Whenever it was desired to stop the brake application from developing to its fullest possible magnitude, the engineer, by placing the brake valve in 'clap)) position, interrupted the reduction in brake pipe pressure. The auxiliary reser voir pressure, having been reducing up to this time at the same rate as that of the brake pipe, immediately dropped slightly below the now constant brake pipe pressure, whereupon the triple valve pistons were forced slightly inward, thereby resulting in cutting off further flow of air from the auxiliary reservoirs into the brake cylinders. In releasing the bralce, the brake valve was moved into position where air at full main reservoir pressure was permitted to expand into the brake pipe through a large opening, in order to transmit a quick impulse through the brake pipe. The triple valve pistons were thereby forced to their innermost positions whereupon the auxil iary reservoirs were recharged and the brake cylinder air exhausted, as previously explained After a short period elapsed, the engineer placed the brake valve in (running) position to prevent the system from charging to a pressure higher than permitted by the reducing valve, which is operative in "running)) position and is used to govern the maximum pressure carried in the brake pipe. To produce an emergency brake application, the operator moved the brake valve pipe air to flow to one outlet (the brake valve port) at the extreme end of the brake pipe, and furnishing, in addition, a local outlet on each car, the time to apply all the brakes throughout the train was materially reduced. This decreased the length and improved the into "emergency') position where the brake pipe air was vented to the atmosphere through a large opening. The resultant sudden reduction in brake pipe pressure caused the auxiliary reservoir air to force the triple valve pistons and slide valves into their outermost positions where auxiliary reservoir air was admitted into the brake cylinders rapidly. This operation produced a short, quick stop. While the auto matic brake with the plain triple valve made the air brake safe, and the stops quicker and shorter than with the straight air brake, yet as train lengths and weights increased, the stops smoothness of the emergency stop. In other respects, the quick action automatic triple valve was similar to the triple valve. From the time of this invention, train speeds and weights were gradually increased and the train stops accordingly began to lengthen once more. It was known that this increase could be offset for emergency application by raising the brake pipe pressure, because this, in turn, would cause an increase in brake cylinder emergency pres sure. The greater retarding force thus de veloped would not have been objectionable at high speeds on account of the coefficient of again began to become rough and longer, par ticularly with emergency applications.
This condition led Mr. Westinghouse to in vent the quick action triple valve (Fig. 3) in 1::7, which, in assuming "emergency" position, locally reduced the brake pipe pressure. By thus avoiding the necessity for all the brake friction between the shoe and the wheel being low, but as the velocity of the train decreased the accompanying increase in the coefficient of friction would have caused the wheels to slide. Mr. Westinghouse overcame this difficulty in 1894 by inventing the high-speed reducing valve (Fig. 4), which was connected direct to the brake cylinder. This valve permitted the use of high brake cylinder emergency pressure, which it gradually reduced throughout the stop to compensate for the increase in the coeffi cient of friction between the shoe and the wheel. The high-speed reducing valve did not operate for brake cylinder pressures supposed to be developed for service brake applications. Up to, and shortly after, 1900 substantially the same type of equipment was employed for all different classes of steam and electric railway service; but about this time the characteristics of these different classes became so distinctive that it became necessary to develop specific types of air brake appliances for each.
portation during the years mentioned. These inventions are described in sequence of their development as follows: Locomotive Brake Equipment.— In the earlier days of railroading, no brakes were in stalled on the locomotive; then straight air brakes were applied to the engine; next straight air brakes to both engine and tender; and finally, as all the braking force possible had to be developed within a safe limit of wheel sliding, quick action instead of plain brakes were placed on the tender. The necessity of braking the engine as part of the train, under some conditions, and independently, as in switching, grade work, etc., under other con P A classification of air brake equipment with reference to service requirements resulted as follows: (1) Locomotive brake equipment; (2) Passenger brake equipment; (3) Freight brake equipment; (4) Electric traction brake equipment. In each of the above classifica tions quite a number of epoch-making inven tions were brought out between the years 1900 and 1918 by Mr. Walter V. Turner, an eminent American engineer and inventor, which form the basis of rapid developments and improve ments in the art, thereby not only advancing the status of the air brake, but contributing largely to the marked progress in railroad trans •Ig• S ditions, and of avoiding the difficulties ex perienced from variations in braking ratio, due to non-uniformity of piston travel and loss of brake cylinder air through leakage from the locomotive brake cylinder (which unfortunately often had to be located near the hot boiler) re sulted in the development of the No. 6-ET
equipment (Fig. 5) during the period from 1903 to which overcame all these objections.
