PART XXIII.

CONTINUOUS TRAIN BRAKES.

QUESTION 441. _What are meant by automatic or continuous train brakes?_

_Answer._ Continuous train brakes are brakes which can be applied to all the cars of a train by the locomotive runner on the locomotive. In some cases such brakes are arranged in such a way that they can also be applied from any car in the train, or are made self-acting in case of an accident, such as a car getting off the track or a train breaking in two.

QUESTION 442. _What are the principal systems of brakes of this kind in use?_

_Answer._ What is called, after its inventor, the Westinghouse atmospheric brake is now used more than any other. Next to this, Smith’s vacuum brake is used most. Besides these two, Creamer’s, Ward’s, Loughridge’s and Henderson’s systems of brakes are used to a limited extent. The two first are, however, the only ones which have come into sufficiently extensive use as yet to justify us in describing them here.

QUESTION 443. _How does the Westinghouse brake act and how is it constructed?_

_Answer._ As its name indicates, the medium employed for transmitting the power for operating the brakes is atmospheric air.

[Illustration: Fig. 223. Scale ¹⁄₂ in. = 1 foot.]

This is compressed to any required density by a steam pump which is located between the driving-wheels, or in any other convenient place on the locomotive. This pump is shown in section in fig. 223 and consists of two cylinders, the upper one, _A_, the steam cylinder, the piston of which is connected by its rod with the piston in the lower cylinder, _B_. This latter is operated by the steam piston, and at each stroke a quantity of air, equal to the space swept through by the lower piston, is compressed and thus forced into a cylindrical reservoir, which is usually placed under the foot-board of the locomotive, in which it is stored for use at any time when the brakes are to be applied. The air and steam cylinders are supplied with suitable valves for admitting and releasing the air and steam. From this reservoir it is conducted back under the tender and cars by pipes, which are connected together between the engine and tender and between the cars by India rubber hose. Two pieces of hose are attached to the engine and also to each end of the tender and cars, so that in case one piece should break the others will act. Each of these pieces is united or coupled to the corresponding piece opposite to it by a peculiar coupling made for the purpose, so that they can be quickly disconnected if the cars, engine or tender are uncoupled.

Under the tender and also under each car is a cylinder and piston. The compressed air is conducted to this cylinder in front of the piston when the brakes are to be applied. As the piston-rod is connected by a bell crank to the brake levers when the piston is forced out by the pressure of the air, the brakes are at once applied to the wheels. As the reservoir under the foot-board is connected by the pipes which have been described with the cylinders under each car and the tender, by simply opening communication between the reservoir and the pipes, the air at once rushes from the reservoir back through the whole length of the train, and so rapid is its motion and quick its action that only a second or two intervenes between the opening of communication and the application of the brakes. To relieve or “let off” the brakes it is only necessary to close the reservoir cock and open communication from the air-pipes to the external atmosphere, when the compressed air in the brake cylinders will escape, and the springs ordinarily used on car brakes will cause the pistons to resume their former positions.

For the purpose of opening the connection from the reservoir to the brake cylinder, and closing this connection and opening one from the latter to the external air, a single three-way cock is commonly used. This is arranged at such a point as to be under the control of the engineer, so that he can at pleasure turn on the compressed air with any degree of force, instantaneously, or slowly, or with a varying power, or by another turn of the cock let it off as freely, still keeping it under the same complete control.

[Illustration: Fig. 224. Scale 1¹⁄₂ inch = 1 foot.]

QUESTION 444. _How does the vacuum brake act and how is it constructed?_

_Answer._ The power is applied to the brakes of the cars in this system by exhausting instead of compressing the air. This is done by means of an ejector, of which fig. 224 is a section. This operates somewhat like an injector. Steam is admitted into the pipe _B_, and escapes through the annular or circular opening _a a_. The effect of this is to create what is called an “induced current,” or to draw the air from the pipe _C′ C_, which, with the steam, escapes at _A_. This produces a partial vacuum in the pipe _C_, which extends back under the cars. The pipes under the cars are connected together by rubber hose, which are prevented from collapsing by coils of wire inside. Under the tender and under each car are India rubber cylinders with cast iron ends, one fastened to the car and the other movable. The rubber cylinders can be extended or compressed somewhat like the bellows of an accordeon. The rubber is supported by iron rings inside, placed from 4 to 6 inches apart, so as to prevent them from collapsing when the air is exhausted from them. When this is done the pressure on the movable cast iron end draws it towards the fixed one, and by attaching the former to the brake levers by a rod, the force of the pressure on the head is communicated to the brakes.

The ejector is placed on top of the boiler, and when the brakes are to be applied the locomotive runner opens a valve, which admits steam into the ejector, which instantly begins to produce a partial vacuum and thus apply the brakes. When the pressure of the brakes is to be released, the release valve, _D_, is opened, which admits air into the pipe, _C_, through which it is conducted back to each of the India rubber cylinders, and thus counteracts the pressure on the ends and releases the brakes.

Both the atmospheric and the vacuum brakes have recently been applied to the driving-wheels of locomotives with very excellent results.