2-8-0
Under the Whyte notation for the classification of steam locomotives, 2-8-0 represents the wheel arrangement of two leading wheels on one axle in a leading truck, eight powered and coupled driving wheels on four axles and no trailing wheels. In the United States and elsewhere, this wheel arrangement is known as a Consolidation, after the Lehigh and Mahanoy Railroad’s Consolidation, the name of the first 2-8-0. Of all the locomotive types that were created and experimented with in the 19th century, the 2-8-0 was a relative latecomer; the first locomotive of this wheel arrangement was built by the Pennsylvania Railroad. Like the first 2-6-0s, this first 2-8-0 had a leading axle, rigidly attached to the locomotive's frame, rather than on a separate truck or bogie. To create this 2-8-0, PRR master mechanic John P. Laird modified an existing 0-8-0, the Bedford, between 1864 and 1865; the 2-6-0 Mogul type, first created in the early 1860s, is considered as the logical forerunner to the 2-8-0. However, a claim is made that the first true 2-8-0 engine evolved from the 0-8-0 and was ordered by the United States' Lehigh and Mahanoy Railroad, which named all its engines.
The name given to the new locomotive was Consolidation, the name, almost globally adopted for the type. According to this viewpoint, the first 2-8-0 order by Lehigh dates to 1866 and antedates the adoption of the type by other railways and coal and mountain freight haulers. From its introduction in 1866 and well into the early 20th century, the 2-8-0 design was considered to be the ultimate heavy-freight locomotive; the 2-8-0's forte was starting and moving "impressive loads at unimpressive speeds" and its versatility gave the type its longevity. The practical limit of the design was reached in 1915, when it was realised that no further development was possible with a locomotive of this wheel arrangement; as in the United States, the 2-8-0 was a popular type in Europe, again as a freight hauler. The type was used in Australia, New Zealand, Southern Africa; the 2-8-0 locomotive was used extensively throughout Australia. It served on the 5 ft 3 in broad gauge, 4 ft 8 1⁄2 in standard gauge and 3 ft 6 in narrow gauge and was employed as a freight locomotive, although it was also employed in passenger service in Victoria.
The first Australian locomotive class with this wheel arrangement consisted of 20 standard-gauge New South Wales Government Railways J Class engines, which arrived from Baldwin Locomotive Works in 1891. The Js remained in service in New South Wales until 1915. Wartime shortages between 1916 and 1920 had six engines re-entering service after being shopped and fitted with superheaters; the last engine of this class was withdrawn in 1934 and all were scrapped by 1937. The second batch of 2-8-0 locomotives to appear in Australia, between 1896 and 1916, was the NSWGR T class engines; the class was delivered from one local and several overseas builders, 151 locomotives from Beyer and Company, 84 from North British Locomotive Company, 10 from Neilson and Company, 30 from Clyde Engineering in Australia, five from Dübs and Company. During World War II, 14 of these locomotives were equipped with superheaters, which raised their tractive effort from 28,777 lbf to 33,557 lbf. From 1899, the Victorian Railways used a range of broad-gauge 2-8-0 locomotives.
The first of these locomotives were the Baldwin-built Victorian Railways V class. These engines were built at Phoenix Foundry in Victoria. By 1930, they had disappeared from the VR; the VR's next type was the 26 C class engines, which saw passenger service. In 1922, a smaller and lighter 2-8-0, the K class, was introduced for branchline freight and also passenger services; the VR introduced sixty light 2-8-0 J class engines in 1954. These worked both freight and passenger services; the first 2-8-0 engines in private service on the Midland Railway of Western Australia arrived in 1912. These were 3 ft 6 in gauge locomotives; the five in the class operated until 1958. All were gone by 1963. In 1912, some of the NSWGR T class types were purchased by the private East Greta Railway to become the South Maitland Railway, but these were converted to 2-8-2 tank locomotives; the class proved to be successful throughout its long service life, until being retired from government revenue service in 1973. During 1916, several of these same T class engines were purchased from NBL by the Commonwealth Railways for the Trans-Australian Railway.
