Firebox (steam engine)
In a steam engine, the firebox is the area where the fuel is burned, producing heat to boil the water in the boiler. Most are somewhat box-shaped, hence the name; the hot gases generated in the firebox are pulled through a rack of tubes running through the boiler. In the standard steam locomotive firetube type boiler, the firebox is surrounded by water space on five sides; the bottom of the firebox is open to atmospheric pressure, but covered by fire grates or a firing pan. If the engine burns solid fuel, like wood or coal, there is a grate covering most of the bottom of the firebox to hold the fire. An ashpan, mounted underneath the firebox and below the grates and collects hot embers and other solid combustion waste as it falls through the grates. In a coal-burning locomotive, the grates may be shaken to clean dead ash from the bottom of the fire, they are shaken either manually or by a powered grate shaker. Wood-burning locomotives have fixed grates. Wood ash is powder which will fall through the grates with no more agitation required than the vibrations of the locomotive rolling down the track.
The fire grates must be replaced periodically due to the extreme heat. Combustion air enters through the bottom of the firebox and airflow is controlled by damper doors above the ash collection pocket of the ash pan. A locomotive that burns liquid fuel - "Bunker C" fuel oil or similar heavy oil - does not have grates. Instead, they have a heavy metal gauge firing pan bolted tight against the bottom of the firebox; the firing pan is covered with firebrick and the firebox has a firebrick lining up to the level of the firebox door, all the way around the firebox. The oil burner is a nozzle containing a slot for the oil to flow out onto a steam jet which atomizes the oil into a fine mist which ignites in the firebox; the oil burner nozzle is mounted in the front of the firebox, protected by a hood of firebrick, aimed at the firebrick wall below the firebox door. Dampers control air flow to the oil fire. There is a large brick arch attached to the front wall of the firebox beneath the firetubes; this extends backwards over the front third to half of the firebed.
It is supported on thermic syphons, or circulators. The brick arch directs heat and smoke back over the fire towards the rear of the firebox. Visible smoke contains unburned combustible carbon particles and combustible gasses; the purpose of this redirection is to cause more complete combustion of these particles and gasses which make the locomotive more efficient and causes less visible smoke to be emitted from the stack. Without the arch and visible smoke would be sucked straight into the firetubes without having been burned, causing visible smoke to be emitted at the stack; the brick arch and its supports require periodic replacement due to the extreme heat. Firetubes are attached to one wall of the firebox and carry the hot gaseous products of combustion through the boiler water, heating it, before they escape to the atmosphere. Firetubes serve the additional purpose of staying the flat tube sheets so that only the top of the front flue sheet and the bottom of the rear flue sheet must be separately braced.
The metal walls of the firebox are called sheets, which are separated and supported by stays. The stays brace the "sheets" against pressure. Ideally, they should be located at right angles to the sheets, but since the outer sheet is radial and the top of the firebox is flat by comparison, such a relationship to both sheets is impossible; the actual location of the stays is a compromise. Since stay breakage is hidden, the stays have longitudinal holes, called tell-tales, drilled in them which will blow water and steam, revealing if they are broken. A boiler with more than 5 broken stays, or two next to each other, must be taken out of service and the stays replaced; the fusible plugs located in the highest part of the crown sheet, have a soft metal alloy core which melts out if the water level in the boiler gets too low. Steam and water blowing into the firebox both alerts the locomotive crew to the low water condition and helps put out the fire. Not all locomotives are equipped with fusible plugs.
Fusible plugs should be replaced at regular intervals, about every three months for a locomotive in regular service, because the soft metal alloy core will melt out over time if the boiler water is carried at proper levels. The "mudholes," or washout plugs, allow access to the interior of the boiler for washing and scraping away boiler mud and scale; the sheets on the left and right are called "side sheets" while the sheet in the front of the firebox is the flue sheet. The "front flue sheet" is at the rear of the smokebox; the "rear sheet" has the door opening in it. The crown sheet is the top of the firebox; the crown sheet must be covered by water at all times. If the water level drops below the crown sheet, it will become overheated and start to melt and deform sagging between the crown stays. If the condition continues, the crown sheet will be forced off the crown stays by the pressure in the boiler, resulting in a boiler explosion; this condition caused by human error or inattention, is the single greatest cause of a locomotive boiler explosion.
