Page:Encyclopædia Britannica, Ninth Edition, v. 20.djvu/267

RAIL WAY 249 remarkably well, it became evident that for the worst types of acci- dents something more was wanted. The brake as first produced was non-automatic, being worked from the engine only, not by the guard. And, since the power had to travel from the engine along the whole length of the train, there was a loss of valuable seconds of time whilst the brake-blocks were being applied. Mr Westing- house therefore designed a system by which each vehicle was supplied with a complete brake apparatus, carrying its own store of power in the form of an auxiliary reservoir of compressed air, in addition to the brake cylinder already there. By the action of the "triple valve " a later introduction which is fitted to each smaller re- servoir on the branch by which it is connected to the main or brake- pipe, the brakes can be instantly applied. A store of compressed air is maintained throughout the train in the continuous pipe and auxiliary reservoirs ; and so long as the pressure in these is main- tained the brakes are kept off. By a reduction of the pressure in the pipe the triple valve is brought into action, and the com- pressed air in the reservoir flows into the brake - cylinder and applies the brake. The brake can be at once released by restoring the pressure in the brake -pipe, when the compressed air in the cylinder escapes into the atmosphere. In the event of a train being parted and the brake-pipe severed, the escape of air reduces the pressure in the pipe, and the brakes are instantly self-applied. They have thus become known as "automatic" brakes. The com- pressed air by the agency of which the Westinghouse automatic FIG. 44. E, the brake- pipe, extends the whole length of the train, connected between the vehicles by a coupling E', with flexible pipes e', e ; F, the triple valve at the end of the reservoir G ; H, the brake-cylinder, with pistons and rods connected with the brake-levers and the blocks suspended on frames ; h, a branch pipe from the brake-pipe or main to the triple valve and reservoir ; h', a branch pipe from the reservoir and triple valve to the brake-cylinder. brake is worked is stored in a main reservoir on the engine, as well as in the local reservoirs under the carriages, at a pressure of from 70 to 80 lb per square inch. The air is compressed by means of a steam-pump attached to the engine and worked by steam from the boiler. The compressed air is supplied through the brake-pipe, which passes through the whole length of the train to the second- ary reservoirs. A brake-cylinder is fixed near each secondary re- servoir, and the charge enters the cylinder at the middle of its length between the pistons, which are driven apart, one towards each end of the cylinder, and act, through piston-rods and levers, upon the brake-blocks which are applied to the wheels. The pistons are maintained in their central positions in the brake-cylinder, when out of action, by spiral springs which abut on the ends of the cylinders ; and so the brake - blocks are kept clear of the wheels. The general arrangement of the brake-apparatus applied to a car- riage is shown in fig. 44; and the reservoir and brake -cylinder, witn their connexions to each other and to the main pipe, and the intermediary triple valve in section, are shown on a larger scale in fig. 45. The triple valve, by means of which instant automatic ac- tion throughout the train is produced, consists of a piston in a short cylinder, carrying a slide valve, the piston and the valve moving together. A vehicle out of order can be cut out of the system by turning a tap, and brakes which have been applied by the parting of a train can be released by opening a valve on the cylinder. In 1874 a royal commission on railway accidents was appointed, and in June 1875 brake trials were made at Newark. On a level road a train, weighing 208'6 tons, running at a speed of 51 J miles per hour, and fitted with the Westinghouse automatic pressure- brake there tested for the first time on an English railway was brought to a stand in a distance of 825 feet in the course of 18 seconds, the equivalent distance for an initial speed of 50 miles per hour being 777 feet. In trials on the North-Eastern Railway Fig. 45. in July 1879, a train, fitted with the Westinghouse brake, weighing 208 tons, and running at a speed of 51 miles per hour, was stopped in a distance of 621 feet in 14f seconds, the equivalent distance for a speed of 50 miles per hour being 594 feet. In August 1877 the Board of Trade urged the railway companies to united and harmonious action, and stated the requirements which in their opinion were essential in a good continuous brake : it should be efficient in stopping trains ; instantaneous in action and easily applied by engine-drivers or guards ; in case of accident instant- aneously self-acting ; capable of being put on or taken off with facility, on the engine, tender, and eveiy vehicle of a train ; regu- larly used in daily working ; and the materials employed easily maintained and kept in order. That a brake should be instant- aneous in action is evident on considering that at a speed of 50 miles per hour a train advances through 73 feet in a second of time. A striking example of the value of seconds under such cir- cumstances is quoted in the Report, contrasting the working of the Westinghouse compressed-air brake and the Westinghouse vacuum- brake. The rates of speed were nearly the same, about 52 miles per hour, or 76 feet per second. The train with the former brake ran 825 feet, whilst that with the latter ran 1533 feet. Now, it took 7J seconds to put on the vacuum-brakes and 1J seconds to put on the pressure-brakes. The difference, 6 seconds, at 76 feet per second, makes a space of 475 feet traversed by the train before the brake came into action. In consequence of these steps taken * by the Board of Trade all the large railway companies have now (1885) adopted continuous brakes, though some of these do not comply with the conditions of the Board of Trade. The principal question is not now that of automatic versus non -automatic, but of automatic pressure-brakes versus automatic vacuum-brakes. In the latter, as the name indicates, the work is done by the atmo- spheric pressure against the pressure of a comparative vacuum. At 31st December 1878 only 21 per cent, of the total carnage stock was fitted with brakes of some form, of which 12 '8 per cent, were auto- matic ; whilst at 30th June 1884 of the total carriage stock 76 per cent, was fitted with continuous brakes, of which 58 per cent, were automatic.- It appears that there are in the United Kingdom considerably more Westinghouse automatic brakes in operation than any other single system. The same brake is veiy largely, used in America and on the Continent, and at the end of 1884 it had been adopted to the extent of upwards of 15,000 sets for locomotives and 78,000 for carriages. ELECTRICITY. The employment of electricity in the working of railways has Signal- already been referred to in the application of block-signalling to ling, the direction of the traffic, in the working of junctions, the protec- tion of stations and sidings, and the repetition of signals. The first attempt to apply electric power for propulsion on rail- Propul- ways was made by Mr R. Davidson, who in September 1842 tried sion. on the Edinburgh and Glasgow Railway an electro-magnetic loco- motive, running on four wheels and weighing 5 tons. A speed of 4 miles per hour was attained. Electric power was applied in 1881 by Messrs Siemens and Halske of Berlin on an electric railway, the Lichterfelde line, near Berlin ; and since then they have con- structed an electric line 1^- miles long, from Charlottenburg to the Spandauer Bock, and a short line in Costverloren Park near Am- sterdam. They also applied the system to a railway in the mines at Zankerode in Saxony. At the International Electric Exhibition in Paris (1881) an electric line was worked by Messrs Siemens Brothers which carried an average of over 13,000 passengers per week ; and in September 1883 a railway of 3 feet gauge, 6 miles in length, was opened between Portrush and Bushmills in the XX. 32