In 1924, a private coal company, J&A Brown in NSW, obtained three ex-British military Railway Operating Division ROD 2-8-0 locomotives. Brown ordered another 10 of these locomotives, but only nine of that order arrived in Australia; the last was withdrawn in 1973. To compensate for wartime losses, Belgian railways acquired 300 2-8-0 locomotives in 1946, they were built in North America, 160 by Montreal Locomotive Works in Canada, 60 by the Canadian Locomotive Company, 80 by the American Locomotive Company in the United States. These machines proved to be reliable and were used for mixed traffic until the end of the steam era, when number 29.013 hauled the last scheduled steam passenger train from Ath to Denderleeuw on 20 December 1966. This locomotive is used on special excursions. On 16 December 2006, number 29.013 re-enacted the last 1966 run on the same route. The Canadian Pacific Railway N-2-a, b, c class locomotives were a class of altogether 182 Consolidation type locomotives, built by Montreal Locomotive Works between 1912 and 1914.
They were numbered in the range from 3600 to 3799 and were used everywhere around the sy
Valve gear
The valve gear of a steam engine is the mechanism that operates the inlet and exhaust valves to admit steam into the cylinder and allow exhaust steam to escape at the correct points in the cycle. It can serve as a reversing gear, it is sometimes referred to as the "motion". In the simple case, this can be a simple task as in the internal combustion engine in which the valves always open and close at the same points; this is not the ideal arrangement for a steam engine, because greatest power is achieved by keeping the inlet valve open throughout the power stroke while peak efficiency is achieved by only having the inlet valve open for a short time and letting the steam expand in the cylinder. The point at which steam stops being admitted to the cylinder is known as the cutoff, the optimal position for this varies depending on the work being done and the tradeoff desired between power and efficiency. Steam engines are fitted with regulators to vary the restriction on steam flow, but controlling the power via the cutoff setting is preferable since it makes for more efficient use of boiler steam.
A further benefit may be obtained by admitting the steam to the cylinder before front or back dead centre. This advanced admission assists in cushioning the inertia of the motion at high speed. In the internal combustion engine, this task is performed by cams on a camshaft driving poppet valves, but this arrangement is not used with steam engines because achieving variable engine timing using cams is complicated. Instead, a system of eccentrics and levers is used to control a D slide valve or piston valve from the motion. Two simple harmonic motions with different fixed phase angles are added in varying proportions to provide an output motion, variable in phase and amplitude. A variety of such mechanisms have been devised with varying success. Both slide and piston valves have the limitation that intake and exhaust events are fixed in relation to each other and cannot be independently optimised. Lap is provided on steam edges of the valve, so that although the valve stroke reduces as cutoff is advanced, the valve is always opened to exhaust.
However, as cutoff is shortened, the exhaust events advance. The exhaust release point occurs earlier in the power stroke and compression earlier in the exhaust stroke. Early release wastes some energy in the steam, early closure wastes energy in compressing an otherwise unnecessarily large quantity of steam. Another effect of early cutoff is that the valve is moving quite at the cutoff point, this causes'wire drawing' of the steam, another wasteful thermodynamic effect visible on an indicator diagram; these inefficiencies drove the widespread experimentation in poppet valve gears for locomotives. Intake and exhaust poppet valves could be moved and controlled independently of each other, allowing for better control of the cycle. In the end, not a great number of locomotives were fitted with poppet valves, but they were common in steam cars and lorries, for example all Sentinel lorries and railcars used poppet valves. A late British design, the SR Leader class, used sleeve valves adapted from internal combustion engines, but this class was not a success.
In stationary steam engines, traction engines and marine engine practice, the shortcomings of valves and valve gears were among the factors that lead to compound expansion. In stationary engines trip valves were extensively used. Valve gear was a fertile field of invention, with several hundred variations devised over the years. However, only a small number of these saw any widespread use, they can be divided into those that drove the standard reciprocating valves, those used with poppet valves, stationary engine trip gears used with semi-rotary Corliss valves or drop valves. Slip-eccentric - This gear is now confined to model steam engines, low power hobby applications such as steam launch engines, ranging to a few horsepower; the eccentric is loose on the crankshaft but there are stops to limit its rotation relative to the crankshaft. Setting the eccentric to the forward running and reverse running positions can be accomplished manually by rotating the eccentric on a stopped engine, or for many engines by turning the engine in the desired rotation direction, where the eccentric positions itself automatically.
