Air brake

“ If a train parts, or if the air leaks out of the train-pipe, the brakes go on. This automatic principle is a vital one in most safety appliances, and it is secured in the case of the air-brake by one of the most ingenious little devices that man ever contrived, that is, the triple valve, which is placed in the piping system between the brake-cylinder and the car-reservoir. This triple valve has passages to the brake-cylinder, to the car-reservoir, to the train-pipe, and to the atmosphere. ”

“ When the size and speed of the car increases, however, these hand-brakes do not give sufficient control, and power brakes have to be adopted. Of these there are several forms that have proved successful in practice. The one most extensively used in electric railways is the air-brake, which is similar in its mechanical operation to the air-brake used on steam railways. The compressed air required for the operation of the brake is obtained by means of an air-pump driven by an electric motor, the circuit of which is controlled by a switch actuated by the pressure of the air in the receiving tank. ”

“ While the automatic brake had thus obviated the most important defects of the old or straight air brake, and came into general use upon passenger trains throughout the country, it was found, in practice, upon long freight trains, that the air from the auxiliary reservoirs did not act with sufficient promptness upon the brakes of the rear cars, whee a particularly speedy action was required, and that it would be necessary to devise some other means for cases of special emergency. ”

“ The Westinghouse air brake (Fig. 50) uses air at a pressure of about 70 lbs. to the square inch. The essential parts as shown are a reservoir R, the brake cylinder C and a triple valve V, placed under each car with an air pipe P, leading to the engine. This is connected to R by the triple valve V. When the pressure in P is reduced by the engineer or by accident, the triple valve operates so as to admit air from R into the cylinder C pushing the piston H to the left. H is connected to the brakes by levers which press the brake shoes strongly against the wheels. ”

“ A. The air brakes should be released and a sufficient number of hand brakes applied to hold the [Pg 242] train. Never rely on the air brake to hold the train for any length of time.
200. Q. Why is it dangerous to repeatedly apply and release the brakes without giving time for the auxiliaries to fully recharge?
A. As time is required to charge the auxiliaries, the feed groove in the triple valve being small, if the brakes are repeatedly applied and released without giving time to recharge, the braking power will be lost. ”

“ Again, if the air-pressure in the brake-cylinders is so high, and the adjustment of the levers such that an instant application of the full pressure will stop the rotation of the wheels, and cause them to slide on the rails, the stop will take longer than if the wheels continued to revolve. The maximum [199] braking effect is obtained when the pressure on the wheels is as great as it can be without causing them to slide, and it may happen that a quicker stop can be made by putting the engineer's valve to the service-stop position than by trying to make an emergency-stop. ”

“ When the handle E is turned so as to prevent the clappet D from rising, the rapid action is cut out and the brake acts as an ordinary vacuum automatic brake. A modification of the device for obtaining accelerated action, described above in connexion with the Westinghouse brake, is also applicable. Accelerating chambers, again containing air at atmospheric pressure, are provided on each vehicle and are connected with the train-pipe by valves which open as the vacuum in the latter begins to decrease with the operation of the driver’s valve. ”

“ In an American brake lately exhibited on a long freight train, a smaller electro-magnet is used, but the same end is accomplished by multiplying the power by the intervention of a lever and wheel. The other type of so-called electric brake is that in which [195] the motive power is compressed air, and the function of the electric device is simply to manipulate the valves under each car, by which the air is let into the brake-cylinder or allowed to escape, thus putting on or releasing the brakes. ”

“ With steam or air power, the brake would be applied with its full force almost instantaneously, thus subjecting the various parts of the mechanism to very severe and objectionable strains, unless the valves were modified so as to regulate the admission of the steam or air. ”

“ Thanks to automatic air brakes, the life of a passenger brakeman is now a very easy one as compared [Pg 136] with the same life a few years ago. The brakeman of those days, almost as greasy and smoke begrimed as a fireman, spent most of his time on the swaying platforms between cars amid showers of cinders and clouds of blinding dust. ”

“ Every car carries at least two brakes of band pattern—one, usually worked by a side hand-lever, acting on the axle or hubs of the driving-wheel; the other, operated by the foot, acting on the transmission gear (see Fig. 48) . The latter brake is generally arranged to withdraw the clutch simultaneously. Tests have proved that even heavy cars can be pulled up in astonishingly short distances, considering their rate of travel. ”

“ Don’t, then, subject your bearings to an unnecessary strain by forcing your motor to labor as it must, if too steep a hill is taken on too high a gear. See that your hand brake can lock your wheels. On a five-mile grade one brake may burn out, and on most cars in this country the hand brake is next to worthless from lack of use and care. Letting the engine act as a brake is a good practice on long descents.
On going through sand or mud that looks as if it might stop you, change into a lower gear and don’t lose your forward momentum. It is easier to keep a car going than to start it again. ”

“ As every car is equipped with two distinct sets of brakes, drivers should learn to use first one and then the other on long grades, and this may be helped out considerably by using the motor as a brake—that is, by cutting off the ignition and allowing the machine to push the engine under compression, and even more by engaging a lower gear before cutting off the ignition, so that there is a greater leverage obtained to retard the car. ”

“ It then becomes impossible for a driver to run his train in ignorance of any defect in his brake apparatus because such defect at once discloses itself by applying the brakes and stopping the train. Thirdly, that each vehicle shall carry its own brake power in such a manner that the destruction of the brake apparatus on one or more of the carriages shall not affect the efficiency of the brakes upon any of the others. No continuous brake which does not comply with such conditions can ever be satisfactory.--The Engineer. ”

