| Coupling (railway) |
Article Index for Coupling |
Website Links For Coupling |
Information AboutCoupling (railway) |
|
coupling]] A coupling (or a '''coupler''') is a mechanism for connecting Railway cars in a train. The design of these couplings is a standard almost as important as the Railway Gauge , since flexibility and convenience are maximised if the couplings can work together no matter what order they come in. BUFFERS AND CHAIN The type of coupling established as standard on railways following the British tradition is the Buffers and chain coupling found on the pioneering Liverpool And Manchester Railway of 1830 . These couplings followed earlier Tram way practice but were made more regular. The cars are coupled by hand using hook and link system with a Turnbuckle -like device that draws the cars together. In Britain, this is called a Screw coupling. Cars have Buffers , one at each corner on the ends, which are pulled together and compressed by the coupling device. This arrangement limits the slack in trains and lessens shocks. In contrast the Janney Coupler s encourage violent encounters in order to engage the coupling fully. The earliest buffers were fixed, being extensions of the frames of the wagons, but later on, spring buffers were introduced. Not only inefficient and slow, the European hand-coupled system is relatively unsafe for the rail workers because they are easily squashed between the buffers. With central couplers (except link and pin) it is not usually necessary to get between the cars for coupling or uncoupling. The safety issue was one of the main arguments for changing to central couplers. But even after over 30 years, the change has still not been completed. This coupling type is the standard in the European countries, except the former Soviet Union (those countries have the SA-3 automatic coupler). The coupling and uncoupling of this coupler is provided by a worker, who must climb between the cars. First he must turn a little with releasing screw (it is only an aid with two opposite windings, and it does not uncouple the train itself) to the loose position, and than he can hang off or on the chain from/to the hook. After hanging on to the towing hook the realising screw must be turn a little to the tight position. When the coupler is idle, it must be hanged up to the idle hook in order, to prevent from the damage itself or the brake pipes. Only shunting is permitted with an unhanged coupler. The idle brake pipes must be hanged up too. (On the picture you can see two coupled cars for ride, with single brake pipe). The hooks and chain hold the carriages together, while the buffers keep the carriages from banging into each other so that no damage is caused. The buffers can be "dumb" or spring-loaded, or indeed a mixture. That means there is no run in forces on the coupler. The other plus against the automatic coupler is it's slack that cause less forces in the curves, the coupler break in the curves has a less probability, than at the automatic coupler. The minus is the less amount of the freight, that could be hauled by that coupler (max. 3000 metric tones). Early rolling stock was often fitted with a pair of auxiliary chains, as a backup if the main coupling were to fail. This made sense before the fitting of continuous and failsafe braking systems, whether air- or vacuum-based. On railways where rolling stock always pointed the same way, the chain might be mounted at one end only, as a small cost- and weight-saving method. On German Railways , one buffer is flatter than the other buffer which is slightly more rounded. This provides better contact between the buffers than would be the case if both buffers were slightly rounded. Three link couplings A peculiarly British institution was the "loose-coupled" freight train. This used three-link couplings with no means of drawing the wagons together so they banged into each other when the locomotive's brakes were applied. Such trains were limited to 25 miles per hour. A slight improvement on this was the "Instanter" coupling, in which the middle link of a three link chain is specially shaped so that when lying "prone" it provides enough slack to make coupling possible, but when this middle link is rotated 90 degrees, the length of the chain is effectively shortened, reducing the amount of slack, without the need to wind a screw. This variation is used only on freight wagons. Problems with buffers and chain The buffers and chain coupling system has a maximum load much less that the Janney coupling. Also, on sharp reverse curves, the buffers can get bufferlocked by somehow getting on the wrong side of the adjacent buffer. An accident at a Swiss station was caused by bufferlocked wagons in the 1980s. The bufferlock could be caused on the very sharp turnouts by the older rounded buffers. The newer buffers has rectangle shape and they are wider than taller. They are not so flat, they could cause bufferlocking rarely. Variation with gauge The distance between the buffers tends to increase as the gauge increases, so that if wagons are changed from one gauge to another, the buffers will no longer match. This occurs because the buffers are originally extensions of the frames, which are spaced according to the gauge. On some narrow-gauge lines in Europe , a simplified version is used, consisting of a single central buffer with a chain underneath. The chain usually contains a screw-adjustable link to allow close coupling. On sharp curves, a single centre buffer is less likely to be subject to buffer locking problem, as described above. Dual coupling It is possible to mount both buffers and chain and knuckle couplers on the same car, provided that one can swing out of the way. Locomotives as well as some freight cars of the Indian Railways are fitted with a 'transition coupler' that incorporates a screw coupling within a knuckle coupler. However, the knuckle coupler remains in position and does not swing away when not in use. The screw coupling is mounted on a lug within the knuckle coupler. Example: SAB WABCO C-AK Most Indian freight cars use the knuckle coupler alone, without buffers, whereas passenger coaches almost exclusively use screw couplers and buffers. Exceptions are the new LHB