Passenger Brake the year 1900, a speed of 60 miles per hour with long heavy passenger trains became common. For this condition the brakes then in service were inadequate to ensure the safety required. The energy to be dissipated was also so great that high shoe temperatures were developed which caused the shoes to soften as the stop continued, so that under these new conditions the coefficient of friction between the shoe and the wheel remained constant throughout the en tire stop. This fact made the invention of the triple valve possible. In addition to the auxiliary reservoir the (V) triple valve employs a large storage reservoir, known as the supple mentary. The air in the supplementary reser voir is not used for service applications; but during emergency applications it equalizes with the air in the auxiliary reservoir and the brake cylinder. The high brake cylinder emergency pressure thus realized, and the maintenance of the full brake cylinder pressure throughout the stop (possible because the- coefficient of friction between the shoe and the wheel remains con stant), greatly shortened the emergency stop and hence made it safe to run the train at high speeds. The triple valve has four other important advantages, namely, quick re charge of the auxiliary reservoir after a service application, through the undisturbed air in the supplementary reservoir restoring the pressure in the auxiliary reservoir as fast as the pressure rises in its adjacent section of the brake pipe (up to the pressure at which the supplementary and auxiliary reservoirs equalize, which is very close to the maximum brake pipe pressure carried) ; uniform and quick release, after a service brake application, possible because the air initially delivered into the brake pipe after the brake application need only expand through the brake pipe on account of being relieved by the supplementary reservoir of the first stages of recharging the auxiliary reservoir ; gradua tion of release secured by the supplementary reservoir charging the auxiliary reservoir to a slightly higher pressure than that in the brake pipe, when the recharging of the latter is cut off at the brake valve, so that the higher auxiliary reservoir pressure moves the triple valve pistons outward sufficient to cause the exhaust of brake cylinder air to be cut off ; and a provision for each valve to reduce the pres sure in its adjacent section of the brake pipe a moderate service rate after the respective triple valve piston and slide valve have as sumed service position.
With triple valves, including the cr.)) type, up to this time, however, the following condi tions prevailed: (1) Since the brake pipe pres sure reduces during a service brake application at a faster rate than it is restored during a recharging period, less air may leak past the triple valve piston for a given change in brake pipe pressure in the former case than in the latter. This action, combined with a greater frictional resistance of the triple valve piston and slide valve in service than in release posi tion as sometimes existed, occasionally pre vented a triple valve piston and slide valve, which assumed position upon a slight reduction in brake pipe pressure, from being returned to its release position. Thus a stuck brake resulted. (2) The device which normally tended to maintain the brake pipe pressure (feed valve) when in bad condition, permitted the brake pipe pressure to fluctuate through this range of several pounds. In some cases this fluctuation caused a brake application, which thereupon could not be released, as explained above. (3) The brake cylinder pressure de veloped from any application gradually reduced, due to the brake cylinder air changing in tem perature and leaking past the brake cylinder piston to the atmosphere. (4) The pressure intended for any brake pipe reduction depended on the brake cylinder volume which in turn de pended on a certain fixed predetermined travel of the brake cylinder piston. With poor designs and lack of maintenance of brake rigging, this piston travel varied on the different cars, so that different brake cylinder pressures were obtained on various cars throughout the train for the same brake pipe reduction. This con dition often produced rough stops. In addition even the u12) type of triple valve, while repre senting the highest development in the air brake art up to this time, still afforded possibilities of improvements in the following respects: (1) If the triple valve were used on the same train with triple valves which did not have the graduated release feature (that is, triple valves which did not have supplementary reser voirs to recharge the auxiliary reservoirs to a slightly higher pressure than the brake pipe, when the latter was cut off at the brake valve, so that the higher auxiliary reservoir pressure could force the triple valve piston outward, thereby cutting off the brake cylinder exhaust) a rough stop would be produced when an at tempt was made to apply the brakes fully at the beginning of a stop and then to off)) the brake cylinder pressure. The stop would be rough because the triple valves, with out the graduated release feature, would release their car brakes at once due to the immediate and entire exhaust of the brake cylinder air and thus permit their respective cars to lunge forward, while the other triple valves would release their brakes by steps, and thus tend to hold their cars back. If the supplementary
