404 TRAIN AIR-SIGNALING SYSTEM 



PC. No. Ref. No. Name of Part 



2.376 9 Piston nut. 



2.378 10 Piston rod. 



2.379 11 Large diaphragm. 



2.380 11 Small diaphragm. 



2.381 12 Diaphragm ring. 

 2,036 13 Regulating spring. 



2.382 14 Regulating nut. 



2.383 15 Check-nut. 



2.367 16 Cock cap. 

 2,231 17 Cock spring. 



2.384 18 f-in union nut. 



2.385 19 |-in union swivel. 



2.386 20 |-in union gasket. 

 2,366 21 Cock key. 



2.368 22 Choke plug. 



2.377 23 Cotter. 



The choke plug 22 restricts the flow of air through the valve 

 so that the reducing valve cannot supply air to the signal pipe 

 faster than the car discharge valve can reduce the pressure. 

 The tension of the regulating spring 13 is adjusted to just with- 

 stand a pressure of 40 Ib. per sq. in. in the chamber above 

 the piston 7. When the pressure is less than this amount, the 

 spring 13 forces piston 7 upwards and the piston stem unseats 

 the supply valve 4- Main-reservoir air is then free to pass 

 through the choke plug 22, supply valve 4, thence to the signal 

 pipe. As soon as the pressure in the signal pipe and chamber 

 above piston 7 reaches 40 Ib., piston 7 is forced downwards and 

 the supply- valve spring 6 forces the supply valve to its seat, 

 closing communication between the main reservoir and the 

 signal pipe. Any reduction in signal-pipe pressure will allow 

 the regulating spring 13 to force piston 7 upwards, thus opening 

 the supply valve again. The valve then remains open until the 

 signal-pipe pressure is again raised to 40 Ib. when it closes. 



SIGNAL VALVE 



The accompanying cross-section shows the construction of 

 the signal valve, which weighs 16 Ib. The piece and reference 

 numbers of the valve and its parts are given in the accompany- 

 ing list. 



