ENGINEER'S BRAKE VALVES 145 



of piston 6, which allows the piston spring to move piston 6 

 and the supply valve to closed position. In this position no 

 air can feed into the brake pipe, since the supply port is closed. 



The parts of the feed-valve remain in these positions as 

 long as the brake-pipe pressure remains at 70 Ib. Any reduc- 

 tion of brake-pipe pressure, however, allows the regulating 

 spring 19 to expand and unseat the regulating valve; pressure 

 in the chamber to the right of piston 6 is then immediately 

 reduced to brake-pipe pressure, so that the greater pressure 

 of the air in the chamber to the left of piston 6 forces the piston 

 to open position. 



Regulation of Feed-Valve. If the feed-valve does not 

 regulate brake-pipe pressure to the proper amount, it can be 

 made to do so by adjusting the tension of the regulating spring 

 by means of the regulating nut 20. If it maintains a pres- 

 sure below the standard, slowly turn the regulating nut to the 

 right until the tension of the spring is sufficiently increased 

 to give proper regulation. If it maintains too high a pressure 

 place the brake valve in service position and reduce the brake- 

 pipe pressure several pounds below standard; then turn the 

 regulating nut to the left so as to relieve the spring of a little 

 of its tension, place the brake valve in running position, and 

 note the pressure that is then maintained. If still too high, 

 proceed as before, and continue until the feed-valve is properly 

 adjusted. In order to turn the regulating nut 20, the check- 

 nut %l must first be removed. After the regulating spring has 

 been properly adjusted, the check-nut must be replaced. 



B-6 DOUBLE-PRESSURE FEED-VALVE 

 Piece and Reference Numbers. The B-6 double-pressure 

 feed-valve, shown in Fig. 2, has superseded the B-4 double- 

 pressure feed-valve, and is a part of, and is regularly supplied 

 with, the ET locomotive brake equipments; its weight is 

 10J Ib. The piece number of the feed-valve, complete, with- 

 out pipe bracket or gasket, is 18,477; with F crossed-passage, 

 pipe bracket and gasket, complete, 18,478; and with H direct- 

 passage, pipe bracket and gasket, complete, 18,479. The 

 piece and reference numbers of the various parts are given in 

 the accompanying list. 

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