156 TRIPLE VALVES 



This movement of the piston opens a feed-groove in the body 

 bushing and air therefore feeds past piston 5, through the 

 feed-groove into the slide-valve chamber which communicates 

 with the auxiliary reservoir. The air continues to feed past 

 piston 5 as long as brake-pipe pressure is greater than the 

 auxiliary pressure. The usual brake-pipe pressure is 70 lb., 

 and when the auxiliary pressure has reached this amount, 

 the pressures in the chambers above and below the piston are 

 equal and the auxiliary is said to be fully charged. The lower 

 side of piston 5 is generally referred to as the train-pipe side 

 and the upper as the auxiliary side, or the ^tide-valve side. 



Charging Auxiliary Reservoir. A modern triple valve should 

 charge an auxiliary from to up 70 lb. in about 70 sec., with a 

 constant train-pipe pressure of 70 lb. With the triple in release 

 position and the auxiliary charged, there will be 70 lb. in the 

 train pipe, 70 lb. in the auxiliary, and the atmospheric pressure 

 in the brake cylinder, since the slide-valve cavity connects the 

 brake cylinder with the atmosphere. 



OPERATION OF PLAIN TRIPLE VALVES 

 Applying Brakes. To apply brakes, it is necessary that the 

 brake-pipe pressure be reduced below auxiliary pressure; this 

 may be made in the usual way by the engineer, by the use of 

 the conductor's valve, or by a break-in-two, a burst hose, or 

 a heavy leak in the brake pipe. If the engineer makes a reduc- 

 tion of 7 lb. in the brake pipe, only 63 lb. will remain in the 

 chamber below piston 5, whereas at the beginning of the reduc- 

 tion there will be 70 lb. in the chamber above piston 5. The 

 greater auxiliary pressure will force piston 5 downwards; this 

 closes the feed-groove and unseats the graduating valve 7, 

 allowing auxiliary air to enter the slide valve. By the time 

 the graduating valve is unseated and the feed-groove closed, 

 the shoulder on the upper end of the piston stem has engaged 

 the slide valve and begun to move it down. As the slide 

 valve moves down, the exhaust cavity is first closed, preventing 

 the escape of brake-cylinder air. When the knob touches 

 the graduating stem, the piston 5 is prevented from making 

 any further downward movement. With the triple piston 

 in this position, the service port of the slide valve is directly 