The top of the boiler over the firebox is radial to match the contour of the boiler.
A smokebox is one of the major basic parts of a steam locomotive exhaust system. Smoke and hot gases pass from the firebox through tubes where they pass heat to the surrounding water in the boiler; the smoke enters the smokebox, is exhausted to the atmosphere through the chimney. Early locomotives had no smokebox and relied on a long chimney to provide natural draught for the fire but smokeboxes were soon included in the design for two main reasons. Firstly and most the blast of exhaust steam from the cylinders, when directed upwards through an airtight smokebox with an appropriate design of exhaust nozzle draws hot gases through the boiler tubes and flues and fresh combustion air into the firebox. Secondly, the smokebox provides a convenient collection point for ash and cinders drawn through the boiler tubes, which can be cleaned out at the end of a working day. Without a smokebox, all char must pass up the chimney or will collect in the tubes and flues themselves blocking them; the smokebox appears to be a forward extension of the boiler although it contains no water and is a separate component.
Smokeboxes are made from riveted or welded steel plate and the floor is lined with concrete to protect the steel from hot char and acid or rainwater attack. To assist the passage of the smoke and hot gases, a blower is used; this is a pipe ending in a ring containing pin-sized holes. The steam draws further gases through the tubes; this in turn causes air to be drawn through the firehole, making the fire burn hotter. When the locomotive is in motion, exhaust steam passes through the blastpipe, located within the smokebox; the steam is ejected through the chimney. The blastpipe is. Ashes and soot which may be present in the smoke are deposited in the smokebox; the front of the smokebox has a door, opened to remove these deposits at the end of each locomotive's working day. The handle must be tightened to prevent air leaks, which would reduce the draw on the fire and can allow any unburnt char at the bottom of the smokebox to catch fire there; some smokebox doors have a single handle in the form of a wheel.
On many steamrollers an extension to the body of the smokebox houses the bearing which supports the front roller. Due to limitations of space, these rollers have a drop-down flap instead of a circular smokebox door; the smokebox incorporates the main steam pipes from the regulator, one leading to each valve chest, a part of the cylinder casting. These may pass through the smokebox wall to join with the cylinder or may stay within the profile of the smokebox. Inside steam pipes do not require lagging as the smokebox keeps them warm, but outside steam pipes are more common for locomotives with cylinders outside the frames; some locomotive classes used both types depending on the date. Because heat losses from the smokebox are of little consequence, it is not lagged. In most cases it appears to be the same diameter as the boiler in the finished locomotive but this only because of the boiler cladding. Tank engines had their water tanks stop short of the unlagged smokebox as it could raise the temperature of the water sufficiently to cause problems with the injectors.
British Railways standard classes use this design, where a robust mesh grille is incorporated into the smokebox, forming a filter between the front tubeplate and the exhaust. Any large pieces of char passing through the boiler tubes tend to be broken up on impact with the mesh, creating finer particles which are swept up the chimney instead of accumulating in the bottom of the smokebox; this does not negate the need to clean out the smokebox but reduces the amount of work that has to be done. In the best case, smokebox cleaning could be avoided between boiler washouts at intervals of two weeks; the classic layout of a steam locomotive has the smokebox and chimney at the front of the locomotive, referred to as travelling "smokebox-first". Some designs reversed the layout to avoid problems caused by having the exhaust blowing back onto the crew. A spark arrester is installed within the smokebox; this may take the form of a cylindrical mesh running from the top of the blast pipe to the bottom of the chimney.