The engine is pushed forwards to put the eccentric in the forward gear position and backwards to put it in the backward gear position. There is no variable control of cutoff. On the London and North Western Railway, some of the three-cylinder compounds designed by Francis William Webb from 1889 used a slip eccentric to operate the valve of the single low-pressure cylinder; these included Greater Britain and John Hick classes. Gab or hook gear - used on earliest locomotives. Allowed reversing but no control of cutoff. One component of the motion comes from a eccentric; the other component comes from a separate source the crosshead. Walschaerts or Heusinger valve gear - most common valve gear on locomotives externally mounted. Deeley valve gear - fitted to several express locomotives on the Midland Railway; the combination levers were driven, as normal, from the crossheads. Each expansion link was driven from the crosshead on the opposite side of the engine. Young valve gear - used the piston rod motion on one side of the locomotive to drive the valve gear on the other side.
Similar to the Deeley gear, but with deta
Stephenson valve gear
The Stephenson valve gear or Stephenson link or shifting link is a simple design of valve gear, used throughout the world for all kinds of steam engines. It was invented by his employees. During the 1830s the most popular valve drive for locomotives was known as gab motion in the U. K. and V-hook motion in the U. S. A; the gab motion incorporated two sets of rods for each cylinder. It was a clumsy mechanism, difficult to operate, only gave fixed valve events. In 1841 two employees in Stephenson’s locomotive works, draughtsman William Howe and pattern-maker William Williams, suggested the simple expedient of replacing the gabs with a vertical slotted link, pivoted at both ends to the tips of the eccentric rods. To change direction, the link and rod ends were bodily raised or lowered by means of a counterbalanced bell crank worked by a reach rod that connected it to the reversing lever; this not only simplified reversing but it was realised that the gear could be raised or lowered in small increments, thus the combined motion from the “forward” and “back” eccentrics in differing proportions would impart shorter travel to the valve, cutting off admission steam earlier in the stroke and using a smaller amount steam expansively in the cylinder, using its own energy rather than continuing to draw from the boiler.
It became the practice to start the engine or climb gradients at long cutoff about 70-80% maximum of the power stroke and to shorten the cutoff as momentum was gained to benefit from the economy of expansive working and the effect of increased lead and higher compression at the end of each stroke. This process was popularly known as "linking up" or “notching up”, the latter because the reversing lever could be held in precise positions by means of a catch on the lever engaging notches in a quadrant. A further intrinsic advantage of the Stephenson gear not found in most other types was variable lead. Depending on how the gear was laid out, it was possible to reduce compression and back pressure at the end of each piston stroke when working at low speed in full gear. American locomotives universally employed inside Stephenson valve gear placed between the frames until around 1900 when it gave way to outside Walschaerts motion. In Europe, Stephenson gear could be placed either outside the driving wheels and driven by either eccentrics or return cranks or else between the frames driven from the axle through eccentrics, as was the case in Great Britain.
Abner Doble considered Stephenson valve gear: " the most universally suitable valve gear of all, for it can be worked out for a long engine structure or a short one. It can be a simple valve gear and still be accurate, but its great advantage is that its accuracy is self-contained, for the exact relationship between its points of support have but little effect on the motion of the valve, its use on engines in which all the cylinders lie in one plane, represents, in the belief of the writer, the best choice." Another benefit of the Stephenson gear, intrinsic to the system, is variable lead: zero in full gear and increasing as cutoff is shortened. One consequent disadvantage of the Stephenson gear is that it has a tendency to over-compression at the end of the stroke when short cut-offs are used, therefore the minimum cut-off cannot be as low as on a locomotive with Walschaerts gear. Longer eccentric rods and a shorter link reduce this effect. Stephenson valve gear is a convenient arrangement for any engine that needs to reverse and was applied to railway locomotives, traction engines, steam car engines and to stationary engines that needed to reverse, such as rolling-mill engines.
