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A steam locomotive is a railway locomotive that produces its pulling power through a steam engine. These locomotives are fueled by burning combustible material, usually coal, wood or oil, to produce steam in a boiler, which drives the steam engine. Both fuel and water supplies are carried with the locomotive, either on the locomotive itself or in wagons (tenders) pulled behind.
Steam locomotives were first developed in Great Britain during the early 19th century and dominated railway transport until the middle of the 20th century. From the early 1900s they were gradually superseded by electric and diesel locomotives.
The earliest railways employed horses to draw carts along railway tracks.
As the development of steam engines progressed through the 18th century, various attempts were made to apply them to road and railway use.[1] In 1784, William Murdoch, a Scottish inventor, built a prototype steam road locomotive.[2] An early working model of a steam rail locomotive was designed and constructed by steamboat pioneer John Fitch in the US probably during the 1780s or 1790s.[3] His steam locomotive used interior bladed wheels guided by rails or tracks. The model still exists at the Ohio Historical Society Museum in Columbus.[4]
The first full-scale working railway steam locomotive was built by Richard Trevithick in the United Kingdom and, on 21 February 1804, the world's first railway journey took place as Trevithick's unnamed steam locomotive hauled a train along the tramway from the Pen-y-darren ironworks, near Merthyr Tydfil to Abercynon in South Wales.[5]
[6] Accompanied with Andrew Vivian, it ran with mixed success.[1] The design incorporated a number of important innovations that included using high-pressure steam which reduced the weight of the engine and increased its efficiency. Trevithick visited the Newcastle area in 1804 and he had a ready audience of colliery owners and engineers. The visit was so successful that the colliery railways in north-east England became the leading centre for experimentation and development of the steam locomotive.[7] Trevithick continued his own steam propulsion experiments through another trio of locomotives, concluding with the Catch Me Who Can in 1808. Four years later, the successful twin-cylinder locomotive Salamanca by Matthew Murray for the edge railed rack and pinion Middleton Railway debuted in 1812.[8] In 1825 George Stephenson built the Locomotion for the Stockton and Darlington Railway, north-east England, which was the first public steam railway in the world. In 1829, he built The Rocket which was entered in and won the Rainhill Trials. This success led to Stephenson establishing his company as the pre-eminent builder of steam locomotives used on railways in the UK, US and much of Europe.[9] The Liverpool and Manchester Railway opened a year later making exclusive use of steam power for passenger and goods trains.
The US 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. Many of the earliest locomotives for American railroads were imported from Great Britain, including the Stourbridge Lion and the John Bull (still the oldest operable engine-powered vehicle in the United States of any kind, as of 1981) but a domestic locomotive manufacturing industry was quickly established, with locomotives like the DeWitt Clinton being built in the 1830s.[9]
The first railway service in Continental Europe (or for that matter, anywhere outside the UK and the US) was opened on 5 May 1835 in Belgium, between Mechelen and Brussels. The name of the locomotive used was The Elephant.
In Germany the first working steam locomotive was a rack-and-pinion engine, similar to the Salamanca, designed by the British locomotive pioneer John Blenkinsop. Built in June 1816 by Johann Friedrich Krigar in the Royal Berlin Iron Foundry (Königlichen Eisengießerei zu Berlin), the locomotive ran on a circular track in the factory yard. It was the first locomotive to be built on the European mainland and the first steam-powered passenger service, because curious onlookers could ride in the attached coaches for a fee. It is portrayed on a New Year's badge for the Royal Foundry dated 1816. Another locomotive was built using the same system in 1817. They were to be used on pit railways in Königshütte and in Luisenthal on the Saar (today part of Völklingen), but neither could be returned to working order after being dismantled, moved and reassembled. On 7 December 1835 the Adler ran for the first time between Nuremberg and Fürth on the Bavarian Ludwig Railway. It was the 118th engine from the locomotive works of Robert Stephenson and stood under patent protection.
In 1837 the first steam railway started in Austria on the Emperor Ferdinand Northern Railway between Vienna-Floridsdorf and Deutsch-Wagram. The oldest continually working steam engine in the world also runs in Austria: the GKB 671 built in 1860, has never been taken out of service, and is still used for special excursions.
In 1838 the third steam locomotive to be built in Germany, the Saxonia, was manufactured by the Maschinenbaufirma Übigau near Dresden, built by Prof. Johann Andreas Schubert. The first independently designed locomotive in Germany was the Beuth built by August Borsig in 1841. In 1848 the first locomotive produced by Henschel-Werke in Kassel, the Drache, was delivered.
