Buffer (rail transport)

A buffer is a part of the buffers-and-chain coupling system used on the railway systems of many countries, among them most of those in Europe, for attaching railway vehicles to one another. Fitted at the ends of the vehicle frames on the buffer beam, one at each corner, the buffers are projecting, shock-absorbing pads which, when vehicles are coupled, are brought into contact with those on the next vehicle. The buffer itself comprises the buffer plates which take the impact. The draw chain used between each pair of vehicles includes a screw which is tightened after coupling to shorten the chain and keep the buffers pressed together. Such is known as a 'screw coupling'. Historically, coupling chains were no more than that, a short length of heavy chain (typically three links long) with no adjustment. These would result in a 'loose-coupled train' in which the buffers of adjacent vehicles would only touch when the coupling chain was fully slack, such as when being pushed or going down hill. The buffers in the very earliest days of railways were rigid dumb buffers made of wooden blocks with a metal cap at the end. For example, Germany's first commercially successful locomotive, the Adler, built in 1835, had wooden buffers. In the 1830s the first spring-loaded buffers were introduced on the Liverpool & Manchester Railway and during the mid-19th century sprung buffers were fitted to all coaches and wagons. The original English buffer plates were the same on each side, so that there was an occasional tendency for them to slide off each other and become locked. German railway buffer plates are flat on one side and convex on the other to reduce this tendency to slide off. The rod buffer was the earliest German type of sprung buffer. The first ones consisted of a steel rod that carried the buffer plate at one end. The buffer rod pushed backwards on a spiral volute spring (coil spring), which was supported by a strong sheet metal cylindrical sleeve. Compressing the spring absorbed the impact.