AIR COMPRESSORS 41 



work poorly. Good valve oil is considered best for use in the 

 air cylinder. The oil may be fed to the cylinder by means of 

 a swab on the piston rod, or through the air-cylinder oil cups, 

 but it should never be fed through the air inlets, as it will 

 close the air passages, gum up the valves, reduce their lift, 

 and sooner or later result in overheating. Animal or vegetable 

 oils should not be used in the air cylinder, as they gum very 

 readily; also, mineral oils that have a low flashing point, as, 

 for instance, kerosense, should not be used in a hot cyl- 

 inder, as they generate an explosive gas that ignites at a 

 comparatively low temperature, and may, therefore, cause 

 trouble. 



LUBRICATING CROSS-COMPOUND COMPRESSORS 



Steam Cylinders. The steam-cylinder lubricator should not 

 be started until all condensation has escaped from the com- 

 pressor and the drain cocks closed. After closing the drain 

 cocks start the lubricator to feed in 10 or 15 drops of oil as 

 rapidly as possible, then regulate the feed to about 1 or 2 drops 

 per min. for each steam cylinder. No definite amount can 

 be specified, as the amount of lubrication required depends 

 on the work the compressor has to do, the quality of the steam, 

 condition of compressor, and so on. Keep the lubricator feed- 

 ing while the compressor is running. 



Air Cylinders. On account of the high temperatures devel- 

 oped by air compression, the variation between maximum 

 and minimum delivered air pressures, and the necessity of 

 preventing oil from passing into the system, one of the vital 

 problems in efficient compressor operation is to provide a 

 simple means for supplying lubrication to the air cylinders in 

 proper quantity and at regular intervals. 



To overcome the difficulties attending the lubrication of 

 the air cylinders of the 8$-in. and lOJ-in. cross-compound 

 compressors, two non-automatic oil cups are mounted on a 

 bracket, which, in turn, is connected to the air cylinders by 

 the necessary piping, thereby establishing an independent pas- 

 sage from each cup to the high- and low-pressure air cylinders 

 respectively. This cup, shown in the accompanying illustration, 

 is threaded for a f-in. tapped opening, while the upper end is 