The first railway line over Swiss territory was the Strasbourg–Basle line opened in 1844. Three years later, in 1847, the first fully Swiss railway line, the Spanisch Brötli Bahn, from Zürich to Baden was opened.
03. Water (inside the boiler)
04. Smokebox 05. Cab
06. Tender 07. Steam Dome
08. Safety Valve
09. Regulator Valve
10. Superheater Header in smokebox
11. Piston 12. Blastpipe
13. Valve Gear 14. Regulator Rod
15. Drive Frame 16. Rear Pony Truck
17. Front Pony Truck
18. Bearing and Axlebox
19. Leaf Spring 20. Brake shoe
21. Air brake pump
22. (Front) Centre Coupler,
23. Whistle 24. Sandbox.
Although other types of boiler have been tried both historically and laterally with steam locomotives, their use did not become widespread, and the firebox fire-tube boiler has been the dominant source of power in the age of steam locomotion from the Rocket in 1829 to the Mallard in 1938 and beyond.
The steam locomotive, when fired up, typically employs a steel firebox fire-tube boiler that contains a heat source to the rear, which generates and maintains a head of steam within the pressurised partially water filled area of the boiler to the front.
The heat source, contained within the firebox, is the energy released by the combustion, typically of a solid or liquid fuel, with the by-product of hot combustion gases. If wood, coal or coke is used as the combustion material it is introduced through a door, typically by a fireman, onto a set of grates where ashes fall away from the burning fuel. If oil is used a door provides for adjusting the air flow, maintenance or for cleaning the oil jets.
The fire-tube boiler is characterised by internal tubes connected to the firebox that guide the smoke and hot combustion gases through the pressurised wet area of the boiler. These tubes greatly increase the contact area between the hot and the wet areas of the boiler and this increases the efficiency of the thermal conduction and thermal radiation processes of heat transfer between the two. The combustion gases emerge from the ends of the fire-tubes at the front of the boiler and are discharged via the smokebox to the chimney (or stack US). Surrounding the boiler layers of insulation or lagging minimise heat loss to the surroundings.
The amount of pressure in the boiler can be monitored by a gauge mounted in the cab and excessive steam pressure can be released manually by the driver or fireman. Alternatively in conditions of high boiler pressure, a safety valve may be triggered to reduce pressure and prevent the boiler violently bursting, which had previously resulted in injuries and fatalities to nearby individuals, as well as extensive damage to the locomotive and nearby structures.
At the front of the boiler is the smokebox, where used exhaust steam is injected, with the effect of increasing the volume (or draw) of smoke and combustion gases pulled through the fire tubes in the boiler and out through the chimney. Thermal efficiency considerations of a typical fire-tube boiler led engineers such as Nigel Gresley to consider innovations such as the water-tube boiler which he trialled on the LNER Class W1; however, these designs required a lengthy teething process, and there was insufficient will at the time.
The steam generated in the boiler is used to drive the locomotive and also for other purposes (whistles, brakes, pumps, passenger car heating, etc.). The constant use of steam requires the boiler to have water continually pumped into it (usually by automatic means). The source of this water is an unpressurised tank that is usually part of the locomotive's tender or is wrapped around the boiler in the case of a tank locomotive. Periodic stops are required to refill the water.
During operation, the boiler's water level is constantly monitored, normally via a transparent tube referred to as a sight glass, or with a gauge. Maintaining a proper water level is central to the efficient and safe operation of the boiler. If the water level is too high, steam production is decreased, efficiency is lost and in extreme cases, water will be carried out with the steam into the cylinders, possibly causing mechanical damage. More seriously, if the water level gets too low, the crown (top) and/or side sheets of the firebox may become exposed. Without sufficient water to absorb the heat of combustion, the firebox sheets may soften and melt, with the possible result of high-pressure steam being ejected with tremendous force through the firebox and into the locomotive's cab. The development of the fusible plug to release pressure in conditions of excessively high temperature and low water levels was designed to protect against this occurrence.
Scale may build up in boiler and prevent proper heat transfer, and corrosion will eventually degrade the boiler's materials to the point where it needs to be rebuilt or replaced. Start-up on a large engine may take hours of preliminary heating of the boiler water before sufficient steam is available.