The purpose of a spark arrester is to prevent excessively large fragments of hot ash from being exhausted into the environment where they may pose a fire risk. For this reason, spark arresters are installed on locomotives running through dry environments, they should not be confused with the external spark arrestors fitted to some locomotives. The presence of a spark arrester may have a thermodynamic effect, distorting the draw of air over the fire and thereby reducing total power output, thus their use can be contentious. Locomotives fitted with a superheater will have a superheater header in the smokebox. Steam enters the header as "wet" steam, passes through a superheater element; this takes the form of a pipe. The steam enters a separate chamber in this time as superheated or dry steam; the advantage of superheating is that the steam has greater expansive properties when entering the cylinders, so more power can be gained from a smaller amoun
Baldwin Locomotive Works
The Baldwin Locomotive Works was an American manufacturer of railroad locomotives from 1825 to 1956. Located in Philadelphia, it moved to nearby Eddystone, Pennsylvania, in the early 20th century; the company was for decades the world's largest producer of steam locomotives, but struggled to compete as demand switched to diesel locomotives. Baldwin produced the last of its 70,000-plus locomotives in 1956 and went out of business in 1972; the company has no relation to the E. M. Baldwin and Sons locomotive builder of Australia; the Baldwin Locomotive Works had a humble beginning. Matthias W. Baldwin, the founder, was a jeweller and whitesmith, who, in 1825, formed a partnership with a machinist, engaged in the manufacture of bookbinders' tools and cylinders for calico printing. Baldwin designed and constructed for his own use a small stationary engine, the workmanship of, so excellent and its efficiency so great that he was solicited to build others like it for various parties, thus led to turn his attention to steam engineering.
The original engine was in use and powered many departments of the works for well over 60 years, is on display at the Smithsonian Institution in Washington, DC. In 1831, at the request of the Philadelphia Museum, Baldwin built a miniature locomotive for exhibition, such a success that he received that year an order from a railway company for a locomotive to run on a short line to the suburbs of Philadelphia; the Camden and Amboy Railroad Company had shortly before imported a locomotive from England, stored in Bordentown, New Jersey. It had not yet been assembled by Isaac Dripps, he made notes of the principal dimensions. Aided by these figures, he commenced his task; the difficulties attending the execution of this first order were such that they are not understood by present-day mechanics. Modern machine tools did not exist, it was under such circumstances that his first locomotive, christened Old Ironsides, was completed and tried on the Philadelphia and Norristown Railroad on November 23, 1832.
It was at once put in active service, did duty for over 20 years. It was a four-wheeled engine; the wheels were of heavy cast iron hubs, with wooden spokes and rims, wrought iron tires, the frame was made of wood placed outside the wheels. It had a 30 inches diameter boiler. Top speed was 28 mph. Baldwin struggled to survive the Panic of 1837. Production fell from 40 locomotives in 1837 to just nine in 1840 and the company was in debt; as part of the survival strategy, Matthias Baldwin took on two partners, George Vail and George Hufty. Although the partnerships proved short-lived, they helped Baldwin pull through the economic hard times. Zerah Colburn was one of many engineers. Between 1854 and 1861, when Colburn went to work more or less permanently in London, the journalist was in frequent touch with M. W. Baldwin, as recorded in Zerah Colburn: The Spirit of Darkness. Colburn was full of praise for the quality of Baldwin's work. In the 1850s, railroad building became a national obsession, with many new carriers starting up in the Midwest and South.
While this helped drive up demand for Baldwin products, it increased competition as more companies entered the locomotive production field. Still, Baldwin had trouble keeping pace with orders and in the early 1850s began paying workers piece-rate pay. Taking advantage of human nature, this increased incentives and productivity. By 1857, the company employed 600 men, but another economic downturn, this time the Panic of 1857, cut into business again. Output fell by 50 percent in 1858; the Civil War at first appeared disastrous for Baldwin. According to John K. Brown in The Baldwin Locomotive Works, 1831-1915: A Study in American Industrial Practice, at the start of the conflict Baldwin had a great dependence on Southern railways as its primary market. In 1860, nearly 80 percent of Baldwin's output went to carriers in states that would soon secede from the Union; as a result, Baldwin's production in 1861 fell more than 50 percent compared to the previous year. However, the loss in Southern sales was counterbalanced by purchases by the U.
