   #copyright

Coupling (railway)

2007 Schools Wikipedia Selection. Related subjects: Railway transport

   Knuckle (AAR Type "E") couplers in use.
   Enlarge
   Knuckle (AAR Type "E") couplers in use.

   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.

   For a complete list of what railway uses which coupler see (JANE'S
   WORLD RAILWAYS)

Buffers and chain

   Traditional buffer-and-chain coupler
   Enlarge
   Traditional buffer-and-chain coupler
   Two cars coupled
   Enlarge
   Two cars coupled
   Buffer and chain coupler with knuckle swung out of the way.
   Enlarge
   Buffer and chain coupler with knuckle swung out of the way.

   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 tramway 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. 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 couplers (see below) 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.

   Although inefficient and slow, the European hand-coupled system is
   relatively safe for the rail workers because the buffers prevent them
   from being crushed between the cars.

   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.

   Early rolling stock was often fitted with a pair of auxiliary chains,
   as a backup if the main coupling were to fail. This would have 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

   It is possible to make the buffer and chain coupler close up to a tight
   fit, without the need to wind a screw. 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. 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.

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.

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. 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 rakes of
   carriages converted to use knuckle couplers.

Link and pin

   The coupler pocket (just below the two lights) for a link and pin
   coupler on a 15 inch gauge speeder.
   Enlarge
   The coupler pocket (just below the two lights) for a link and pin
   coupler on a 15  inch 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 didn't 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:
     * It made a loose connection between the cars, with too much slack
       action.
     * There was no standard design, and train crews often spent hours
       trying to match pins and links while coupling cars.
     * The links and pins were often pilfered (due to their value as scrap
       metal), resulting in substantial replacement costs. John H. White
       suggests that the railroads considered this to be more important
       than the safety issue at the time (see reference below).
     * Crew members had to go between moving cars during coupling, and
       were frequently injured and sometimes killed.
     * Railroads wished to operate trains that were heavier than the link
       and pin system could cope with.

   An episode of the 1960s TV series Casey Jones was devoted to the
   problems of link and pin couplings.

Meatchopper

   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 railways, 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.

   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.
   Fortunately, the slot in the "buffer beam" where the coupler sticks out
   appears to be about the same for both types of couplers. As a museum,
   it is appropriate to use the more old-fashioned type of coupling.

   Not all meatchopper couplings are compatible with one another.

Buffer and chain

   A simplified coupling found on some narrow-gauge lines in Europe
   consists of a single central buffer with a chain underneath. The chain
   usually contains a screw-adjustable link to allow close coupling.

Automatic couplers

   There are a number of automatic train couplings, most of which are
   mutually incompatible.
     * AAR ( American Association of Railroads) coupler (also known as
       knuckle coupler and once known as Janney coupler, see below) used
       in Canada, the USA, Mexico, Japan, Australia, South Africa, Saudi
       Arabia, Cuba, Chile, Brazil, China and elsewhere.
          + Maximum tonnage as high as 30,000 t.
          + The AAR coupling comes in at least two sizes, "full size" and
            "three quarter" which are not compatible. Lighter weight
            railways, especially those of narrow gauge, with no need for
            interrunning, sometimes use smaller (3/4 or half size)
            versions of the AAR coupling. AAR (Janney) couplings are
            always righthanded.
          + The AAR couplers (or Janney couplings) are not necessarily
            mounted at the same height above rail, but within reason, this
            can be tolerated.
          + Uncoupling AAR couplers is done by lifting the coupling pin
            with a lever located at the corner of the railway car. This
            pin is locked when the coupler is under tension, so the usual
            uncoupling steps are to compress the coupling with a
            locomotive, lift and hold up the pin, then pull the cars
            apart. A side operated variant is called the "Sharon coupler".
          + Trains fitted with AAR couplers can have heavier loads than
            any other type of coupler. Thus the heaviest coal trains in
            New Zealand have AAR couplings even though the remainder of
            the fleet has the meatchopper kind. Also, long-distance
            freight trains in North America are quite commonly more than a
            mile (1.6 km) long, whereas this is unknown in Europe, where
            most freight trains still use the buffers and chain system.
          + See also "Janney Coupler" and "changes since 1873" below.
     * Russian SA3 coupler , also known as a " Willison Coupler with a
       Russian contour", (somewhat similar to Janney) used in Russia,
       former Soviet Union, Finland, Mongolia and Iraq. See also:
       Animation showing SA3 coupling (site only in Russian)
          + Maximum tonnage about 6,000 t.
     * European proposal coupler, (compatible with the Russian coupler)
       with automatic air, control and power connections. Implementation
       permanently delayed except for a few users.
     * Scharfenberg coupler used on electric trains - connects brake and
       controls. See Fully Automatic Couplings below.
          + Maximum tonnage about 1,000 t.
     * Note: There exist a number of other automatic train couplings
       similar to the Scharfenberg coupler, but not necessarely compatible
       with it. Older US transit operators continue to use these
       non-Janney electro-pneumatic coupler designs and have used them in
       service for decades.

