AIR COMPRESSORS 87 



iVo. Name of Part 



Regulating nut for maximum-pressure 

 head. 



Regulating spring for maximum-pressure 

 head. 



Diaphragm, complete, for maximum-pres- 

 sure head, includes 32, 33, 34, 35, and 36. 



Diaphragm ring. 



Vent -port screw. 



Spring box, for excess-pressure head. 



Spring-box extension for excess-pressure 

 head. 



Check-nut for excess-pressure head. 



Regulating nut for excess-pressure head. 



Regulating spring for excess-pressure head. 



Diaphragm, complete, for excess-pressure 

 head, includes 32, 33, 34, 35, and 36. 



Strainer. 



Union swivel, f in. O. D. copper pipe. 



Union nut. 



Diaphragm nut. 



Diaphragm valve. 



Diaphragm washer. 



Diaphragm-valve spring. 



Diaphragm, 2 pieces, each. 



Union connection, complete, includes 37, 

 38, and 39. 



Union nut. 



Union swivel. 



Union stud. 



Union swivel, J-in. iron pipe. 



Operation of Governor. The duty of the SF pump governor 

 is to so restrict the speed of the pump, when the desired main- 

 reservoir pressure is obtained, as to prevent this pressure from 

 rising any higher. During most of the trip, the brake valve 

 is carried in running position to keep the brakes charged. 

 But little excess pressure is then needed, and the governor 

 regulates the main-reservoir pressure to about 20 Ib. above the 

 brake-pipe pressure, thus making the work of the pump easier. 

 When the brakes are applied (lap position of the brake valve 

 following the use of its service position) a high main-reservoir 

 pressure is needed to insure the prompt release and recharge 

 of the brake. Therefore, as soon as the use of lap, service, or 

 emergency positions is commenced, the governor allows the 

 pump to work freely until the maximum main-reservoir pressure 

 is obtained. Again, when the brake-pipe pressure is changed 



