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A buffer is a part of the buffers-and-chain coupling system used on the railway systems of many countries, among them most of those in Europe, for attaching railway vehicles to one another (in North America, rolling stock instead has draft gear built into the couplers).
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Fitted at the ends of the vehicle frames on the buffer beam, one at each corner, the buffers are projecting, shock-absorbing pads which, when vehicles are coupled, are brought into contact with those on the next vehicle. The buffer itself comprises the buffer plates which take the impact.
The draw chain used between each pair of vehicles includes a screw which is tightened after coupling to shorten the chain and keep the buffers pressed together. Such is known as a 'screw coupling'. Historically, coupling chains were no more than that, a short length of heavy chain (typically three links long) with no adjustment. These would result in a 'loose-coupled train' in which the buffers of adjacent vehicles would only touch when the coupling chain was fully slack, such as when being pushed or going down hill.
The buffers in the very earliest days of railways were rigid dumb buffers made of wooden blocks with a metal cap at the end. For example, Germany's first commercially successful locomotive, the Adler, built in 1835, had wooden buffers.
In the 1830s the first spring-loaded buffers were introduced on the Liverpool & Manchester Railway and during the mid-19th century sprung buffers were fitted to all coaches and wagons. [2]
The original English buffer plates were the same on each side, so that there was an occasional tendency for them to slide off each other and become locked. German railway buffer plates are flat on one side and convex on the other to reduce this tendency to slide off. [1]
The rod buffer was the earliest German type of sprung buffer. The first ones consisted of a steel rod that carried the buffer plate at one end. The buffer rod pushed backwards on a spiral volute spring (coil spring), which was supported by a strong sheet metal cylindrical sleeve. Compressing the spring absorbed the impact. The first spring-loaded buffers were invented by John Baillie in 1846. [3]
Rod buffers can only be found on museum vehicles in Europe today. They are still common in Argentina.
Since the relatively thin buffer rods often bent during operation and caused major damage in accidents, the German state railways developed the plunger buffer. The buffer plate sits on a steel tube with a larger diameter, which is therefore more resistant to bending.
The volute spring system initially still used for the plunger buffers had the disadvantage that the energy put into compression was completely released again, so that the vehicles were pushed apart again after the impact. This required trains to be braked evenly and, above all, not just at certain points in order to avoid oscillations in the train set, which inter alia can cause the couplings to break. An improvement was made by using ring springs , as these convert most of the input energy into frictional heat.
With centre buffer couplings, the tasks of buffers are usually transferred to the coupling elements, which are designed to be correspondingly stable and are mounted with interposed spring elements within the vehicle frame instead of on a buffer beam. They are often used on narrow gauge railways and funiculars.
The buffers fitted to modern locomotives and rolling stock incorporate oleo-pneumatic shock absorbers.
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In the early days of the railway, each railway company determined the positioning and arrangement of the couplings and buffers at its own discretion. But once the railway network began to develop from the first independently built routes, this hampered the transfer of wagons. Railway vehicles that were to be transferred to other parts of the network, run by other companies, had to be equipped with several buffers or coupling systems. Founded in 1882, the International Conference for Promoting Technical Uniformity on Railways specified the dimensions for buffer positions and distances customary in England and northern Germany as a standard.
Spain was an exception for a long time. A buffer separation of 1,950 mm was specified there because of the force transmitted to the longitudinal beams of the wagons, which are further apart due to their broad gauge railways. Wagons that were designed for transit were therefore given wider buffer plates. Spain's conversion to the international standard took place up to the 1990s. Extra-wide buffer plates are still common in Spain, and French Corail wagons were also equipped with them. The wider buffer spacing is also common on the broad gauge networks of Portugal, India, Pakistan, Bangladesh and Sri Lanka, and Argentina. Due to the lower throughput of Portuguese wagons into the standard gauge network, extra-wide buffer plates are less common in Portugal. Passenger coaches for long-distance traffic were almost completely equipped with them. As a result of railway stock sales, locomotives and wagons with extra-wide Iberian buffers also reached Argentina.
Standardised buffers are used by European railway companies:
The aforementioned UIC leaflets were replaced by the EN 15551 standard after the introduction of the TSI Interoperability Guidelines.
In many cases, the buffer on the left-hand side in the direction of travel was designed with a flat plate, and the one on the right with a curved plate, so that a flat plate and a curved plate always meet, thereby avoiding edge pressure.
