76 AIR COMPRESSORS 



is now obsolete and is not furnished with full sets of brake 

 equipment; repair parts, however, may be obtained. Type 

 S-4 is considered standard size for single governors, as with 

 the high steam pressures carried on modern locomotives, the 

 1-in. steam pipe and governor is believed to meet all present 

 requirements. This governor, however, has been replaced by 

 the type SF-4 duplex governor for standard locomotive brake 

 schedules. The type S-5 governor is no longer recommended 

 for use ir> connection with standard locomotive brake schedules, 

 having been replaced by the SF-5 duplex governor. The type 

 S-6 governor is furnished for any service for which it is 

 suitable. It is recommended for all equipments that include two 

 11-in. or two Sj-in. simple, cross-compound air compressors. 



The SD duplex governor is made in two sizes: the SD-4 

 (1-in.) governor and the SD-5 (lj-in.) governor. The SD-4 

 type replaced the S-4 governor as standard for one 9|-in. 

 compressor; and this, in turn, has been replaced by the SF-4 

 governor. The SD-4 governor is still furnished when specified. 

 The SD-5 governor has been superseded by the SF-5 governor 

 for locomotive equipments specifying two compressors; it can 

 be obtained, however, when specified. The SF duplex governor 

 is made in two sizes: the SF-4 (1-in.) governor supplied with 

 all locomotive brake equipments requiring one 9^-in. air com- 

 pressor and the SF-5 (lj-in.) governor supplied with all loco- 

 motive brake equipments requiring two 95-in., one 11-in., or 

 one Si-in. cross-compound pump. 



The substitution of the duplex for the single governor was 

 to facilitate the subsequent application of the high-speed 

 brake in passenger service and the high-pressure control 

 apparatus in freight service. Also, it made possible the duplex- 

 main-reservoir regulation system when connected up as illus- 

 trated in Figs. 3 and 5. 



WEIGHTS OF COMPRESSOR GOVERNORS 



S-3 .............. 11 SD-4 ............... 19 



S-4 ................ 13J SD-5 ............... 25 



S-5 .. ____ 19* SF-4 ............... 19 



S-6 .......... 23* SF-5 .............. 25 