Although the boiler is typically placed horizontally, for locomotives designed to work in locations with steep slopes it may be more appropriate to consider a vertical boiler or one mounted such that the boiler remains horizontal but the wheels are inclined to suit the slope of the rails.
The steam generated in the boiler fills the steam space above the water in the partially filled boiler. Its maximum 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 amount of steam leaving the boiler. The steam then either travels directly along and down a steam pipe to the engine unit or may first pass into the wet header of a superheater, the role of the latter being to improve thermal efficiency and eliminate water droplets suspended in the "saturated steam", the state in which it leaves the boiler. On leaving the superheater, the steam exits the dry header of the superheater and passing down a steam pipe entering 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. During a full rotation of the driving wheel, steam provides four power strokes; each cylinder receives two injections of steam per revolution. 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. Each piston is connected to the driving axle on each side by a connecting rod, the driving wheels are connected together by coupling rods to transmit power from the main driver to the other wheels. Note that at the two "dead centres", when the connecting rod is on the same axis as the crankpin on the driving wheel, the connecting rod applies no torque to the wheel. Therefore, if both cranksets could be at "dead centre" at the same time, and the wheels should happen to stop in this position, the locomotive could not be started moving. Therefore the crankpins are attached to the wheels at a 90° angle to each other, so only one side can be at dead centre at a time.
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, actuated from the driving axle or from the crankpin; the valve gear includes devices that allow reversing the engine, adjusting valve travel and the timing of the admission and exhaust events. The cut-off point determines the moment when the valve blocks 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), that controls the cut-off therefore performs a similar function to a gearshift in an automobile - maximum cut-off, providing maximum tractive effort at the expense of efficiency, is used to pull away from a standing start, whilst a cut-off as low as 10% is used when cruising, providing reduced tractive effort with lower fuel/water consumption.[10]
Exhaust steam is directed upwards to the atmosphere through the chimney, by way of a nozzle called a blastpipe that gives rise to the familiar "chuffing" sound of the steam locomotive. The blastpipe is placed at a strategic point inside the smokebox that is at the same time traversed by the combustion gases drawn through the boiler and grate by the action of the steam blast. The combining of the two streams, steam and exhaust gases, is crucial to the efficiency of any steam locomotive, and the internal profiles of the chimney (or, more strictly speaking, the ejector) require careful design and adjustment. This has been the object of intensive studies by a number of engineers (and almost totally ignored by others with sometimes catastrophic effect). The fact that the draught depends on the exhaust pressure means that power delivery and power generation are automatically self-adjusting. Among other things, a balance has to be struck between obtaining sufficient draught for combustion whilst giving the exhaust gases and particles sufficient time to be consumed. In the past, fierce draught could lift the fire off the grate, or cause the ejection of unburnt particles of fuel, dirt and pollution for which steam locomotives had an unenviable reputation. Moreover, the pumping action of the exhaust has the counter effect of exerting back pressure on the side of the piston receiving steam, thus slightly reducing cylinder power. Designing the exhaust ejector has become a specific science in which Chapelon, Giesl[11] and Porta were successive masters, and it was largely responsible for spectacular improvements in thermal efficiency and a significant reduction in maintenance time[12] and pollution.[13] A similar system was used by some early gasoline/kerosene tractor manufacturers (Advance-Rumely/Hart-Parr) – the exhaust gas volume vented through a cooling tower meant that the steam exhaust helped draw more air past the radiator.
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, is 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 a pair of driving wheels 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 four-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.
Railroads typically wanted a locomotive with fewer axles as this would reduce the cost of maintenance. The number of axles required was dictated by the maximum axle loading of the railroad in question. A builder would typically add axles until the maximum weight on any one axle was acceptable to the railroad's maximum axle loading. A locomotive with a wheel arrangement of two lead axles, two drive axles, & one trailing axle was in actuality a high speed machine. Two lead axles were necessary to have good tracking at high speeds. Two drive axles had a lower reciprocating mass than three, four, five or six coupled axles. They were thus able to turn very high speeds due to the lower reciprocating mass. A trailing axle was able to support a huge firebox, hence most locomotives with the wheel arrangement of 4-4-2 (American Type Atlantic) were called free steamers and were able to maintain steam pressure regardless of throttle setting.
