406 



TRAIN AIR-SIGNALING SYSTEM 



valve also; but, since the stem makes a rather snug fit, the 

 pressure in chamber A above the diaphragm reduces faster 

 than the pressure in chamber B\ consequently, the diaphragm 

 is forced upwards, and raises the stem, thus opening the port 

 in valve seat 7. The stem is lifted until the groove / is above 

 the bushing, when the air in chamber B escapes quickly through 

 the groove /, the milled spaces in the stem, and the passage e, 

 out to the whistle, causing the latter to give a blast. Air also 

 escapes from chamber A to the whistle, through the passages 

 cc and e, but is restricted in its passage from the train signal pipe 

 into A by the small port d. 



The same reduction of pressure that operates the signal 

 valve also opens the reducing valve, allowing air from main 

 reservoir to flow into, and raise the pressure in, the signal pipe. 

 This increase of pressure, following the closing of the car dis- 

 charge valve, and immediately after the reduction in signal 

 valve, increases the pressure in chamber A faster than in cham- 

 ber B, thus forcing the diaphragm downwards, closing the valve 

 leading to passage e, and stopping the blast of the whistle. 



CAR DISCHARGE VALVE 



The car discharge valve, the construction of which is shown 

 in the accompanying cross-section, weighs 2| Ib. The piece 



~ PIPE TO SIGNAL PIPE 



and reference numbers of the valve and its parts are given in 

 the accompanying list. 



