Buffers and screw

Buffers and chain coupler (also called buffers and screw, screw coupler, or English coupler; in EU standards, it's two devices: buffers and draw gear and screw coupling) is the standard train coupling system used in Europe, outside the former Soviet Union. It is also occasionally used outside Europe.

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 shunting shocks. By contrast, the semi-automatic Janney coupler usually requires comparatively jarring encounters in order to engage the coupling fully. The earliest buffers were fixed extensions of the wagon frames, but later spring buffers were introduced.

Inefficient and slow, the European system is also relatively unsafe because — like the link-and-pin coupling used in North America (and especially the United States) before the end of the 19th century, when the Janney coupler began universally replacing it there — the European system requires manual coupling between vehicles, exposing workers to the risk of being crushed. However, there is no need for the worker to go between vehicles while they are moving, which is an improvement over the original link-and-pin types.

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.

This coupling is still the standard in European countries (except the former Soviet Union, where the SA-3 automatic coupler is used). Coupling is done by a worker who must climb between the cars. First he winds the turnbuckle to the loose position, and then he can hang the chain on the hook. After hanging the chain on the towing hook the turnbuckle handle is stowed on the idle hook to prevent damage to itself, the vehicle, or the brake pipes. Only shunting is permitted with a dangling chain. Disconnected brake pipes must be stowed on dummy connectors, to allow proper operation of the brakes. (The picture shows two coupled cars, with a single brake pipe.)

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