THE TRIPLE VALVE.
This is the part whose operation gives the brake its automatic action. Those who have opposed this form of brake have made great objection to the complicated nature of the triple valve. But some familiarity with the device shows that it is far from being complex, considering the functions it performs. It is merely a piston-valve carrying a slide-valve along with it.
The arrangement of the parts of the triple valve is shown in [Fig. 34].
Fig. 34.
The triple valve has a piston 5, working in the chamber B, and carrying with it the slide-valve 6. Air enters from the main pipe through the four-way cock 13 into the drain-cup A, and passes to the chamber B, forcing the piston up, and uncovering a small feeding-groove in the upper part of the chamber, which permits air to flow past the piston into the auxiliary reservoir, while, at the same time, there is an open communication from the brake-cylinder to the atmosphere through the passages d, e, f, and g. Air will continue to flow into the auxiliary reservoir until it contains the same pressure as the main brake-pipe.