It was used on the overwhelming majority of marine engines. The Great Western Railway used Stephenson gear on most of its locomotives, although the four-cylinder engines used inside Walschaerts gear. Details of the gear differ principally in the arrangement of the expansion link. In early locomotive practice, the eccentric rod ends were pivoted at the ends of the link while, in marine engines, the eccentric rod pivots were set behind the link slot; these became known as the'locomotive link' and the'launch link'. The launch link superseded the locomotive type as it allows more direct linear drive to the piston rod in full gear and permits a longer valve travel within a given space by reducing the size of eccentric required for a given travel. Launch-type links were pretty well universal for American locomotives right from the 1850s but, in Europe, although occurring as early as 1846, they did not become widespread until around 1900. Larger marine engines used the bulkier and more expensive marine double-bar link, which has greater wearing surfaces and which improved valve events by minimising geometric compromises inherent in the launch link.
In the United Kingdom, locomotives having Stephenson valve gear had this mounted in between the locomotive frames. In 1947, the London and Scottish Railway built a series of their Stanier Cl
Erie Railroad
The Erie Railroad was a railroad that operated in the northeastern United States connecting New York City — more Jersey City, New Jersey, where Erie's former terminal, long demolished, used to stand — with Lake Erie. It expanded west to Chicago with its 1941 merger with the former Atlantic and Great Western Railroad known as the New York and Ohio Railroad, its mainline route proved influential in the development and economic growth of the Southern Tier, including cities such as Binghamton and Hornell. The Erie Railroad repair shops were located in Hornell, were Hornell's largest employer. Hornell was where Erie's main line split into two routes, one north to Buffalo and the other west to Cleveland. On October 17, 1960, the Erie merged with the former rival Delaware, Lackawanna & Western Railroad to form the Erie Lackawanna Railroad; the Hornell repair shops were closed, repair operations moved to the Lackawanna's Scranton facility. Much of the former Erie line between Hornell and Binghamton was damaged in 1972 by the floods of Hurricane Agnes, but the damage was repaired and this line is today a key link in the Norfolk Southern Railway's Southern Tier main line.
What was left of the Erie Lackawanna became part of Conrail in 1976. In 1983, Erie remnants became part of New Jersey Transit rail operations, including parts of its Main Line. Today, most of the surviving Erie Railroad routes are operated by the Norfolk Southern Railway; the New York and Erie Rail Road was chartered April 24, 1832 by Governor of New York, Enos T. Throop to connect the Hudson River at Piermont, north of New York City, west to Lake Erie at Dunkirk. On February 16, 1841 the railroad was authorized to cross into the northeast corner of Pennsylvania on the west side of the Delaware River. Construction began in 1836, it opened from Piermont to Goshen on September 23, 1841. After some financial problems, construction resumed in August 1846, the next section, to Port Jervis, opened on January 7, 1848. Further extensions opened to Binghamton December 27, 1848, Owego January 1, 1849, the full length to Dunkirk May 19, 1851. At Dunkirk steamboats continued across Lake Erie to Michigan; the line was built as 6 ft wide gauge.
In 1848 the railroad built the Starrucca Viaduct, a stone railroad bridge over Starrucca Creek in Lanesboro, Pennsylvania which has survived and is still in use today. The viaduct is 100 feet high and 25 feet wide at the top, it is the oldest stone rail bridge in Pennsylvania still in use. The Erie's charter was amended April 8, 1845 to allow the building of the Newburgh Branch, running from the main line near Harriman north-northeast to Newburgh on the Hudson River; the branch opened January 8, 1850. It was used as a connection to the New York and New England Railroad via a car float operation across the river to Beacon, New York; the Paterson and Ramapo Railroad and Union Railroad opened in 1848, providing a connection between the Erie at the village of Suffern in Ramapo and Jersey City, across the Hudson River from New York City. Through ticketing began in 1851, with a required change of cars at Ramapo due to the gauge break. In 1852 the Erie leased the two companies along with the Paterson and Hudson River Railroad, Erie trains begin operating to the New Jersey Rail Road's Jersey City terminal on November 1853 after a third rail for wide gauge was finished.