The chassis or locomotive frame is the principal structure onto which the boiler is mounted and which incorporates the various elements of the running gear. The boiler is rigidly mounted on a "saddle" beneath the smokebox and front of the boiler barrel, but the firebox at the rear is allowed to slide forward and back, to allow for expansion when hot.
European locomotives usually use "plate frames", where two vertical flat plates form the main chassis, with a variety of spacers and a buffer beam at each end to keep them apart. When inside cylinders are mounted between the frames, these are a single large casting that forms a major support to the frames. The axleboxes slide up and down to give some sprung suspension, against thickened webs attached to the frame, called "hornblocks".[citation needed]
American practice for many years was to use built-up bar frames, with the smokebox saddle/cylinder structure and drag beam integrated therein. In the 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 into a single complex, sturdy but heavy casting. André Chapelon developed a similar structure but of welded construction with around 30% saving in weight for the stillborn 2-10-4 locomotives, the construction of which was begun then abandoned in 1946.[citation needed]
Generally, the largest locomotives are permanently coupled to a tender that carries the water and fuel. Often, locomotives working shorter distances do not have a tender and carry the fuel in a bunker, the water is carried in tanks placed next to the boiler either in 2 tanks alongside (pannier tank), one on top (saddle tank) or one underneath (well tank); these are called tank engines and usually have a 'T' suffix added to the Whyte notation, e.g., 0-6-0T.
The fuel used depended on what was economically available to the railway. In the UK and other parts of Europe, plentiful supplies of coal made this the obvious choice from the earliest days of the steam engine. Until 1870,[14] the majority of locomotives in the USA burnt wood but, as the Eastern forests were cleared, coal gradually became more important. Thereafter, coal became and remained the dominant fuel worldwide until the end of general use of steam locomotives. 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 it a popular steam locomotive fuel after 1900 for the southwestern railroads, particularly the Southern Pacific. In Victoria, Australia after World War II, many steam locomotives were converted to heavy oil firing. German, Russian, Australian and British railways experimented using coal dust to fire locomotives.
A number of tourist lines and heritage locomotives in Switzerland, Argentina and Australia have been using light diesel-type oil.[15]
Water was supplied at stopping places and locomotive depots from a dedicated water tower connected to water cranes or gantries. In the UK, the USA and France, 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
Swengel went on to note that "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-skinned 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.[16]
In the 1970s, L.D. Porta developed a sophisticated heavy duty chemical water treatment (Porta 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.[17][18]
A steam locomotive is normally controlled from the boiler's backhead and the crew is usually protected from the elements by a cab. A crew of at least two people is normally required to operate a steam locomotive. One, the train driver, is responsible for controlling the locomotive's starting, stopping and speed, and the fireman is responsible maintaining the fire, regulating steam pressure, and monitoring boiler and tender water levels. Due to the historical loss of operational infrastructure and staffing, preserved steam locomotives operating on the mainline will often have a support crew travelling with the train.
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 concerns. The most typical appliances are as follows:
Water (feedwater) must be delivered to the boiler to replace that which is exhausted as steam after delivering a working stroke to the pistons. As the boiler is under pressure during operation, feedwater must be forced into the boiler at a pressure that is greater than the steam pressure, necessitating the use some sort of pump. Early engines used pumps driven by the motion of the pistons (axle pumps). 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 and are carefully monitored at all times while the boiler is being fired.
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, or shaped blocks of insulating compound such as magnesia blocks[19] were attached. In the latter days of steam, "mattresses" of stitched asbestos cloth were fixed stuffed with asbestos fibre (but on separators so as not quite to touch the boiler); however in most countries, asbestos is nowadays banned for health reasons. The most common modern day material is glass wool, or wrappings of aluminium foil.
The lagging is protected by a close-fitted sheet-metal casing[20] known as boiler clothing or cleading.
Effective lagging is particularly important for fireless locomotives; however in recent times under the influence of L.D. Porta, "exaggerated" insulation has been practised for all types of locomotive on all surfaces liable to dissipate heat, such as cylinder ends and facings between the cylinders and the mainframes. This considerably reduces engine warmup time with marked increase in overall efficiency.
