TRIPLE VALVES 169 



EMERGENCY PART OF TRIPLE 



When, in cases of danger, etc., a sudden reduction of brake- 

 pipe pressure is made, the emergency part of the triple valve 

 is called into play; the triple piston 4 moves out quickly, the 

 graduating spring 22 is compressed, and the triple piston trav- 

 els the full length of its stroke. In this position, auxiliary 

 pressure can pass into the brake cylinder. The removed corner 

 of the slide valve has reached a position directly above a 

 port leading to the chamber above the emergency piston, thus 

 allowing axuiliary air to pass down on to the top of the emer- 

 gency piston 8, forcing it downwards. This downward move- 

 ment unseats the emergency valve 10, and allows the air in 

 the chamber above the emergency check 15 to escape. Brake- 

 pipe pressure beneath this check-valve forces the latter from 

 its seat and air from the brake pipe passes up by it through 

 the unseated emergency valve 10, into the brake cylinder. 

 The emergency valve remains unseated until the pressures 

 above and below piston 8 are nearly equalized, when the 

 spring 12 forces the emergency valve to its seat. 



The position of the removed corner q on the slide valve is 

 such that, as the valve moves forwards to emergency position, 

 it connects the port leading to the chamber above the emer- 

 gency piston with auxiliary pressure before the emergency 

 port in the slide-valve port connects with the port leading to 

 the brake cylinder. The emergency valves therefore open first, 

 consequently, brake-pipe air which passes like a flash through 

 the large openings of the emergency valves is admitted in suffi- 

 cient quantity to give a pressure in an 8-in. brake cylinder, 

 with standard piston travel of about 24 i Ib, when check- valve 

 15 closes. Afterwards, auxiliary pressure discharges into, and 

 equalizes with, the brake cylinder; but, as the cylinder already 

 contains about 24$ Ib. pressure, they equalize at about 60 Ib. 

 pressure instead of at 50 Ib., as in a service application. 



The opening through the emergency port of the slide valve 

 is made smaller than the service port, to retard the flow of 

 air somewhat from the auxiliary reservoir to the brake cylinder 

 during an emergency application of the brakes, so as to allow 

 as much air as possible to enter the brake cylinder from the 

 brake pipe, and thus increase the final brake-cylinder pressure. 