In 1852 the Buffalo and Rochester Railroad, part of the New York Central Railroad system, completed a new alignment between Buffalo and Batavia. The alignment from Buffalo to Attica was sold to the Erie's Buffalo and New York City Railroad, a reorganization of the Attica and Hornellsville Railroad, converted to the Erie's wide gauge; the extension from Attica southeast to Hornellsville opened on November 17, 1852, giving the Erie access to Buffalo, a better terminal than Dunkirk. The Erie began operating the Chemung Railroad in 1850; the Canandaigua and Elmira Railroad opened in 1851 as a northern extension from Watkins to Canandaigua and was operated by the Erie until 1853. At this point, the Erie subleased the Chemung Railroad to the Elmira; the C&E went bankrupt in 1857 and was reorganized in 1859 as the Elmira and Niagara Falls Railroad, at which time the Erie leased it again. The Chemung Railroad reverted to the Erie in 1858 during the bankruptcy; the Canandaigua and Niagara Falls Railroad continued this line beyond Canandaigua to North Tonawanda with trackage rights over the Buffalo and Niagara Falls Railroad to Niagara Falls and the Niagara Falls Suspension Bridge into Ontario.
This was leased by the Canandaigua and Elmira from its opening in 1853 to 1858, when it went bankrupt, was reorganized as the Niagara Bridge and Canandaigua Railroad, was leased by New York Central Railroad. The NYC blocked the Erie from it; the Erie pushed southward into the coal fields of Elk County, Jefferson County and Clearfield County, Pennsylvania to acquire a source of fuel for its locomotives. This action began with the February 26, 1859 merger of two earlier roads to form the Buffalo and Pittsburgh Railroad Company; the new organization was sponsored by the New York and Erie Railroad Company known as the Erie. The B. B.& P. ran for 25.97 miles through Bradford, Pennsylvania after connecting with the p
NZR OC class
The OC class, built by the Baldwin Locomotive Works for the Wellington and Manawatu Railway in New Zealand, consists of a solitary steam locomotive. Ordered in 1896 as an externally similar but more powerful version of the OA class locomotive ordered in 1894, it entered service in June 1897 as No. 16. It was a Vauclain compound locomotive. In 1908, the WMR and its locomotive fleet was purchased by the New Zealand Railways Department and incorporated into the national rail network, although No. 16 bore a likeness to members of the O class, it was sufficiently different that it warranted separate classification. Technical differences were sufficient. 13/NZR OA 457, accordingly it became OC 458. It is known to have operated on the line from the Hutt Valley through the Rimutaka Range to the western end of the Rimutaka Incline, its final depot was at Cross Creek at the eastern end of the Rimutaka Incline in the Wairarapa, it was withdrawn from service in July 1930. Locomotives of New Zealand Drawing of an OA/OC class locomotive from Derek Brown
Baltimore and Ohio Railroad
The Baltimore and Ohio Railroad was the first common carrier railroad and the oldest railroad in the United States, with its first section opening in 1830. It came into being because the city of Baltimore wanted to compete with the newly constructed Erie Canal and another canal being proposed by Pennsylvania, which would have connected Philadelphia and Pittsburgh. At first this railroad was located in the state of Maryland, with an original line built from the port of Baltimore west to Sandy Hook. At this point to continue westward, it had to cross into Virginia over the Potomac River, adjacent to the confluence of the Potomac and Shenandoah rivers. From there it passed through Virginia from Harpers Ferry to a point just west of the junction of Patterson Creek and the North Branch Potomac River, where it crossed back into Maryland to reach Cumberland. From there it was extended to the Ohio River at Wheeling and a few years also to Parkersburg, West Virginia, it continued to construct lines into Ohio, including a junction at Portsmouth.