Early locomotives were fitted with a valve controlled by a weight suspended from the end of a lever, the steam outlet being stopped by a cone-shaped valve. As there was nothing to prevent the weighted lever from bouncing when the locomotive ran over irregularities in the track, thus wasting steam, the weight was replaced by a more stable spring-loaded column, often supplied by Salter, a well-known spring scale manufacturer. The danger of all these devices was that the driving crew could be tempted to add weight to the arm to increase pressure. Most boilers were from early times fitted with a tamper-proof "lockup" direct-loaded ball valve protected by a cowl. In the late 1850s, John Ramsbottom introduced a safety valve that became popular in Britain during the latter part of the 19th century. Not only was this valve tamper-proof, but tampering by the driver could only have the effect of easing pressure. George Richardson's safety valve was an American invention introduced in 1875[21] and was so designed as to release the steam only at the moment when the pressure attained the maximum permitted. This type of valve is in almost universal use at present. Britain's Great Western Railway was a notable exception to this rule retaining the direct loaded type until the end of its separate existence because it was considered that such a valve lost less pressure between opening and closing.
The earliest locomotives did not show the pressure of steam in the boiler, but it was possible to estimate this by the position of the safety valve arm which often extended onto the firebox back plate; gradations marked on the spring column gave a rough indication of the actual pressure. 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 introduced in 1849 and quickly gained acceptance. This is the device used today.[22] 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.
Wood-burners emit large quantities of flying sparks which necessitate an efficient spark arresting device generally housed in the smokestack. Many types were fitted,[23] the most common early type being the Bonnet stack that incorporated a cone-shaped deflector placed before the mouth of the chimney pipe plus a wire screen covering the wide stack exit; more efficient was the Radley and Hunter centrifugal type patented in 1850, (generally known as the diamond stack) incorporating baffles so orientated as to induce a swirl effect in the chamber that encouraged the embers to burn out and fall to the bottom as ash. In the self-cleaning smokebox the opposite effect was achieved: by allowing the flue gasses to strike a series of deflector plates, angled in such a way that the blast was not impaired, the larger particles were broken into small pieces that would be ejected with the blast, rather than settle in the bottom of the smokebox to be removed by hand at the end of the run. As with the arrestor, a screen was incorporated to retain any large embers.[24]
Locomotives of the British Railways standard classes fitted with self-cleaning smokeboxes were identified by a small cast oval plate marked "S.C.", fitted at the bottom of the smokebox door. These engines required different disposal procedures and the 'S.C.' plate highlighted this need to depot staff.
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.[20] In the United States, various steam-powered mechanical stokers became standard equipment and were adopted and used elsewhere including Australia and South Africa.
Introducing cold water into a boiler reduces power, and from the 1920s a variety of heaters were incorporated. The most common type for locomotives was the exhaust steam feedwater heater that piped some of the exhaust through small tanks mounted on top of the boiler or smokebox or else into the tender tank; the warm water then had to be delivered to the boiler by a small auxiliary steam pump. The rare economiser type differed in that it extracted residual heat from the exhaust gases. An example of this is the pre-heater drum(s) 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 to a small degree, 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. This is further helped by the top feed where water is introduced to the highest part of the boiler and made to trickle over a series of trays. G.J. Churchward fitted this arrangement to the high end of his domeless coned boilers other British lines such as the LBSCR fitted a few locomotives with the top feed inside a separate dome forward of the main one.
Steam locomotives consume vast quantities of water because they operate on an open cycle, expelling their steam immediately after a single use rather than recycling it in a closed loop as stationary and marine steam engines do. Water was a constant logistical problem, and for use 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 25, the "puffers which never puff"[25]) 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 U.S., 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).[26] 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 to prevent steam from escaping into the railway tunnels. These were still being used between King's Cross and Moorgate into the early 1960s.
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 compressors, which are mounted on the side of the boiler or on the smokebox front. Almost all of these compressors were of the Westinghouse single-stage or cross-compound variety. Such systems operated in the United States, Canada, Australia and New Zealand.
An alternative to the air brake is the vacuum brake, in which a steam-operated ejector is mounted on the engine instead of the air pump, to create vacuum and release the brakes. A secondary ejector or crosshead vacuum pump is used to maintain the vacuum in the system against the small leaks in the pipe connections between carriages and wagons. Vacuum systems existed on British, Indian, Western Australian and South African railway 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 or icy 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.