reservoirs were cut off to eliminate the gradu ated release feature, then their respective triple valves would lose their quick recharge feature and high emergency brake cylinder pressure secured through these reservoirs; (2) The was the first triple valve to develop a higher brake cylinder pressure for emergency than for service brake applications. This higher pres sure was secured from air in the supplemen tary reservoir being introduced into the auxil iary reservoir, and the brake cylinder through the operation of a piston valve actuated by the supplementary reservoir exposed one piston valve face forcing the piston valve in the direction of the brake cylinder pressure on the opposite piston valve face. Due to this arrange ment, the differential pressure after a full service brake application was insufficient to actuate it, even if the triple valve piston as sumed position. In other words, the other valve functions; the emergency func tion was made independent of the service so that an emergency could be made after a service brake application; the depletion of brake pipe pressure to a predetermined low degree pro duced an emergency brake application; and a shorter, quicker emergency stop was secured by quicker transmission of the brake pipe re duction, quicker delivery of air to the brake cylinders and high brake cylinder pressure. To obtain what may be termed gidealli train con trol in a practical way with methods that are fundamentally. safe and sound, the Universal valve with electrical appliances was perfected in 1912 (Fig. 7). This valve possesses substantially all the features of the "PO' equip ment, previously mentioned, except the obtain ing of brake cylinder pressure irrespective of piston travel and maintaining it against leakage (provision is made for the addition of these features, when desired) with the addition of the following: Simultaneous application of every brake throughout the train, electri an emergency brake application could not be developed after a service brake application had well started, even though the necessity for a quick, short stop arose after the service brake application had begun; (3) If the brake pipe pressure gradually depleted to a low degree it would be impossible to obtain an effective brake; (4) a shorter, quicker emergency stop was desirable. The above-enumerated desirable improvements were incorporated in the °Pe' equipment with the No. 3-E control valve, which was brought out in 1909. This device automatically developed a greater slide valve resistance for an application than for a release of the brakes so that whenever a brake was applied it could surely be released; the auxiliary reservoir air equalized into a constant volume chamber, connected to a piston, instead of into a brake cylinder whereby this piston per mitted the same pressure to be developed in the brake cylinder from main reservoir air irre spective of brake cylinder leakage or piston travel; graduated release was separated from tally initiated by the brake valve, resulting in a smooth and quick stop, smooth because each car is braked at the same instant, and quick because the time of transmission of the brake application is eliminated; a more power ful brake than heretofore possible without the danger of rough stops on account of all cars being retarded simultaneously; ability to re charge the brake system while the brakes are held applied by closing the exhausts with a magnet valve; same degree of flexibility of brake control as possible with the straight air brake on even a single car realized by electrical appliances on each car ; elimination of the possi bility of the valve assuming emergency posi tion when not intended by making the service and emergency valve mechanisms separate and distinct; simultaneous application of all brakes throughout the train in case of a break-in-two or rupture of the brake pipe obtained by a pneumatic switch on each car, which, when energized by electrical actuation, causes each valve throughout the train to assume emergency position; and the ability to secure a relatively small rise of brake cylinder pressure per pound of brake pipe reduction when a reapplication is made before the brake cylinder air from previous applications has been entirely ex hausted by automatically placing only a portion of the auxiliary reservoir under the control of the equalizing piston during this period ; ability to cut out any features without interfering with others; ability of assembling valve so as to give the equivalent of any past standard valve; and ability to make one size of valve suitable for all sizes of equipment by using removable choke plugs to govern the flow of air instead ofpermanent restriction in the valve structure.