Freight Brake Equipment—When freight trains were composed of less than 50 cars, the automatic quick action type of triple valve in vented in 1887 fully met the braking require ments. With the later practice of operating 60 and 80 cars per train, however, it was found that, during a service brake application, the brake pipe pressure reduced so slowly toward the rear of the train that the auxiliary reservoir air would leak past some of the triple valve pistons without actuating them and would thus cause a brake failure; that, during a release and recharging operation, the auxiliary reservoirs on the front cars would absorb so much of the air delivered to the brake pipe that the small quantity which reached the rear end of the train would leak past some of the triple valve pistons without forcing them to "release" position so that "stuck" brakes would result; and further, that, if the rear brakes did release, it would be so long after the front ones did so, that in the case of a slow-down, produced by an appli cation and release of the brakes, the front cars all the auxiliary reservoirs throughout the train were ensured; and by automatically restricting the release passage at the head end of the train in order to compensate for the time interval required to start the release of the rear brakes, so that all the brakes tended to release uni formly. To maintain the speed of a given train constant on a given grade requires a certain braking force for every pound weight of the train. This exact braking force cannot be ob tained by merely making one brake application, for two reasons:— First, because it would be almost impossible to reduce the brake pipe pressure the exact amount required; and second, if this were possible, the brake cylinder pressure obtained would soon be lost due to leakage, etc. Consequently, the method employed in practice to secure the proper train control was would violently run out from the rear. During the period from 1903 to 1905, there was also developed the triple valve, which elim inated the objections developed by the increas ingly severe freight brake requirements. The differed from the former type of quick action triple valve by quickly and positively transmitting a service brake pipe reduction by locally reducing the brake pipe pressure in its adjacent section of the brake pipe at a moder ate service rate as soon as it assumed position; by automatically restricting the com munication between the brake pipe and auxiliary reservoir on the front cars during the release and recharging period and thereby enabling far more air to be transmitted toward the rear of the train than heretofore, so thus the releasing of the rear brakes and a uniform recharge of to make a brake application to reduce the train speed; to release the brake cylinder air on each car through a restricted (retaining valve( port (until the retaining valve cut off the exhaust after the brake cylinder air had reduced to a predetermined pressure), while the brake system, in the meantime, was being recharged and the train speed increased; to make another brake application followed by a release; and to continue to repeat this cycle as long as the train was on the grade. Such operation neces sitated that the train be sufficiently short to enable the brake system to be recharged in time to obtain another effective brake application before the train speed developed to an uncon trollable degree; and that the maximum speed reached through the braking cycle be suffi ciently slow to ensure that the train could be stopped at any time. Furthermore, the braking force available on the loaded cars alone was inadequate to control the train speed on some grades of ordinary steepness, so that the prac tice of distributing empty cars throughout the train had to be resorted to, in order to secure the greater force per pound weight provided by the empty cars. As a result, trains on grades were short, only partially loaded and operated at slow speeds. Consequently, in various sec tions, grades restricted, and in fact limited, the traffic. To obviate this condition, the freight empty and load brake was devised, which provides substantially the same per cent retarding force for a loaded as an empty car and requires less air to produce a given brak ing force (the train considered, at least, partially loaded) than heretofore. This invention, there fore, made train stops smooth and greatly im proved grade traffic by permitting higher speeds, longer trains and loading to car capacity. The recent introduction of heavy high capacity freight cars in service (weighing 70,000 pounds empty and 315,000 pounds loaded) required so much air per car, even with the empty and load brakes, that another type of an empty and load brake (Fig. 6) still more economical in air consumption and especially adaptable to these cars was developed.