The pistons and valves on the earliest locomotives were lubricated by the enginemen dropping a lump of tallow down the blast pipe.[27]
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.[28] 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.[29]
When the locomotive is running under power, a draught on the fire is created by the exhaust steam directed up the chimney by the blastpipe. Without draught, the fire will quickly die down and steam pressure will fall. When the locomotive is stopped, or coasting with the regulator closed, there is no exhaust steam to create a draught, so the draught is maintained by means of the blower. This is a ring placed either around the base of the chimney, or around the blast pipe orifice, containing several small steam nozzles directed up the chimney. These nozzles are fed with steam directly from the boiler, controlled by the blower valve. When the regulator is open, the blower valve is closed; when the driver intends to close the regulator, he will first open the blower valve. It is important that the blower be opened before the regulator is closed, since without draught on the fire, there may be backdraught – air from the atmosphere blows down the chimney, causing the flow of hot gases through the boiler tubes to be reversed, with the fire itself being blown through the firehole onto the footplate, with serious consequences for the crew. The risk of backdraught is higher when the locomotive enters a tunnel because of the pressure shock. The blower is also used to create draught when steam is being raised at the start of the locomotive's duty; at any time when the driver needs to increase the draught on the fire; and to clear smoke from the driver's line of vision.[30]
In British and European practice, the locomotive usually had buffers at each end to absorb compressive loads ("buffets"[31]). 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.[32] In Britain and Europe, American style 'buckeye' and other couplers that also handle forces between items of rolling stock have become increasingly popular.
A pilot was usually fixed to the front end of locomotives, although in European and a few other railway systems, such as New South Wales, they were considered unnecessary. Plough-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 until the end of steam. Switching engines usually replaced the pilot with small steps, known as footboards. Many systems used the pilot and other design features to produce a distinctive appearance.
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 arc lamps became available in the late 1880s, they quickly replaced the older types.
Britain did not adopt bright headlights as they would affect night-adapted vision and so could mask the low-intensity oil lamps used in the semaphore signals and at each end of trains, increasing the danger of missing signals especially on busy tracks. In any case, trains' stopping distances were normally much greater than the range of headlights, and the railways were well-signalled and fully fenced to prevent livestock and people from straying onto them. Thus low-intensity oil lamps continued to be used, positioned on the front of locomotives to indicate the class of each train. Four 'lamp irons' were provided (brackets on which to place the lamps): 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 an extra lamp iron 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 all cases, equivalent lamp irons were also provided on the rear of the locomotive or tender for when the locomotive was running tender- or bunker-first.)
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.
Locomotives used bells and steam whistles from earliest days. In the United States, India and Canada, bells warned of a train in motion. In Britain, where all lines are by law fenced throughout,[33] 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. Automatic bell ringers came into widespread use in the U.S. after 1910.[34]
From early in the 20th century operating companies in such countries as Germany and Britain began to fit locomotives with in-cab signalling (AWS) which automatically applied the brakes when a signal was passed at "caution". In Britain these became mandatory in 1956. In the United States, the Pennsylvania Railroad also fitted their locomotives with such devices.
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 (1,067 mm) gauge engines in the world to have such equipment.
Numerous variations to the simple locomotive occurred as railways attempted to improve efficiency and performance.
Early steam locomotives had two cylinders, one either side, and this practice persisted as the simplest arrangement. The cylinders could be mounted between the main frames (known as 'inside' cylinders), or mounted outside the frames and driving wheels ('outside' cylinders). Inside cylinders are driven by cranks built into the driving axle; outside cylinders are driven by cranks on extensions to the driving axles.
Later designs employed three or four cylinders, mounted both inside and outside the frames, for a more even power cycle and greater power output.[35] This was at the expense of more complicated valve gear and increased maintenance requirements. In some cases the third cylinder was added 'inside' simply to allow for smaller diameter outside cylinders, and hence reduce the width of the locomotive for use on lines with a restricted loading gauge, for example the SR K1 and U1 classes.
Most British express passenger locomotives built from about 1930 to 1950 were 4-6-0 or 4-6-2 types with three or four cylinders (e.g., GWR 6000 Class, LMS Coronation Class, SR Merchant Navy Class, LNER Gresley Class A3). From 1951, all but one of the 999 new British Rail standard class steam locomotives of all types from express passenger and heavy freight to smaller mixed traffic tank locomotives used 2-cylinder configurations for easier maintenance.
Numerous technological advances improved the steam engine. Early locomotives used simple valve gear that gave full power in either forward or reverse.[22] Soon Stephenson valve gear allowed the driver to control cut-off; this was largely superseded by Walschaerts valve gear and similar patterns. Early locomotive designs using slide valves and outside admission were relatively easy to construct, but inefficient and prone to wear.[22] 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.
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