AIR COMPRESSORS 21 



When this compressor is ordered complete, for industrial, or 

 other than railroad-brake service, order should so state, and 

 specify Piece No. 19,392. When so ordered, packing and cap- 

 nut wrench, Piece No. 1,935 (instead of Piece No. 15,551), 

 air- valve-seat wrench, Piece No. 7,188, air- valve-cage wrench. 

 Piece No. 7,189, and wrench for f-in. nuts, Piece No. 11,392, are 

 included with the compressor without extra charge. 



Operation of Steam Cylinder.^When the pump is at rest, the 

 pistons generally settle to the bottom of their cylinders and 

 the reversing plate strikes against the button on the reversing 

 rod and pulls the reversing valve into lowest position. When 

 steam is admitted to the pump, it enters the main-valve bush- 

 ing, and, as the area of the large piston is greater than that 

 of the small piston, forces the main valve to the right, passes 

 into the cylinder below the piston, and forces the piston 

 upwards. Any steam above the piston will exhaust to the 

 atmosphere through the exhaust pipe. As the steam piston 

 nears the end of its upward stroke, the top of the reversing 

 plate strikes the shoulder on the reversing rod and forces the 

 reversing valve upwards. This permits steam to enter the 

 chamber at the right of the large piston and balance the 

 pressure on the piston 20 of the main valve, and the pressure 

 on this piston 20 then forces the main valve and the slide 

 valve to the left until the cavity of the slide valve connects 

 the steam to the lower end of the cylinder port with the 

 exhaust port. The steam port to the upper end of the cylin- 

 der is uncovered and steam flows into the steam cylinder 

 above the steam piston, forcing the piston downwards. The 

 steam below the piston flows through the steam ports and the 

 cavity in the slide valve, and out of the exhaust. As the piston 

 nears the end of its downward stroke, the bottom of the revers- 

 ing plate strikes the button on the reversing rod and pulls the 

 rod and reversing valve to their lowest positions. This move- 

 ment exhausts the steam from the chamber to the right of the 

 piston 20 and allows the main valve to move the slide valve to 

 the right, thus permitting steam to pass underneath the piston 

 and force it upwards. 



Operation of Air Cylinder. When the air piston makes an 

 upward stroke, it produces a partial vacuum below it, while 



