88 AIR COMPRESSORS 



from one amount to another by the feed- valve, as where a 

 locomotive is used alternately in high-speed-brake and ordinary 

 service, the governor automatically changes the main-reser- 

 voir pressure to suit, and at the same time maintains the other 

 features just described. Also, before commencing and during 

 the descent of steep grades, this governor enables the engineer 

 to raise and maintain the brake-pipe pressure about 20 Ib. 

 above the feed-valve regulation merely by the use of release 

 position of the automatic brake valve. 



Air from the main reservoirs flows through the automatic 

 brake valve (when the latter is in release, running, or holding 

 position) to the automatic brake- valve connection 30 into the 

 chamber below diaphragm 36. Air from the feed-valve pipe 

 enters at the feed-valve connection 39 to the chamber above the 

 diaphragm 36, thus aiding the pressure of the regulating spring 

 27 in holding the diaphragm down. As this spring is adjusted 

 to about 20 Ib., this diaphragm will be held down until the 

 main-reservoir pressure in the chamber below the diaphragm 

 slightly exceeds the combined air and spring pressure in the 

 chamber above the diaphragm. At such time, the diaphragm 

 will be raised, unseat its pin valve, and allow air to flow to the 

 chamber above the governor piston, forcing the latter down- 

 wards, compressing its spring and restricting the flow of steam 

 past steam valve 5 to the point where the pump will just supply 

 the leakage in the brake system. When the main-reservoir pres- 

 sure in chamber 36 becomes reduced, the combined spring and 

 air pressures above the diaphragm force the diaphragm down, 

 seating its diaphragm valve. As the chamber above the gov- 

 ernor piston is always open to the atmosphere through the 

 small vent port, the pressure in that chamber will then escape 

 to the atmosphere and allow the piston spring, and steam 

 pressure below the steam valve 6, to raise the valve and the 

 governor piston. Since the connection from the main reser- 

 voir to the chamber below the diaphragm 36 is open only when 

 the handle of the automatic brake valve is in release, running, 

 or holding positions, in the other positions this governor head 

 is cut out. The main-reservoir connection in the maximum- 

 pressure head should be connected to the main-reservoir cut- 

 out cock, or to the pipe connecting the two main reservoirs, so 



