402 



TRAIN AIR-SIGNALING SYSTEM 



The air-signal apparatus on the engine, Fig. 2, consists of 

 the signal valve, signal whistle, and pressure-reducing valve. 

 A f-in. pipe leads from the main reservoir to an air strainer, 

 then to the reducing valve, thence leads to, and connects 

 with, the T-fitting 5 in the signal pipe. Air from the main 

 reservoir can thus pass through the pressure-reducing valve, 

 thence into the signal pipe and signal valve, but at a 

 reduced pressure. A pressure of 40 Ib. is usually maintained 

 in the signal system, and the duty of the reducing valve is to 

 diminish the pressure from 90 Ib. (main-reservoir pressure) to 

 the required pressure for use in the signal 

 system. 



SIGNAL WHISTLE 



The signal whistle, Fig. 1 (a small whistle 

 located in the cab, as close to the engineer as 

 practicable) , is piped to the signal valve, and 

 it is the operation of the latter 

 that causes the whistle to blow. 

 The piece number of the whistle 

 complete, when tapped for J-in. 

 pipe, is 2,804. A cross-section 

 of the whistle is shown in Fig. 2. 

 When the conductor pulls the 

 signal cord in one of the cars, he 

 opens the discharge valve on that 

 car and allows some of the air 

 in the main signal pipe to escape 

 to the atmosphere, thus redu- 



FlG. 1 



FIG. 2 



cing the signal-pipe pressure. The reduction in pressure oper- 

 ates the signal valve on the engine, which discharges a small 

 quantity of air through the signal whistle in the cab, thus 

 causing it to sound a short blast. Each time the cord is 

 pulled, the signal whistle gives a blast. 



The bowl 1 forms the base of the whistle and connects with 

 the whistle pipe at X. The passage a' and port a form a 

 passage from the whistle pipe into chamber A. The disk 2 

 deflects the escaping air and makes it strike the edge of the 