S. Military Railroads and the Pennsylvania Railroad, which saw its traffic soar, as Baldwin produced more than 100 engines for carriers during the 1861–1865 war. By the time Matthias Baldwin died in 1866, his company was vying with Rogers Locomotive and Machine Works for the top spot among locomotive producers. By 1870 Baldwin had taken the lead and a decade it was producing 2½ times as many engines as its nearest competitor, according to the U. S. Manufacturing Census. In 1897 the Baldwin Locomotive Works was presented as one of the examples of successful shop management in a series of articles by Horace Lucian Arnold; the article described the Piece Rate System used in the shop management. Burton commented, that "in the Baldwin Locomotive Works... piecework rates are altered... Some rates have remained unchanged for the past twenty years, a workman is there more esteemed when
John B. Jervis
John Bloomfield Jervis was an American civil engineer. America's leading consulting engineer of the antebellum era, Jervis designed and supervised the construction of five of America's earliest railroads, was chief engineer of three major canal projects, designed the first locomotive to run in America and built the 41-mile Croton Aqueduct – New York City's fresh water supply from 1842 to 1891 – and was a consulting engineer for the Boston water system. John Bloomfield Jervis was born in 1795 at Huntington, New York, on Long Island, the son of Timothy Jervis, a carpenter, Phoebe Bloomfield, the eldest of seven children. Jervis moved with his family to Fort Stanwix in upstate New York in 1798 when his father purchased a farm and ran a lumber business. In October 1817 at the age of 22, Jervis was hired by Chief Engineer Benjamin Wright of the Erie Canal as an axeman in a survey party to locate the canal west of Rome, New York; the role of the axemen was to clear away brush and trees along a "trace" four feet wide.
In the spring of 1818, Jervis became a rodman until the canal was located from Rome to Montezuma in July 10, 1818. By the end of 1818, Jervis was promoted to resident engineer in charge of a canal section seventeen miles long and promoted to General Superintendent of the Eastern Division in 1824. Jervis left the Erie Canal in early 1825 to again work with Benjamin Wright on the Delaware and Hudson Canal Company. In 1827, Jervis became the chief engineer for the Hudson. In this position, he convinced the board of directors to test locomotives for the gravity railroad feeding coal to the canal terminal. Among the four engines imported for the experiment was the Stourbridge Lion, built by Foster and Company of England and became the first locomotive to run in the Western Hemisphere. In 1831, he became the chief engineer for the Mohawk and Hudson Railroad, a predecessor of the New York Central, two years he was appointed chief engineer of upstate New York's Chenango Canal project and helped in its design and construction.
In 1836, Jervis was chosen as the chief engineer on the 41-mile long Croton Aqueduct. After his work on the Croton Aqueduct, Jervis served as a consulting engineer for the Boston water system from 1846 to 1848. In the 1850s and into the early 1860s he worked on railroads in the midwestern United States, serving as chief engineer for both the Michigan Southern and Northern Indiana Railroad and Rock Island Railroad serving as President of the latter from 1851 to 1854, the Pittsburgh, Fort Wayne and Chicago Railway. Jervis retired in 1864 to his homestead in Rome, New York, but he continued to work in the area. In 1869, he helped form the Merchants Iron Mill, known today as the Rome Iron Mill in upstate New York industry, he was the founder of the Rome, New York public library, named for him. Much of the remainder of Jervis's life was spent writing, he published The Question of Labor and Capital on economics in 1877. Jervis' first steam locomotive design was the DeWitt Clinton while working as chief engineer for the Mohawk and Hudson Railroad in 1831.
The following year he built the first steam locomotive with a leading bogie, a four-wheel leading truck that guides the locomotive into curves. This 4-2-0 locomotive, which had two powered driving wheels on a rear axle underneath the locomotive's firebox, became known as the Jervis type; the Mohawk & Hudson Rail Road began operating the 4-2-0 in 1832. In 1836, Jervis was chosen as the chief engineer on the 41-mile Croton Aqueduct, which operated from 1842 to 1865, bringing fresh water to New York City. Many of Jervis's original diagrams for this project are now preserved at both the Smithsonian Institution and the Library of Congress in Washington, D. C; the High Bridge which still stands across the Harlem River in New York City, connecting Manhattan and the Bronx, was part of this project. Upon his death, Jervis bequeathed his homestead to the city of Rome to use as the location for a public library, his personal library now forms the John B. Jervis collection of the Jervis Public Library; the building was listed on the National Register of Historic Places in 1982.
