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Railway coupling

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Knuckle couplers in use. Click to enlarge.

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 is maximised if the couplings can work together no matter what order they come in.

Buffers and Chain

File:European coupler on loco.jpg
traditional coupler

The type of coupling established as standard on railways following the British tradition is the Buffer 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.

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 if the main coupling was not fully trusted. 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.

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 buffer-locked 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 be unsuitable.

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.

The link and pin coupler ultimately proved unsatisfactory because:

  • it made a loose connection between the cars with too much give and play
  • there was no standard design and train crews often spent hours trying to match pins and links while coupling cars
  • links and pins were frequently lost, resulting in substantial replacement costs
  • crew members had to go between moving cars during coupling and were frequently injured and sometimes killed.

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

Meatchopper

Meatchopper couplings consist of a central buffer with a mechanical hook that drops into a slot in that 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.

Meatchopper couplings are not particularly strong, and are supplemented by auxilliary chains.

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

There are a number of automatic train couplings, most of which are mutually incompatible.

Janney coupler

The knuckle coupler (or Janney coupler) was invented by Eli Janney, who received a U.S. patent in 1873 (number 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.

Variations on the Janney coupler have been devised to provide extra protection to cars routinely carrying sensitive or hazardous loads, in case of train wrecks. These variations, generally involving "shelves" or extended knuckles, remain fully compatible with standard Janney couplers, but tend to keep derailments and collisions from uncoupling the cars (thereby preventing the couplers from piercing the ends of the cars).

Trains fitted with Janney couplers can have heavier loads than any other type of coupler. Thus the heaviest coal trains in New Zealand have Janney 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 (1.6km) long, whereas this is unknown in Europe, where most freight trains still use the buffers and chain system.

When the Janney coupling was chosen to be the American standard, there were an amazing 8000 patented alternatives to choose between!

Brake couplings

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

See Brake (railway)

Diesel locomotives

Diesel locomotives come in three kinds:

  • those that cannot operate in multiple unit.
  • those that can operate in multiple unit with locomotives of the same kind.
  • those that can operate in multiple unit with most other locomotives.

Multiple-unit operation is more than standardising the cables that plug together between engines. It also means making the controls and characteristics of the locomotives compatible.

Most American locomotives use the so-called "Association of American Railroad" standard for multiple-unit control.

Control coupling

As trains have become more complicated, with electical power and controls connecting one vehicle to another, systems for coupling these power and control circuits have been needed.

new automatic coupler

Mass transit systems worldwide mostly use specialized couplers that also make electrical connections between cars, such as the Scharfenberg coupler or Scharfenbergkupplung or "Schaku", which has gradually spread from transit trains in Europe to regular European passenger service trains. The Schaku coupler is superior to the Janney Coupler because it makes the electrical and also the pneumatic connections and disconnections automatically. 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.

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.

Older US transit operators use non-Janney electro-pneumatic coupler designs that have been in service for decades.

Models

Model trains are fitted with a wide variety of often mutually incompatible couplings, including:

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 center 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; while Kadee (and its spin-off, Micro-Trains) is still very much in the coupler business, the resulting abundance of cheap Kadee-compatible couplers doomed the horn-hook to obscurity, just as Kadee's decision, in the 1970s, to manufacture N-scale rolling stock had doomed the Arnold coupler.

Sources

See Also

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