144 ENGINEER'S BRAKE VALVES 



PC. No. Ref. No. Name of Part 



18.454 6 Piston. 



18.455 7 Supply valve. 

 1,411 8 Supply- valve spring. 



IS, 286 9 Piston spring. 



3,054 10 Piston-spring tip. 



16,183 12 Regulating valve. 



1,060 13 Regulating-valve spring. 



6,509 14 Regulating-valve cap nut. 



1.062 15 Spring box. 



1.064 16 Diaphragm ring. 



1.063 17 Diaphragm, 2 p : eces required, each. 



1.065 18 Diaphragm spindle. 

 1,068 19 Regulating spring. 



11,261 20 Regulating nut. 

 1,067 21 Check-nut. 



Operation of Feed-Valve. At such times as the feed-valve 

 is not under pressure, the supply valve 7 is closed while the 

 regulating valve 12 is open. The regulating spring 19 forces 

 the supply valve 17 back until it covers its port, while the regu- 

 lating spring 19 forces the diaphragm to unseat the regulating 

 valve 12. When the brake pipe is charged to less than 70 lb., 

 both the supply valve and the regulating valve are open and 

 air is feeding through the feed-valve into the brake pipe. 

 Under those conditions, main-reservoir air enters the chamber 

 to the left of piston 6, forcing the piston forwards until the 

 supply valve uncovers its port. The air then flows through the 

 feed valve into the brake pipe, increasing the pressure there. 



While brake-pipe pressure is less than 70 lb., the regulating 

 valve is held off its seat by the regulating spring and there is 

 direct communciation between the chamber on the right of 

 piston 6 and the brake pipe through the regulating valve. 

 The leakage that takes place past the piston 6 therefore passes 

 directly to the brake pipe, so that the chamber to the right of 

 piston 6, and the chamber to the left of diaphragm 17, are 

 maintained at brake-pipe pressure. When 70 lb. is obtained 

 in the brake pipe, the pressure on the diaphragm 1 7 is sufficient 

 to compress the regulating spring enough to allow the regulating 

 valve to close. This cuts off communication between the cham- 

 ber to the right of piston 6 and the brake pipe, and the leakage 

 occurring past piston 6 then quickly charges the chamber to 

 the same pressure as the pressure in the chamber to the left 