Janney coupler

   Later Master Car Builders Association coupler, now AAR ( American
   Association of Railroads) coupler, see also AAR coupler above.
   Diagram of the top view of Janney's coupler design as published in his
   patent application in 1873.
   Enlarge
   Diagram of the top view of Janney's coupler design as published in his
   patent application in 1873.

   Janney couplings are always righthanded.

   The knuckle coupler (or Janney coupler) was invented by Eli H. Janney,
   who received a patent in 1873 ( U.S. Patent 138,405). It is also known
   as a "buckeye coupler", notably in the United Kingdom, where some
   rolling stock 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:
     * Type "E" coupler, the original (plain) AAR coupler, derived from
       the Master Car Builders Association coupler.
     * Type "F" coupler, a "Tooth and socket" variation to prevent
       accidents, derailments and wrecks from uncoupling the couplers. The
       "tooth" on a loose coupler could puncture any tank car or other car
       carrying hazardous materials. Variations on the AAR type "F"
       coupler have been devised to provide extra protection, in case of
       derailments and train wrecks, to cars routinely carrying sensitive
       or hazardous loads. These variations of type "F" couplers,
       generally involving "shelves", remain fully compatible with
       standard AAR couplers, but tend to keep derailments and collisions
       from uncoupling the cars (thereby preventing the "tooth" of the
       couplers from piercing the ends of the cars).
     * The APTA (former AAR) standard type "H" coupler, a "Tooth and
       socket" variation used mostly, if not exclusively, on passenger
       cars. Types "F" and "H" couplers are also known as tightlock
       couplings. The Type "H" coupler is now under the supervision of the
       APTA ( American Public Transportation Association)
     * "pads" to reduce slack on passenger trains.
     * improvement to castings, etc. to increase maximum trailing load.
     * rotating-shaft couplers (type "F") introduced for use in rotary car
       dumpers
     * It is clear that the original Janney coupler is no longer
       compatible with the latest AAR couplers. A visual comparison
       between the original Janney contour and the current AAR contour
       (see the illustration of the "Diagram of the top view of Janney's
       coupler..." and the photograph of the "Knuckle couplers in use"
       elsewhere in this article) would stongly indicate that the original
       Janney contour and the current AAR contour (especially that of the
       knuckle itself) are no longer compatible. The current AAR contour
       dates back to the " Master Car Builders Association" coupler.
     * narrow gauge railways such as the Victorian Puffing Billy Railway
       use a miniature version of the AAR coupler.

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.

   Dellner

            Scharfenberg

                        BSI

                           APTA, Type "H", Tightlock coupling

   Wedgelock

Scharfenberg Coupler

   Scharfenberg coupler
   Enlarge
   Scharfenberg coupler

   The Scharfenberg coupler or Scharfenbergkupplung or "Schaku" is
   probably the most commonly used type of fully automatic couplings.
   Originating in Europe, it has gradually spread from transit trains to
   regular passenger service trains, although, outside of Europe, its use
   is generally restricted to mass transit systems. The Schaku coupler is
   superior in many ways to the AAR (Janney/Knuckle) coupler because it
   makes the electrical and also the pneumatic connections and
   disconnections automatic. However there is no standard for the
   placement of these electro-pneumatic connections. Some rail companies
   have them placed on the sides while others have them placed above the
   mechanical portion of the Schaku coupler. The main disadvantage to the
   Scharfenberg coupler is its low maximum tonnage, which makes it totally
   unsuitable for freight operations.

   Small air cylinders, acting on the rotating heads of the coupler,
   ensure the Schaku coupler engagement, making it unnecessary to use
   shock to get a good coupling. Joining portions of a passenger train can
   be done at very low speed (less than 2 mph [or 3.2km/h] in the final
   approach), so that the passengers are not jostled about. Rail equipment
   manufacturers such as Bombardier offer the Schaku coupler as an option
   on their mass transit systems and their passenger cars and locomotives.
   In North America all the trains of the Montreal Metro are equipped with
   it, as are new light rail systems in Denver, Baltimore and New Jersey.
   It is also used on light rail vehicles in Minneapolis, the Vancouver
   Skytrain, and the Scarborough RT in Toronto.

Dual couplings and match wagons

   If a wagon with one coupling system needs to be coupled to wagons with
   another coupling type there are four solutions. This may be needed when
   taking metro rolling stock from its manufacturer to the city where it
   is to be used:
     * hope that dual fitment of the couplings is possible.
     * use a match wagon(s) which have different couplings at either end.
     * use a coupling adaptor.
     * for emergency use only, use a rope. Also useful if a coupler is
       damaged or broken off.