In years, B&O advertising carried the motto: "Linking 13 Great States with the Nation." As part of a series of mergers, the B&O is now part of the CSX Transportation network. The B&O included the Leiper Railroad, the first permanent horse-drawn railroad in the U. S. At the end of 1970, the B&O operated 5,552 miles of road and 10,449 miles of track, not including the Staten Island Rapid Transit or the Reading and its subsidiaries, it includes the oldest operational railroad bridge in the United States. When CSX established the B&O Railroad Museum as a separate entity from the corporation, it donated some of the former B&O Mount Clare Shops in Baltimore, including the Mt. Clare roundhouse, to the museum, while selling the rest of the property; the B&O Warehouse at the Camden Yards rail junction in Baltimore now dominates the view over the right-field wall at the Baltimore Orioles' current home, Oriole Park at Camden Yards. Part of the B&O Railroad's immortality has come from being one of the four featured railroads on the U.
S. version of the board game Monopoly. It is the only railroad on the board that did not directly serve New Jersey; the fast-growing port city of Baltimore, Maryland faced economic stagnation unless it opened routes to the western states, as New York had done with the Erie Canal in 1820. On February 27, 1827, twenty-five merchants and bankers studied the best means of restoring "that portion of the Western trade, diverted from it by the introduction of steam navigation." Their answer was to build a railroad—one of the first commercial lines in the world. Their plans worked well, despite many political problems from canal backers and those associated with other railroads; the railroad grew from a capital base of $3 million in 1827 to a large enterprise generating $2.7 million of annual profit on its 380 miles of track in 1854, with 19 million passenger miles. The railroad fed tens of millions of dollars of shipments to and from Baltimore and its growing hinterland to the west, thus making the city the commercial and financial capital of the region south of Philadelphia.
Two men — Philip E. Thomas and George Brown — were the pioneers of the railroad, they spent the year 1826 investigating railway enterprises in England, which were at that time being tested in a comprehensive fashion as commercial ventures. Their investigation completed, they held an organizational meeting on February 12, 1827, including about twenty-five citizens, most of whom were Baltimore merchants or bankers. Chapter 123 of the 1826 Session Laws of Maryland, passed February 28, 1827, the Commonwealth of Virginia on March 8, 1827, chartered the Baltimore and Ohio Rail Road Company, with the task of building a railroad from the port of Baltimore west to a suitable point on the Ohio River; the railroad, formally incorporated April 24, was intended to provide a faster route for Midwestern goods to reach the East Coast than the hugely successful but slow Erie Canal across upstate New York. Thomas was elected as Brown the treasurer; the capital of the proposed company was fixed at five million dollars, but the B&O was capitalized in 1827 with a three million dollar issue of stock.
Every citizen of Baltimore owned a share, as the offering was oversubscribed. Construction began on July 4, 1828, when Charles Carroll of Carrollton performed the groundbreaking by laying the cornerstone; the initial tracks were built with granite stringers topped by strap iron rails. The first section, from Baltimore west to Ellicott's Mills, opened on May 24, 1830. A horse pulled the first cars 26 miles and back, since the B&O did not decide to use steam power for several years. Railroad men in South Carolina had earlier commissioned a steam locomotive from a New York foundry, while the B&O was still experimenting with horse power and sails; the B&O's first locomotive, the "Tom Thumb", was made in America and would pull passenger and freight cars at 18 miles per hour. Developers decided to follow the Patapsco River to a point near Parr's Ridge, where the railroad would cross a height of land and descend into the valley of the Monocacy and Potomac rivers. Further extensions opened to Frederick on December 1, 1831.
The connection to the Winchester and Potomac Railroad at Harpers Ferry opened in 1837 the line to Martinsburg in May 1842.