According to the 1961 UIC regulations, all vehicles in Europe were to be equipped with buffer plates that were curved on both sides but much flatter. The radius of the buffer curvature is 1,500 mm for passenger coaches and 2,750 mm for freight wagons built from 1994. Round buffer plates with a diameter of 340, 370, 450 or 500 mm are common on freight wagons. Rectangular plate shapes are generally used for passenger coaches and locomotives, with the edge nearer the longitudinal centre of the vehicle being bevelled on passenger coaches due to the space required by the coach gangways. There are also buffer plates of other shapes and widths, with the height between the upper and lower horizontal edge being between 340 and 360 mm. According to EN 15551, the standardised widths for freight wagon buffers are 450 or 550 mm, for Spain 550 or 650 mm with a height of 340 mm. For passenger coaches, the buffer plate widths are between 600 and 720 mm, depending on the vehicle geometry. Buffers with non-circular buffer heads cannot be rotated in any case.
The remaining free space between the vehicles is referred to as the Berne Space (Berner Raum)
A British specialty are pull-out buffers on passenger coaches and locomotives with hinged central buffer couplings of the Janney design. If similar vehicles are connected using these central buffer couplings, the buffers are pushed in and ineffective. For coupling vehicles that are only equipped with screw couplings, the buffers are pulled out and locked in this position with locking pieces.
Dead-end sidings are often fitted with buffer stops to prevent vehicles running off the end of the track. These may consist of a simple transverse beam fixed at buffer height but the buffer stops at passenger stations can be elaborate hydraulic installations capable of absorbing a considerable amount of energy.
Friction buffer stops are clamped 'loosely' to the rails, and when hit by a train that fails to stop correctly, move with the train for perhaps 30 m (98 ft) scraping the top of the rails, which absorbs considerable energy.
In violent collisions, the buffers of adjacent carriages may become displaced relative to one another, allowing the carriages to telescope which is very dangerous. The risk of this can be reduced if the buffers (or fake buffers) have corrugations that grip each other and prevent the buffers becoming displaced and so leading to telescoping.
Brake van and guard's van are terms used mainly in the UK, Ireland, Australia and India for a railway vehicle equipped with a hand brake which can be applied by the guard. The equivalent North American term is caboose, but a British brake van and a caboose are very different in appearance, because the former usually has only four wheels, while the latter usually has bogies. German railways employed brakeman's cabins combined into other cars.
A loading gauge is a diagram or physical structure that defines the maximum height and width dimensions in railway vehicles and their loads. Their purpose is to ensure that rail vehicles can pass safely through tunnels and under bridges, and keep clear of platforms, trackside buildings and structures. Classification systems vary between different countries, and gauges may vary across a network, even if the track gauge is uniform.
On a steam locomotive, a driving wheel is a powered wheel which is driven by the locomotive's pistons. On a conventional, non-articulated locomotive, the driving wheels are all coupled together with side rods ; normally one pair is directly driven by the main rod which is connected to the end of the piston rod; power is transmitted to the others through the side rods.
The British Rail Class 73 is a British electro-diesel locomotive. The type is unusual in that it can operate from the Southern Region's 650/750 V DC third-rail or an on-board diesel engine to allow it to operate on non-electrified routes. This makes it very versatile, although the diesel engine produces less power than is available from the third-rail supply so the locomotives are rarely operated outside of the former Southern Region of British Rail. It is one of the first bi-mode locomotives ever built. Following the withdrawal and scrapping of the more powerful Class 74 bi-mode locomotives in 1977, the Class 73 was unique on the British railway network until the introduction of the Class 88 bi-mode locomotives in 2017. Ten locomotives have been scrapped.
A coupling or coupler is a mechanism, typically located at each end of a rail vehicle, that connects them together to form a train. The equipment that connects the couplers to the vehicles is the draft gear or draw gear, which must absorb the stresses of the coupling and the acceleration of the train.
A railway brake is a type of brake used on the cars of railway trains to enable deceleration, control acceleration (downhill) or to keep them immobile when parked. While the basic principle is similar to that on road vehicle usage, operational features are more complex because of the need to control multiple linked carriages and to be effective on vehicles left without a prime mover. Clasp brakes are one type of brakes historically used on trains.
A transporter wagon, in railway terminology, is a wagon (UIC) or railroad car (US) designed to carry other railway equipment. Normally, it is used to transport equipment of a different rail gauge. In most cases, a transporter wagon is a narrower gauge wagon for transporting a wider gauge equipment, allowing freight in a wider gauge wagons to reach destinations on the narrower gauge network without the expense and time of transshipment into a narrower gauge wagons.
Co-Co is the wheel arrangement for diesel and electric locomotives with two six-wheeled bogies with all axles powered, with a separate traction motor per axle. The equivalent UIC classification (Europe) for this arrangement is Co′Co′, or C-C for AAR.
