volume of freight is raw material and crude food-stuffs, and the distances are great, a low charge per unit of transportation is more important than any consideration such as quickness of delivery; therefore full car-loads of freight are massed into enormous trains, which run unbroken for distances of perhaps 1000 m. to a seaport or distributing centre.
The weight and speed of goods trains vary enormously according to local conditions, but the following figures, which Weight and speed.refer to traffic on the London & North-Western railway between London and Rugby, may be taken as representative of good English practice. Coal trains, excluding the engine, weigh up to 800 or 900 tons, and travel at from 18 to 22 m. an hour; ordinary goods or merchandise trains, weighing 430 tons, travel at from 25 to 30 m. an hour; and quick merchandise trains with limited loads of goo tons make 35 to 40 m. an hour. In the United States mineral and grain trains, running at perhaps 12 m. an hour, may weigh up to about 4000 tons, and loads of 2000 tons are common. Merchandise trains run faster and carry less. Their speed must obviously depend greatly on topographical conditions. In the great continental basin there are long lines with easy gradients and curves, while in the Allegheny and Rocky Mountains the gradients are stiff, and the curves numerous and of short radius. Such trains, therefore, range in weight from 600 to 1800 tons or even more, and the journey speeds from terminus to terminus, including stops, vary from 15 to 30 m. an hour, the rate of running rising in favourable circumstances to 40 or even 60 m. an hour.
Couplers.—The means by which vehicles are joined together into trains are of two kinds—automatic and non-automatic, the difference between them being that with the former the impact of two vehicles one on the other is sufficient to couple them without any human intervention such as is required with the latter. The common form of non-automatic coupler, used in Great Britain for goods wagons, consists of a chain and hook; the chain hangs loosely from a slot in the draw-bar, which terminates in a hook, and coupling is effected by slipping the chain of one vehicle over the hook of the next. For this operation, or its reverse, a man has to go in between the wagons, unless, as in Great Britain, he is provided with a coupling-stick—that is, a pole having a peculiarly shaped hook at one end by which the chain can be caught and thrown on or off the drawbar hook. This coupling gear is placed centrally between a pair of buffers; formerly these were often left “dead”—that is, consisted of solid prolongations of the frame of the vehicle, but now they are made to work against springs which take up the shocks that occur when the wagons are thrown violently against one another in shunting. In British practice the chains consist of three links, and are of such a length that when fully extended there is a space of a few inches between opposing buffers; this slack facilitates the starting of a heavy train, since the engine is able to start the wagons one by one and the weight of the train is not thrown on it all at once. For passenger trains and occasionally for fast goods trains screw couplings are substituted for the simple chains. In these the central bar which connects the two end links has screw threads cut upon it, and by means of a lever can be turned so as either to shorten the coupling and bring the vehicles together till their buffers are firmly pressed together, or to lengthen it to permit the end link to be lifted off the hook.
Another form of coupler, which used to be universal in the United States, though it has now been almost entirely superseded by the automatic coupler, was the “link and pin,” which differed fundamentally from the couplers commonly used in Europe, in the fact that it was a buffer as well as a coupler, no side buffers being fitted. In it the draw-bar, connected through a spring to the frame of the car, had at its outboard end a socket into which one end of a solid link was inserted and secured by a pin. The essential change from the link and pin to the automatic coupler is in the outboard end or head of the draw-bar. The socket that received the link is replaced by a hook, shown at A in fig. 28, which is usually called the knuckle. This hook swings on the pivot B, and has an arm which extends backwards, practically at right angles with the working face of the hook, in a cavity in the head, and engages with the locking-pin C. This locking-pin is lifted by a suitable lever which extends to one or both sides of the car; lifting it releases the knuckle, which is then free to swing open, disconnecting the two cars. The knuckle stands open until the coupling is pushed against another coupling, when the two hooks turn on their pivots to the position shown in fig. 28, and, the locking-pin dropping into place, the couplers are made fast. This arrangement is only partly automatic, since it often happens that when two cars are brought together to couple the knuckles are closed and must be opened by hand. There are various contrivances by which this may be done by a man standing clear of the cars, but often he must go in between their ends to reach the knuckle.
Fig. 28.—Automatic Coupling for Freight Cars (U.S.A.).
This form of automatic coupler has now gained practically universal acceptance in the United States. To effect this result required many years of discussion and experiment. The Master Car Builders’ Association, a great body of mechanical officers organized especially to being about improvement and uniformity in details of construction and operation, expressed its sense of the importance of “self-coupling” so far back as 1874, but no device of the kind that could be considered useful had then been invented. At that time a member of the Association referred to the disappearance of automatic couplers which had been introduced thirty or forty years before. This body pursued the subject with more or less diligence, and in 1884 laid down the principle that the automatic coupler should be one acting in a vertical plane-that is, the engaging faces should be free to move up and down within a considerable range, in order to provide for the differences in the height of cars. By the fixing of this principle the task of the inventor was considerably simplified. In 1887 a committee reported that the coupler question was the “knottiest mechanical problem that had ever been presented to the railroad,” and over 4000 attempted solutions were on record in the United States Patent Office. The committee had not found one that did not possess grave disadvantages, but concluded that the “principle of contact of the surfaces of vertical surfaces embodied in the Janney coupler afforded the best connexion for cars on curves and tangents”; and in 1887 the Association recommended the adoption of a coupler of the Janney type, which, as developed later, is shown in fig. 28. The method of constructing the working faces of this coupler is shown in fig. 29. The principle was patented, but the company owning the patent undertook to permit its free use by railway companies which were members of the Master Car Builders’ Association, and thus threw open the underlying principle to competition. From that time the numerous patents have had reference merely to details. Many different couplers of the Janney type are patented and made by different firms, but the tendency is to equip new cars with one of only four or five standard makes. The adoption of automatic couplers was stimulated in some degree by laws enacted by the various states and by the United States; and the Safety Appliance Act passed by Congress in 1893 made it unlawful for railways to permit to be hauled on their lines after the 1st of January 1898 any car used for interstate commerce that was not equipped with couplers which coupled automatically by impact, and which could be uncoupled without the necessity for men going in between the ends of the cars. The limit was extended to the 1st of August 1900 by the Interstate Commerce Commission, which was given discretion in the matter.