TRIPLE VALVES 161 



a tour through the Middle West and the East. This tour 

 established the quick-action brake as the standard for both 

 freight and passenger service. 



As will be noted, the straight-air brake and the plain triple 

 valve were developed for passenger service, whereas the 

 quick-action triple valve was developed for freight service, 

 although eventually it was adopted as standard for both 

 freight and passenger service, also, the quick-action triple 

 was designed and developed for use on trains of fifty cars 

 or less, the fifty-car train to be the maximum. From the 

 very beginning, the length, weight, and speed of trains have 

 been limited by the capacity of the brake for the safe and 

 efficient control of the train. The hauling power of the 

 locomotive has always been a step or two in advance of the 

 brake control; consequently, when the length of the train 

 was limited to fifty cars by the brake control, the tonnage 

 of the train was increased to the hauling power of the loco- 

 motive by increasing the capacity of the cars. As the capacity 

 of the cars increased, the braking power on the car was neces- 

 sarily increased in proportion, as was also the hauling power 

 of the locomotive. 



The desire to haul trains of more than fifty cars led to the 

 "part-air train" practice, which consisted in using a sufficient 

 number of the head-end brakes to control the train, the rear- 

 car brakes not being used. This practice was quite success- 

 ful, and under it the length of the train gradually increased 

 from fifty to eighty and ninety cars. As fifty or fewer than 

 fifty brakes were in use on such trains, the brake system oper- 

 ated without difficulty and engineers soon learned to control 

 the slack of the non-air cars so as to prevent severe shocks 

 and break-in-twos. 



Next came the rule to increase the percentage of air-braked 

 cars from time to time, until now it is customary to run 

 all-air trains. As sixty- to eighty-car trains have become a 

 fixed practice, and one-hundred-car trains are not uncommon, 

 the air-brake manufacturers have been kept busy experiment- 

 ing and improving their apparatus in the endeavor to keep 

 the brake up to the requirements of the service. To control 

 an all-air train of eighty to one hundred cars by means of the 

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