A variable gauge system allows railway vehicles in a train to travel across a break of gauge between two railway networks with different track gauges. For through operation, a train must be equipped with special bogies holding variable gauge wheelsets which contain a variable gauge axle (VGA).
SA3 couplers or Willison coupler and Russian coupler are railway couplings used primarily in Russia and states influenced by the former Soviet Union, such as Finland, Poland, and Mongolia.
The railcar couplers or couplings listed, described, and depicted below are used worldwide on legacy and modern railways. Compatible and similar designs are frequently referred to using widely differing make, brand, regional or nick names, which can make describing standard or typical designs confusing. Dimensions and ratings noted in these articles are usually of nominal or typical components and systems, though standards and practices also vary widely with railway, region, and era. Transition between incompatible coupler types may be accomplished using dual couplings, a coupling adapter or a barrier wagon.
A barrier vehicle (BV), barrier wagon, match wagon or translator coach is used to convert between non-matching railway coupler types. This allows locomotives to pull railway vehicles or parts of a train with a different type of coupler. A match wagon has an identical dual coupling at both ends.
A covered goods wagon or van is a railway goods wagon which is designed for the transportation of moisture-susceptible goods and therefore fully enclosed by sides and a fixed roof. They are often referred to simply as covered wagons, and this is the term used by the International Union of Railways (UIC). Since the introduction of the international classification for goods wagons by the UIC in the 1960s a distinction has been drawn between ordinary and special covered wagons. Other types of wagon, such as refrigerated vans and goods wagons with opening roofs, are closely related to covered wagons from a design point of view. Similar freight cars in North America are called boxcars.
Janney couplers are a semi-automatic form of railway coupling that allow rail cars and locomotives to be securely linked together without rail workers having to get between the vehicles. They are also known as American, AAR, APT, ARA, MCB, knuckle, Buckeye, tightlock, Henricot or Centre Buffer Couplers.
A Norwegian coupling or coupler, is a manually operated coupling at each end of some narrow-gauge railway rolling stock. It consists of a central buffer incorporating a hook that drops into a slot in the opposing central buffer. The system is only found on narrow gauge railways with a gauge of 1067 mm or less on which low speeds and train loads allow a simpler system than, for example, knuckle couplers. Norwegian couplings are not particularly strong, and may be supplemented by auxiliary chains. Not all Norwegian couplings are compatible with one another since they vary in height and width. Some may permit a hook from both rail vehicles to be in place; others may be limited to one.
From time to time, a railway decides that it needs to upgrade its coupling system from one that is proving unsatisfactory, to another that meets future requirements. This can be done gradually, which can create many problems with transitional incompatibilities, or overnight, which requires much planning.
Buffers and chain couplers are the de facto International Union of Railways (UIC) standard railway coupling used in the EU and UK, and on some surviving former colonial railways, such as in South America and India, on older rolling stock. Buffers and chain couplers are an assembly of several devices: buffers, hooks and links, or turnbuckle screws.
Different types of railroad rolling stock have different couplers depending on the purpose and type of equipment being used and its intended destination. European rolling stock tend to use buffers and chain couplers while American rolling stock uses a Janney coupler or "knuckle coupler". These are incompatible with each other, but where some railroads have obtained older, less expensive used rolling stock from different countries or regions, instead of having to standardize on one form of coupler, it may be useful to be able to use either type of coupler on a piece of rolling stock without having to remove anything.
The balance lever coupling, also known as rocking lever coupling or compensating coupling, is a type of central buffer coupling that has found widespread use, especially in narrow-gauge railways. In Switzerland this type of coupling is called a central buffer with two screw couplings, abbreviated to Zp2, or referred to as a central buffer coupling with coupling hooks on the side
A pocket wagon is a freight wagon that has been specially designed for the transport of truck semi-trailers. This wagon belongs to the group of flat wagons in special design with bogies and is used in combined transport (CT). The name of these freight wagons comes from the fact that between the narrow longitudinal girders on the outside and also lengthways between the bogies, the so-called pockets are located, in which the wheels of the semi-trailers are particularly low. For flexible use in CT, pocket wagons have hinged latches with ISO spigots on the solebar, so that containers and swap bodies up to 45 ft can be accommodated. As a flat wagon, it bears the UIC generic letter S and, since it is intended for the transport of road vehicles on one level, the code letter d. Since it is also possible to transport containers in a pocket wagon, it bears the UIC generic mark Sdgs. In this context, the code letter g stands for "containers up to 60 feet" and the lower case s for the permitted speed of up to 100 km/h (62 mph). The wagons have a yellow triangle with a black P on the long side. The first pocket wagons were built in Germany as early as 1972 and further developed according to requirements.