary of National Biography. Oxford University Press. 
2. ^ Hamilton Ellis (1968). The Pictorial Encyclopedia of Railways. The Hamlyn Publishing Group, pp.24-30. 
3. ^ West Coast and R711
4. ^ Swengel p. 146.
5. ^ National Museum of American History article on locomotive crews.
6. ^ See "Compound Locomotives" by JT Van Reimsdijk Atlantic Transport Publishers 1994
7. ^ Page 152 'Steam Locomotive Design: Data and Formulæ' EA Phillipson, 1936 (Camden Miniature Steam Services have republished this recently)
8. ^ Page 154, Steam Locomotive Design:Data and Formulae, EA Phillipson, 1936
9. ^ Adams, Henry (1907): Cassell’s Engineer’s Handbook. Cassell and Co, London, page 274
10. ^ ^{a b c d e} Swengel, Frank M (1967). The American Steam Locomotive, Vol.1, The Evolution of the Steam Locomotive. Davenport, IA: MidWest Rail Publications. 
11. ^ ^{a b c d e f g} Bell, A Morton (1950): Locomotives, seventh edition. Virtue & Co Ltd, London.
12. ^ ^{a b c} Snell, John B (1971): Mechanical Engineering: Railways. Longman, London.
13. ^ Cass City Chronicle, Friday, July 29, 1938, page 3. Accessed 26 September 2007.
14. ^ U.S. National Parks Service online history resource: Pennsylvania Railroad chemical laboratory. Accessed 9 November 2006.
15. ^ Unknown author (1957): Handbook for Railway Steam Locomotive Enginemen. British Transport Commission.
16. ^ Oxford English Dictionary: Buff ¹
17. ^ Section 10, Railway Regulation Act, 1842. Her Majesty's Stationery Office.
18. ^ Van Riemsdijk, John T.: Compound locomotives, an international survey (Atlantic Transport Publishers, Penryn, England, 1994 ISBN 0 906899 61 3
19. ^ [1]
20. ^ Adams, Henry (1908). Cassell's Engineer's Handbook. London: Cassell and Company, p389. 
21. ^ Allen, Cecil J (1949): Locomotive Practice and Performance in the Twentieth Century. W Heffer and Sons Ltd, Cambridge, England.
22. ^ 1935 article on the advantages of diesel locomotives.
23. ^ ^{a b} Diesel Traction Manual for Enginemen, 15-16. British Transport Commission, 1962.
24. ^ Last locomotive to operate in the United States Library Service of Northern Illinois University, accessed 2007-11-05
25. ^ VidRail Productions, South African end of Steam: Orange Free State, Part 4, Vols. 3, 4 and 5 and Natal, Part 3, Vol. 1, in The Best of Southern African Steam, 1983-1990
26. ^ The 5AT project to develop a modern steam locomotive for British railways.
27. ^ Railway Extension Across the Andes: reactivation and modernisation of existing fleet of 75 cm gauge 2-10-2 steam locomotives.

[edit] See also

Manufacturers

• Beyer Peacock
• Neilson and Company

[edit] External links

• Database of surviving steam locomotives in North America
• Information on North American steam railroads in operation
• UK heritage railways and preserved locomotives database
• Pages for the British project to build a modern steam locomotive. The Advanced Steam Locomotive. (5AT)
• International Steam Locomotives

[edit] Books on steam locomotives

• C. E. Wolff, Modern Locomotive Practice: A Treatise on the Design, Construction, and Working of Steam Locomotives (Manchester, England, 1903)
• Henry Greenly, Model Locomotive (New York, 1905)
• G. R. Henderson, Cost of Locomotive Operation (New York, 1906)
• W. E. Dalby, Economical Working of Locomotives (London, 1906)
• A. I. Taylor, Modern British Locomotives (New York, 1907)
• E. L. Ahrons, The Development of British Locomotive Design (London, 1914)
• E. L. Ahrons, Steam Engine Construction and Maintenance (London, 1921)
• J. F. Gairns, Locomotive Compounding and Superheating (Philadelphia, 1907)
• Angus Sinclair, Development of the Locomotive Engine (New York, 1907)
• Vaughn Pendred, The Railway Locomotive, What it is and Why it is What it is (London, 1908)
• Brosius and Koch, Die Schule des Lokomotivführers (thirteenth edition, three volumes, Wiesbaden, 1909-1914)
• G. L. Fowler, Locomotive Breakdowns, Emergencies, and their Remedies (seventh edition, New York, 1911)
• Fisher and Williams, Pocket Edition of Locomotive Engineering (Chicago, 1911)
• T. A. Annis, Modern Locomotives (Adrian Michigan, 1912)
• C. E. Allen, Modern Locomotive (Cambridge, England, 1912)
• W. G. Knight, Practical Questions on Locomotive Operating (Boston, 1913)
• G. R. Henderson, Recent Development of the Locomotive (Philadelphia, 1913)
• Wright and Swift (editors) Locomotive Dictionary (third edition, Philadelphia, 1913)
• Roberts and Smith, Practical Locomotive Operating (Philadelphia, 1913)
• E. Prothero, Railways of the World (New York, 1914)
• M. M. Kirkman, The Locomotive (Chicago, 1914)
• C. L. Dickerson, The Locomotive and Things You Should Know About it (Clinton, Illinois, 1914)
• P. W. B. Semmens, A. J. Goldfinch, How Steam Locomotives Really Work (Oxford University Press, USA, 2004) ISBN 0-19-860782-2
• Gerald A Dee, A Lifetime of Railway Photography in Photographer Profile, Train Hobby Publications, Studfield, 1998. (Australian steam)
• Leon Oberg, Locomotives of Australia, Reed, Sydney, 1975.
• Swengel, F. M. The American Steam Locomotive; Vol. 1. The Evolution of the American Steam Locomotive, Midwest Rail Publication, Iowa, 1967.