In 1927, the Delaware and Hudson Railroad built an experimental steam locomotive, designed to run at 400 psi steam pressure. Jervis; the city of Port Jervis, New York, is named in his honor. The city was a port on the former Delaware and Hudson Canal, which he designed, is located at the adjoining borders of New York, New Jersey, Pennsylvania. Railway Property The Construction and Management of Railways Labor and Capital Notes Further reading Jervis, John B.. The Reminiscences of John B. Jervis. Syracuse University Press, New York. ISBN 0-8156-0077-1. CS1 maint: Multiple names: authors list CS1 maint: Extra text: authors list Larkin, F. Daniel. John B. Jervis: An American Engineering Pioneer. Iowa State University Press. ISBN 0-8138-0355-1. Museum of the City of New York, The Croton Aqueduct. Retrieved March 9, 2005. White, John H, Jr. America's Most Noteworthy Railroaders, Railroad History, 154, p. 9-15. John B. Jervis drawings from the Jervis Public Library on New York Heritage Digital Collections Art and the empire city: New York, 1825-1861, an exhibition catalog from The Metropolitan Museum of Art, which contains material on Jervis ASCE: John Bloomfield Jervis
4-4-0 is a locomotive type with a classification that uses the Whyte notation for the classification of steam locomotives by wheel arrangement and represents the arrangement: four leading wheels on two axles, four powered and coupled driving wheels on two axles, a lack of trailing wheels. Due to the large number of the type that were produced and used in the United States, the 4-4-0 is most known as the American type, but the type subsequently became popular in the United Kingdom, where large numbers were produced; every major railroad that operated in North America in the first half of the 19th century owned and operated locomotives of this type. The first use of the name American to describe locomotives of this wheel arrangement was made by Railroad Gazette in April 1872. Prior to that, this wheel arrangement was known as a eight-wheeler; this locomotive type was so successful on railroads in the United States of America that many earlier 4-2-0 and 2-4-0 locomotives were rebuilt as 4-4-0s by the middle of the 19th century.
Several 4-4-0 tank locomotives were built, but the vast majority of locomotives of this wheel arrangement were tender engines. Five years after new locomotive construction had begun at the West Point Foundry in the United States with the 0-4-0 Best Friend of Charleston in 1831, the first 4-4-0 locomotive was designed by Henry R. Campbell, at the time the chief engineer for the Philadelphia and Norristown Railway. Campbell received a patent for the design in February 1836 and soon set to work building the first 4-4-0. At the time, Campbell's 4-4-0 was a giant among locomotives, its cylinders had a 14 inches bore with a 16 inches piston stroke, it boasted 54 inches diameter driving wheels, could maintain 90 pounds per square inch of steam pressure and weighed 12 short tons. Campbell's locomotive was estimated to be able to pull a train of 450 short tons at 15 miles per hour on level track, outperforming the strongest of Baldwin's 4-2-0s in tractive effort by about 63%. However, the frame and driving gear of his locomotive proved to be too rigid for the railroads of the time, which caused Campbell's prototype to be derailment-prone.
The most obvious cause was the lack of a weight equalizing system for the drivers. At about the same time as Campbell was building his 4-4-0, the company of Eastwick and Harrison was building its own version of the 4-4-0; this locomotive, named Hercules, was completed in 1837 for the Beaver Meadow Railroad. It was built with a leading bogie, separate from the locomotive frame, making it much more suitable for the tight curves and quick grade changes of early railroads; the Hercules suffered from poor tracking, corrected by giving it an effective springing system when returned to its builder for remodeling. Though the Hercules and its successors from Eastwick and Harrison proved the viability of the new wheel arrangement, the company remained the sole builders of this type of locomotive for another two years. Norris Locomotive Works built that company's first 4-4-0 in 1839, followed by Rogers Locomotive and Machine Works, the Locks and Canals Machine Shop and the Newcastle Manufacturing Company in 1840.
