Coupling (railway)

A coupling (or a coupler) is a mechanism for connecting in a train. The design of the coupler is standard, and is almost as important as the track gauge, since flexibility and convenience are maximised if all rolling stock can be coupled together.

The equipment that connects the couplings to the rolling stock is known as the draft gear.

The different types of coupling do not always have formal or official names, which makes descriptions of the couplings in use on any railway system problematic.

The standard type of coupling on railways following the British tradition is the buffer and chain coupling used on the pioneering Planet class locomotive of the Liverpool and Manchester Railway of 1830. These couplings followed earlier tramway practice but were made more regular. The vehicles are coupled by hand using a hook and links with a turnbuckle that draws the vehicles together. In Britain, this is called a screw coupling. Vehicles 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. The earliest buffers were fixed extensions of the wagon frames, but later spring buffers were introduced.

This coupling is still the standard in European countries (except the former Soviet Union, where the SA-3 automatic coupler is used).

The link-and-pin coupling was the original style of coupling used on North American railways. After most railroads converted to semi-automatic Janney couplers, the link-and-pin survived on forestry railways. While simple in principle, the system suffered from a lack of standardisation regarding size and height of the links, and the size and height of the pockets.

The link-and-pin coupler consisted of a tube-like body that received an oblong link. During coupling, a rail worker 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 them out of the way of the coupler pockets in time. 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 not use the club, and risked injury.

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Wikipedia