BUFFER, a member which receives and absorbs the shock of an impact gently, and thus protects other parts from damage. A buffer must contain some flexible material, such as a steel spring, a rubber block, air-cushioning or a hydraulic cylinder. Buffers are employed in railway trains to protect the individual trucks and carriages, as well as the engine and tender.
British Practice.—Buffers are placed at the corners of the car body, and consist of circular or oval heads having long stems extending into the body, as shown by the details of a Great West ern Railway steel carriage underframe designed by C. B. Collett. The volute springs surrounding the stems are gin. diameter over the largest coil, and thrust against steel knees. A stroke of Sin.
is allowed for. An elliptical shape, i sin. by I 9in., is chosen for the buffer faces in order to avoid any possibility of the buffers locking at sharp curves. Buffers for shunting engines have an ex tra large head. Close-coupled vehicles for suburban traffic are sometimes constructed without the two side buffers, there being a central elliptical block, and the draw-bar pulling against rubber springs. In the automatic buffer couplers the coupling end passes through a large-faced buffer, which is sometimes widened to carry two stems fitted with a compensating beam.
The fixed buffer-stop at a terminus, or at the end of a siding, may be a plain wooden beam, though it is often provided with springs. As a safeguard against the partial failure of brakes, the Ransomes and Rapier hydraulic buffer-stops are installed at many important termini. The buffer head carries a long rod that terminates in a piston working in a cylinder filled with water or oil. Passages lead out of the cylinder, permitting the fluid to escape gradually; these are larger at the front end than the back. As the speed is checked, less and less passage is provided, offering a resistance which retards the train without shock or recoil. The lengths of stroke range from 5–I i f t. ; the buffers in the latter case are capable of stopping a train of about 90o tons moving at I om. an hour. (F. H.) American Practice.—The buffer is used in passenger-train cars in combination with the draft gear, and consists of a steel plate carried by three horizontal stems extending into the car body just below the floor level and above the "draw-bar." The plate comes in contact with a similar plate on the adjoining car. The stems which carry the buffer plate carry long coiled springs, the central stem in some designs also acting upon sliding friction members in combination with steel springs. A passenger car buffer serves not only to absorb the impact caused by the collision of two cars, but to take up the slack in the couplers when cars are in a train, and to close up the gap between cars, making it safe for passengers to walk from car to car. Standard practice allows for a total stroke of 51 inches. When cars are in a normal coupled condition, the buffers are compressed 3in., leaving 2 tin. for the absorption of compressive shocks. In freight yards and sidings, a stopping device that slides along the rail is frequently employed. This depends on the friction generated between the rail and a cast-steel shoe upon which the car wheel mounts. As the shoe slides along the rail, the energy of the car is dissipated. Blocks bolted to the end of the rails finally bring the car to rest. (See also RAILWAYS.) Spring buffers also called "bumpers" are fitted to motor-cars to protect the ends from the effects of collision. (X.)