   Only some kinds of couplings coexist on the end of a wagon at the same
   time, because amongst other reasons they need to be at the same height.
   For example, in the Australian state of Victoria, engines had the AAR
   (Janney) coupler, with buffers, and the chain mounted on a lug cast
   into the AAR (Janney) coupler.

   A match wagon or match truck (also known as a barrier vehicle / wagon
   in Britain) has different kinds of couplings at each end. If a pair of
   match wagons is used, a rake of wagons using coupling A can be inserted
   into a train otherwise using coupling B.

   A coupling adaptor might couple to an AAR (Janney) coupling on a wagon,
   and present, for example, a meatchopper coupler to the next wagon. Such
   an adaptor might weigh 100 kg.

Sets of carriages

   Automatic couplers like the Janney are safer in a collision because
   they help prevent the carriages telescoping. British Rail therefore
   decided to adopt a Janney variant for its passenger carriages, with the
   coupler able to swing out of the way for coupling to engines with the
   traditional buffer and chain system.

   In New South Wales, sets of carriages were permanently coupled with a
   fixed bar, since the carriages were only ever disconnected at the
   workshops. Freight cars are sometimes coupled in pairs or triplets,
   using bar couplings in between.

   Articulated sets of carriages or wagons share the intermediate bogies,
   and have no need for couplings in the intermediate positions.

Coupler conversion

   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 lots of problems with transitional incompatibilities, or
   overnight, which requires a lot of planning.

Japan

   Japan converted its British-derived buffer and chain couplings to the
   American Janney coupling over a period of a few days in the early
   1920s, after considerable preparation.

Australia

   Australia, with its break of gauge, has always had different couplers
   on different systems, and has generally adopted gradual conversion.

Europe

   While Europe has chosen an automatic coupler compatible with the Soviet
   one, except for some trial installation, no action has been taken to
   implement the conversion, due to cost.

America

   Once Congress passed a law mandating conversion from the link and pin
   coupler to the Janney coupler, railroads in the United States had only
   a few years to implement the change. The railroads in North America
   form one unitary system, and uniformity of couplers is important for
   smooth interchange of rolling stock.

Latin America

   Railways in Central and South America are fragmented by gauge,
   geography, and financial and technical heritage. While some systems
   have adopted the American Janney coupler, others retain the British
   buffer and hook (buffer and chain) coupler (see above).

Soviet Union

   Russia and Central Asia used buffer and chain couplings, albeit with
   possibly wider centres for the buffers, until conversion to automatic
   SA3 couplers in the 1960s and 1970s. See also: Intermat/Willison
   coupler, Animation showing SA3 coupling (site only in Russian)

Middle East

   While the middle east is mostly standard gauge, three different
   couplings appear to be in use (not counting Sharfenberg couplings on
   EMU trains). These are buffer and chain, American and Russian types.
   The proposed UAR standard appears to be the American type.

Africa

   South of the Sahara, American Janney, and chopper couplings (not
   necessarily of compatible types) appear to account for most couplings.
   The preferred UAR standard is again the American Janney coupling.

Brake couplings

   Just as railway couplings allow a train of wagons to be reordered,
   couplings are needed for any continuous braking systems.

   See Brake (railway)

Models

   On model railroads, couplers vary according to scale, and have evolved
   over many years. Early model trains were coupled using various
   hook-and-loop arrangements, which were frequently asymmetrical,
   requiring all cars to be pointing in the same direction. In the larger
   scales, working scale or near-scale models of Janney couplers were
   quite common, but proved impractical in HO and smaller scales.

   For many years, the "X2F" or "Horn-Hook" coupler was quite common in HO
   scale, as it could be produced as a single piece of molded plastic.
   Similarly, for many years, a "lift-hook" coupler developed by Arnold, a
   German manufacturer of N-scale model trains, was commonly used in that
   scale.

   The chief competitor of both these couplers, more popular among serious
   modelers, was the Magne-Matic, a magnetically-released knuckle coupler
   developed by Keith and Dale Edwards, and manufactured by Kadee, a
   company they started. While they closely resemble miniature Janney
   couplers, they are somewhat different mechanically, with the knuckle
   pivoting from the centre of the coupler head, rather than from the
   side. A steel pin, designed to resemble an air brake hose, allows the
   couplers to be released magnetically; the design of the coupler head
   prevents this from happening unless the train is stopped or reversed
   with a mated pair of couplers directly over an uncoupling magnet. Once
   the Kadee patents ran out, a number of other manufacturers began to
   manufacture similar (and compatible) couplers.

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