After Henry Campbell sued other manufacturers and railroads for infringing on his patent, Baldwin settled with him in 1845 by purchasing a license to build 4-4-0s. As the 1840s progressed, the design of the 4-4-0 changed little, but the dimensions of a typical example of this type increased; the boiler was lengthened, drivers grew in diameter and the firegrate was increased in area. Early 4-4-0s were short enough that it was most practical to connect the pistons to the rear drivers, but as the boiler was lengthened, the connecting rods were more connected to the front drivers. In the 1850s, locomotive manufacturers began extending the wheelbase of the leading bogie and the drivers as well as the tender bogies. By placing the axles farther apart, manufacturers were able to mount a wider boiler above the wheels that extended beyond the sides of the wheels; this gave newer locomotives increased heating and steaming capacity, which translated to higher tractive effort. It was in this decade that 4-4-0 locomotives had assumed the appearance for which they would be most recognized by railways and people around the world.
The design and subsequent improvements of the 4-4-0 configuration proved so successful that, by 1872, 60% of Baldwin's locomotive construction was of this type and it is estimated that 85% of all locomotives in operation in the United States were 4-4-0s. However, the 4-4-0 was soon supplanted by bigger designs, like the 2-6-0 and 2-8-0 though the 4-4-0 wheel arrangement was still favored for express services; the widespread adoption of the 4-6-0 and larger locomotives helped seal its fate as a product of the past. Although superseded in North American service by the early 20th century, Baldwin Locomotive Works produced two examples for the narrow gauge Ferrocarriles Unidos de Yucatán in early 1946 the last engines of this wheel arrangement intended for general use. A number of individual engines have been custom-built for Theme Parks in recent years, resembling early designs in appearance; the first British locomotives to use this wheel arrangement were the 7 ft 1⁄4 in broad gauge 4-4-0 tank engine designs which appeared from 1849.
The first British tender locomotive class, although of limited success, was the broad gauge Waverley class of the Great Western Railway, designed by Daniel Gooch and built by Robert Stephenson & Co. in 1855. The first American-style British 4-4-0 tender locomotive on 4 ft 8 1⁄2 in standard gauge, desi
Pressure is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure is the pressure relative to the ambient pressure. Various units are used to express pressure; some of these derive from a unit of force divided by a unit of area. Pressure may be expressed in terms of standard atmospheric pressure. Manometric units such as the centimetre of water, millimetre of mercury, inch of mercury are used to express pressures in terms of the height of column of a particular fluid in a manometer. Pressure is the amount of force applied at right angles to the surface of an object per unit area; the symbol for it is p or P. The IUPAC recommendation for pressure is a lower-case p. However, upper-case P is used; the usage of P vs p depends upon the field in which one is working, on the nearby presence of other symbols for quantities such as power and momentum, on writing style. Mathematically: p = F A, where: p is the pressure, F is the magnitude of the normal force, A is the area of the surface on contact.
Pressure is a scalar quantity. It relates the vector surface element with the normal force acting on it; the pressure is the scalar proportionality constant that relates the two normal vectors: d F n = − p d A = − p n d A. The minus sign comes from the fact that the force is considered towards the surface element, while the normal vector points outward; the equation has meaning in that, for any surface S in contact with the fluid, the total force exerted by the fluid on that surface is the surface integral over S of the right-hand side of the above equation. It is incorrect to say "the pressure is directed in such or such direction"; the pressure, as a scalar, has no direction. The force given by the previous relationship to the quantity has a direction, but the pressure does not. If we change the orientation of the surface element, the direction of the normal force changes accordingly, but the pressure remains the same. Pressure is distributed to solid boundaries or across arbitrary sections of fluid normal to these boundaries or sections at every point.