coaches imported from Europe, and a few other makes of carriages converted to use knuckle couplers. [http://irfca.org/faq/faq-stock2.html] Some Russian locomotives and wagons have buffers together with the central coupler. When coupling to Finnish equipment, a short chain with a block that fits in the central coupler is placed on the Russian side, backs up and compresses the buffers so that you can lay the chain on the hook. (That is also the common way of coupling locomotives to or from wagons. Doing it that way is faster than unscrewing the link.) LINK AND PIN (381 Mm ) Gauge Speeder .]] The link and pin coupling was the original style of coupling used on American railways, surviving after conversion to Janney couplings on forestry railways. While simple in principle, the link and pin coupling suffered from a lack of standardisation regarding size and height of the links. The link and pin coupler consisted of a tubelike body that received an oblong link. During coupling, a railworker had to stand between the cars as they came together and guide the link into the coupler pocket. Once the cars were joined, the employee inserted a pin into a hole a few inches from the end of the tube to hold the link in place. This procedure was exceptionally dangerous and many brakemen lost fingers or entire hands when they did not get their hands out of the way of the coupler pockets; many more were killed as a result of being crushed between cars or dragged under cars that were coupled too quickly. Brakemen were issued with heavy clubs that could be used to hold the link in position, but many brakemen would forgo the club's use and risk injury. The link and pin coupler ultimately proved unsatisfactory because:
An episode of the 1960s TV series '' Casey Jones '' was devoted to the problems of link and pin couplings. MEATCHOPPER Alco at the Ffestiniog Railway ]] Meatchopper (also known as ''Norwegian'') couplings consist of a central buffer with a mechanical hook that drops into a slot in the central buffer. The hook resembles a meat chopper, hence the name. The meatchopper is found only on Narrow Gauge Railway s, such as the Ffestiniog Railway and the Welsh Highland Railway , where low speeds and reduced train loads allow a simpler system. On railway lines where rolling stock always points the same way, the mechanical hook may be provided only on one end of each wagon. This was the situation on the Lynton & Barnstaple (L&B), a narrow gauge line in Devon , England . Similarly, the hand brake handles may also be on one side of the wagons only. Meatchopper couplings are not particularly strong, and may be supplemented by auxiliary chains. The L&B originally used side chains in conjunction with Norwegian couplers, but these were found to be unnecessary with the slow speeds employed (10-15 miles per hour) and were removed within a year or so of the line opening in 1898 . The Pichi Richi Railway in South Australia uses meatchopper couplers as its standard, and converts Janney coupler to meatchopper as required. The slot in the "buffer beam" where the coupler protrudes appears to be about the same for both types of couplers. As a museum, it is appropriate to use the older type of coupling. Not all meatchopper couplings are compatible with one another as they vary in height, width, and may or may not be limited to one hook at a time. AUTOMATIC COUPLERS There are a number of automatic train couplings, most of which are mutually incompatible.
Janney coupler Later Master Car Builders Association coupler, now '''AAR ( American Association Of Railroads ) coupler''', see also '''AAR coupler''' above. .]] Janney couplings are always righthanded. The knuckle coupler (or '''Janney coupler''') was invented by ''' Eli H. Janney ''', who received a Patent in 1873 (). It is also known as a "buckeye coupler", notably in the United Kingdom , where some rolling stock (mostly for passenger trains) is fitted with it. Janney was a dry goods clerk and former Confederate Army officer from Alexandria, Virginia , who used his lunch hours to whittle from wood an alternative to the '''link and pin coupler'''. In 1893 , satisfied that an automatic coupler could meet the demands of commercial railroad operations and, at the same time, be manipulated safely, the United States Congress passed the Safety Appliance Act . Its success in promoting switchyard safety was stunning. Between 1877 and 1887, approximately 38% of all railworker accidents involved coupling. That percentage fell as the railroads began to replace link and pin couplers with automatic couplers. By 1902 , only two years after the SAA's effective date, coupling accidents constituted only 4% of all employee accidents. In absolute numbers, coupler-related accidents dropped from nearly 11,000 in 1892 to just over 2,000 in 1902, even though the number of railroad employees steadily increased during that decade. When the Janney coupling was chosen to be the American standard, there were an amazing 8000 patented alternatives to choose from. The only significant defect of the AAR (Janney) design is that sometimes the drawheads need to be manually aligned. Changes since 1873 The AAR coupler, originally called the Janney coupling, has stood the test of time since its invention, and has seen only minor changes:
FULLY AUTOMATIC COUPLINGS Fully automatic couplings are those which make all connections between the rail vehicles (mechanical, air brake and electrical) without human intervention, in contrast to autocouplers which just handle the mechanical aspects. The majority of trains fitted with these types of couplers are multiple units, especially those used in Mass Transit operations. There are a few designs of fully automatic couplers in use worldwide, including the Scharfenberg coupler, various knuckle hybrids (such as the Tightlock, used in the UK), the wedgelock coupling, Dellner couplings (similar to Scharfenberg couplers in appearance), and the BSI coupling. Older US transit operators use non-Janney electro-pneumatic coupler designs that have been in service for decades. |
Image:Northern-321901-coupling-02jpgAPTA, Type "H",
| "http://wwwinformationdelightinfo/information/entry/Tightlock_coupling" class="copylinks">Tightlock Coupling |
|
|
|