AIR COMPRESSORS 93 



cock or small pipe connection at its lowest point by means of 

 which all residue may be drawn off at frequent intervals, as 

 water or oil collecting will soon materially decrease the air- 

 storage capacity of the reservoirs. 



Fig. 1 shows the welded pipe, that is, steel tubing with heads 

 welded in, furnished in diameters of 16 in. and under, and 



FIG 1 FIG. 2 



Fig'. 2 the riveted type, made of steel sheets with longitudinal 

 seam and heads riveted, furnished in diameters of 18$ in. and 

 over. The reservoirs are tested to a pressure of 140 Ib. They 

 are built to the W. A. B. standard specifications for railroad 

 service and designed for pressures up to 125 Ib. per sq. in. The 

 accompanying table gives the standard sizes of these reser- 

 voirs; they may be placed either vertically or horizontally, as 

 preferred. In either case, however, it is advisable to have 

 the air inlet and outlet near the top and on opposite sides of 

 the reservoir, but not directly opposite each other, and the 

 drain cock should be located at the lowest point. 



Main Reservoir. The standard main reservoir is a store 

 chamber in which a large supply of compressed air is main- 

 tained to charge the brake pipe and auxiliaries; to release 

 brakes, if set, by charging the brake pipe to a higher pressure 

 than that in the auxiliaries; and to feed any brake-pipe leaks 

 while the brakes are released. Also, it often provides air for 

 operating sand blowers, bell ringers, blow-off cocks, water 

 scoop, and other devices with which the engine is equipped. 

 The usual main-reservoir pressure is 90 Ib., but this is exceeded 

 in mountainous districts when handling very long trains, when 

 the train is equipped with the high-speed brake, or when the 

 Westinghouse special attachment for controlling heavy trains 

 on long down grades is used, 