“ Caution.—After you have set the gears for starting, and before you release the clutch pedal, always reach and make sure that the emergency brake lever is in the neutral position. New drivers invariably forget to do this, which results in severe strain on the bearings, and causes them to get loose; the average brake band will not stand more than fifteen to twenty minutes of continuous contact before it burns or wears beyond the point of usefulness. ”

“ The simplest way of applying a brake is by muscular force, exerted through a hand or foot lever or through a screw, by which the brake block is pressed against the rim of the wheel or the band brake tightened on its drum. This method is sufficient in the case of most road vehicles, and is largely used on railway vehicles. But the power thus available is limited, and becomes inadequate for heavy vehicles moving at high speeds. ”

“ Non-automatic brakes can be applied only by the person (usually the engine-driver) to whom the management of them is given; they may become inoperative on all the coaches, and always on those which have become detached, if a coupling or other important and generally essential part is broken. Many mechanical and several hydraulic and electrical continuous brakes have been invented and tried; but experience has shown them so inadequate in practice that they have all practically disappeared, leaving the field to the air and the vacuum brakes. ”

“ Perhaps the most serious danger in the car mechanism is the brake. Mr. Harold F. Blanchard writing in Motor (New York) , argues that more than half, probably as much as 90 per cent of all motor accidents may be eliminated by making the stopping ability of motor vehicles a maximum instead of 25 to 50 per cent, as is now the rule. He would have brakes put on all four wheels and claims thereby the braking power of the machine can be more than doubled. ”

“ The brake is of course of a totally different kind from that in ordinary use, which would be of no service whatever on such inclines, as the wheels, even if the brake were so powerful as to stop their revolution, would slide down the hill by the mere force of gravity. Here, however, the brake consists in an ingenious adaptation of the means which are employed in driving the engine. ”

“ Band brakes are usually lined with leather, to increase the friction between the band and the drum, and this often gives rise to troubles in the burning of the leather when the brake is applied for a considerable period, as in the descent of a long hill. The emergency brake has advantages in that it operates through the friction of metal against metal, but excessive heat from continued application may be enough to melt the metal and fuse together the shoe and drum. ”

“ The ignition may be switched off or on as the occasion requires. Switching it off gives greater braking power. The clutch must be left engaged, and the brakes may be used to help. It is well to use first one brake and then the other in descending long grades, as too long an application of one will cause it to heat and burn the friction material. ”

“ Every motor vehicle other than a motorcycle shall have brakes which can be easily operated by the driver when in his driving position. These brakes shall be capable of performing the following three braking functions:
(a)
A service brake capable of slowing down the vehicle and of stopping it safely, rapidly and effectively, whatever its conditions of loading and whatever the upward or downward gradient of the road on which it is moving ”

“ In this statement we find a list of accidents which have been avoided by the use of the brake, and these accidents are classified under different heads, such as Collisions, Obstacles on the Line, Rolling-stock not removed in time, and so forth. Upwards of forty disasters have been clearly avoided by the prompt use of the brake. On the other hand, the brake itself will sometimes get out of order and refuse to act at the critical moment. ”

“ When a locomotive engineer is braking a mixed-consist [3] passenger train, according to Amtrak airbrake instructions for the power braking method, he should reduce throttle to not greater than run 4 position and then make an initial automatic airbrake reduction. Next, he should release the locomotive independent brakes and reduce throttle to no greater than run 2 position, he should not increase the throttle above that position until brake release has been initiated. The locomotive engineer should make additional reductions with the automatic airbrakes, as needed, to slow or stop. ”

“ The breeching is, or ought to be, considered indispensable in a hilly country, even with light vehicles, and is a proper precaution in all cases where women or children act as coachman.
Brakes are a French invention, and might be supposed to come under much the same strictures as the breeching. But while a breeching is useful and never out of place, except perhaps on the leaders where horses are driven in front of each other, the brake is so often misused, with consequent damage to the horse, the harness, the vehicle, and the skill of the driver, that it almost deserves a chapter by itself. ”

“ The approach of the corves toward the pit mouth was signaled by a bell, brought into action by a piece of mechanism worked from the shaft of the engine. When the bell sounded, the brakesman checked the speed by taking hold of the hand-gear connected [118] with the steam-valves, which were so arranged that by their means he could regulate the speed of the engine, and stop or set it in motion when required. Connected with the fly-wheel was a powerful wooden brake, acting by pressure against its rim, something like the brake of a railway carriage against its wheels. ”

“ He further maintains that the braking power of the ordinary car is extremely low, due, sometimes to the design of the braking system and sometimes to the failure of the owner to adjust the brakes properly. He states that a car equipped with an efficiently constructed system of brakes on four wheels may be stopped from a speed of 30 miles per hour in 36 feet, whereas an average car in the hands of the average motorist will require from 100 to 150 feet. He thinks the brake should be powerful enough to lock the wheel through which it acts. ”

“ We not only had to make the turns, which were just as sharp as on the Austrian side, but it was necessary to watch the straining brakes, releasing them when the grade permitted and alternating the emergency brake with compression. This was a feat demanding all the qualities of motormanship. Coolness and good judgment were indispensable at every curve of the descent. The road turned icy corners and edged along precipitous cliffs. If the brakes had refused to work, it would have been fatal; the downward plunge of the car would have been beyond control in a few seconds. ”