224 



TRIPLE VALVES 



the P triples. This is due to the fact that brake-pipe and 

 auxiliary pressures are practically balanced in the new equip- 

 ment at the time of application so that the triple valve responds 

 at once. With the P triples, the excess brake-pipe pressure 

 had to be drawn off before the triples would respond to the 

 reduction. 



In Fig. 3 are shown the results of rack tests of the old, or 

 high-speed, and new, or LN, equipments, with 110 Ib. brake- 

 pipe pressure, when emergency applications are made. These 

 curves illustrate the high emergency and the retaining features 

 of the LN equipment. This equipment gives a brake-cylinder 

 pressure of 104 Ib. in about 4.5 sec. and maintains it constant 



FIG. 3 



throughout the stop; the old equipment gives a maximum of 

 83 Ib. in about 5 sec., but this pressure gradually decreases to 

 60 Ib. in about 45 sec.; the pressure though is maintained 

 constant thereafter. For the same initial brake-pipe pressure, 

 therefore, the LN equipment gives 21 Ib. higher maximum 

 brake-cylinder pressure, and 32.5 Ib. average pressure for the 

 first 45 sec. After 45 sec., the LN equipment gives 44 Ib. 

 greater brake-cylinder pressure. This greater pressure through- 

 out the stop is provided to compensate for the lowered coef- 

 ficient of friction between the brake shoes and the wheels that 

 results from the increased amount of work required from each 

 brake shoe with the LN equipments. 