Walschaerts valve gear
The Walschaerts valve gear is a type of valve gear invented by Belgian railway mechanical engineer Egide Walschaerts in 1844 used to regulate the flow of steam to the pistons in steam engines. The gear is sometimes named without the final "s", since it was incorrectly patented under that name, it was extensively used in steam locomotives from the late 19th century until the end of the steam era. The Walschaerts valve gear was slow to gain popularity; the Stephenson valve gear remained the most used valve gear on 19th-century locomotives. However, the Walschaerts valve gear had the advantage that it could be mounted on the outside of the locomotives, leaving the space between the frames clear; the first locomotive fitted with the Walschaerts valve gear was built at the Belgian Tubize workshops, was awarded a gold medal at the 1873 Universal Exhibition in Vienna. In 1874 New Zealand Railways ordered two NZR B class locomotives, they were Double Fairlie locomotives, supplied by Avonside. They were Cape gauge.
The Mason Bogie, a modified Fairlie locomotive of 1874, was the first to use the Walschaerts gear in North America. The first application in Britain was on a Single Fairlie 0-4-4T, exhibited in Paris in 1878 and purchased by the Swindon and Andover Railway in March 1882. According to Ahrons, the locomotive saw little service as nobody seems to have known how to set the valves and this led to enormous coal consumption. In the 20th century, the Walschaerts valve gear was the most used type on larger locomotives. In Europe, its use was universal, whilst in North America, the Walschaerts gear outnumbered its closest competitor, the derived Baker valve gear, by a wide margin. In Germany and some neighbouring countries, like Poland and Czechoslovakia, the Walschaerts gear is named the Heusinger valve gear after Edmund Heusinger von Waldegg, who invented the mechanism independently in 1849. Heusinger's gear was closer to the form adopted, but most authorities accept Walschaerts' invention as sufficiently close to the final form.
The Walschaerts valve gear is an improvement on the earlier Stephenson valve gear in that it enables the driver to operate the steam engine in a continuous range of settings from maximum economy to maximum power. At any setting, the valve gear satisfies the following two conditions: The valve opens to admit steam to the cylinder just before the start of a piston stroke; the pressure of this steam provides the driving force. Soon before the space on one side of the piston starts to contract, the valve starts to release steam from that space to the atmosphere, so as not to impede the movement of the piston. In an economical setting, steam is admitted to the expanding space for only part of the stroke. Since the exhaust is shut, during the rest of the stroke the steam that has entered the cylinder expands in isolation, so its pressure decreases. Thus, the most energy available from the steam is used; the Walschaerts valve gear enables the engineer to change the cutoff point without changing the points at which intake starts.
Economy requires that the throttle be wide open and that the boiler pressure is at the maximum safe level to maximise thermal efficiency. For economy, a steam engine is used of a size such that the most economical settings yield the right amount of power most of the time, such as when a train is running at steady speed on level track; when greater power is necessary, e.g. when gaining speed when pulling out of a station and when ascending a gradient, the Walschaerts valve gear enables the engineer to set the cutoff point near the end of the stroke, so that the full pressure of the boiler is exerted on the piston for the entire stroke. With such a setting, when the exhaust opens, the steam in the cylinder is near full boiler pressure; the pressure in the steam at that moment serves no useful purpose. This sudden pulse of pressure causes the loud “choo” sound that members of the public associate with steam engines, because they encounter engines at stations, where efficiency is sacrificed as trains pull away.
A steam engine well adjusted for efficiency makes a soft “hhHHhh” sound that lasts throughout the exhaust stroke, with the sounds from the two cylinders overlapping to produce a nearly constant sound. The valve gear operation combines two motions; the secondary is the directional/amplitude motion, imparted at the top. Consider that the driver has adjusted the reversing lever such that the die block is at mid-gear. In this position the secondary motion is eliminated and the piston valve travel is shortest, giving minimal injection and exhaust of steam; the travel of the piston valve is twice the total of lap plus lead. Contrast this to when the die block is at the bottom of the expansion link, giving maximum steam injection and exhaust; this is used in accelerating forward from rest. Conversely when the die block is at the top of the expansion link, maximal power in reverse is obtained. Once the locomotive has accelerated the driver can adjust the reverser toward the mid-gear position, decreasing cut-off to give a more economical use of steam.
The engine's tractive e