It is a fundamental parameter in thermodynamics, it is conjugate to volume. The SI unit for pressure is the pascal, equal to one newton per square metre; this name for the unit was added in 1971. Other units of pressure, such as pounds per square inch and bar, are in common use; the CGS unit of pressure is 0.1 Pa.. Pressure is sometimes expressed in grams-force or kilograms-force per square centimetre and the like without properly identifying the force units, but using the names kilogram, kilogram-force, or gram-force as units of force is expressly forbidden in SI. The technical atmosphere is 1 kgf/cm2. Since a system under pressure has the potential to perform work on its surroundings, pressure is a measure of potential energy stored per unit volume, it is therefore related to energy density and may be expressed in units such as joules per cubic metre. Mathematically: p =; some meteorologists prefer the hectopascal for atmospheric air pressure, equivalent to the older unit millibar. Similar pressures are given in kilopascals in most other fields, where the hecto- prefix is used.
The inch of mercury is still used in the United States. Oceanographers measure underwater pressure in decibars because pressure in the ocean increases by one decibar per metre depth; the standard atmosphere is an established constant. It is equal to typical air pressure at Earth mean sea level and is defined as 101325 Pa; because pressure is measured by its ability to displace a column of liquid in a manometer, pressures are expressed as a depth of a particular fluid. The most common choices are water; the pressure exerted by a column of liquid of height h and density ρ is given by the hydrostatic pressure equation p = ρgh, where g is the gravitational acceleration. Fluid density and local gravity can vary from one reading to another depending on local factors, so the height of a fluid column
On a steam locomotive, a driving wheel is a powered wheel, driven by the locomotive's pistons. On a conventional, non-articulated locomotive, the driving wheels are all coupled together with side rods. On diesel and electric locomotives, the driving wheels may be directly driven by the traction motors. Coupling rods are not used, it is quite common for each axle to have its own motor. Jackshaft drive and coupling rods were used in the past but their use is now confined to shunting locomotives. On an articulated locomotive or a duplex locomotive, driving wheels are grouped into sets which are linked together within the set. Driving wheels are larger than leading or trailing wheels. Since a conventional steam locomotive is directly driven, one of the few ways to'gear' a locomotive for a particular performance goal is to size the driving wheels appropriately. Freight locomotives had driving wheels between 40 and 60 inches in diameter; some long wheelbase locomotives were equipped with blind drivers.
These were driving wheels without the usual flanges, which allowed them to negotiate tighter curves without binding. The driving wheels on express passenger locomotives have come down in diameter over the years, e.g. from 8 ft 1 in on the GNR Stirling 4-2-2 of 1870 to 6 ft 2 in on the SR Merchant Navy Class of 1941. This is. On locomotives with side rods, including most steam and jackshaft locomotives, the driving wheels have weights to balance the weight of the coupling and connecting rods; the crescent-shaped balance weight is visible in the picture on the right. In the Whyte notation, driving wheels are designated by numbers in the set; the UIC classification system counts the number of axles rather than the number of wheels and driving wheels are designated by letters rather than numbers. The suffix'o' is used to indicate independently powered axles; the number of driving wheels on locomotives varied quite a bit. Some early locomotives had as few as two driving wheels; the largest number of total driving wheels was 24 on the 2-8-8-8-4 locomotives.
The largest number of coupled driving wheels was 14 on the ill-fated AA20 4-14-4 locomotive. The term driving wheel is sometimes used to denote the drive sprocket which moves the track on tracked vehicles such as tanks and bulldozers. Many American roots artists, such as The Byrds, Tom Rush, The Black Crowes and the Canadian band Cowboy Junkies have performed a song written by David Wiffen called "Driving Wheel", with the lyrics "I feel like some old engine/ That's lost my driving wheel."These lyrics are a reference to the traditional blues song "Broke Down Engine Blues" by Blind Willie McTell, 1931. It was directly covered by Bob Dylan and Johnny Winter. Many versions of the American folk song "In the Pines" performed by artists such as Leadbelly, Mark Lanegan, Nirvana reference a decapitated man's head found in a driving wheel. In addition, it is that Chuck Berry references the locomotive driving wheel in "Johnny B. Goode" when he sings, "the engineers would see him sitting in the shade / Strumming with the rhythm that the drivers made."