If too little water is introduced into an air cylinder during compression, the result is warm, moist air, and if too much water is used, it results in a surplus of power required to move a body of water which renders no useful service. The following table deduced from Zahner's formula gives the quantity of water which should be injected per cubic foot of air compressed in order to keep the temperature down to 104 degrees Fah. _________________________________________________________________________ | | | | |Weight of water |Weight of water | |to be injected at |to be injected at |Heat units devel-|68° Fah. to keep |68° Fah. to keep Compression |oped in 1 lb. |the temperature at|the temperature at by atmosphere |free air by |104° Fah. in lbs. |104° Fah. in lbs. of above a volume.|compression. |of water and per |water for 1 cubic | |lb. of free air. |foot of free air. _______________|_________________|__________________|____________________ | | | 2 | 3.702 | 0.734 | 0.056 3 | 5.867 | 1.664 | 0.089 4 | 7.406 | 1.469 | 0.113 5 | 8.598 | 1.701 | 0.131 6 | 9.570 | 1.891 | 0.145 7 | 10.398 | 2.063 | 0.158 8 | 11.109 | 2.204 | 0.167 9 | 11.740 | 2.329 | 0.179 10 | 12.301 | 2.440 | 0.188 11 | 12.813 | 2.542 | 0.195 12 | 13.278 | 2.634 | 0.202 13 | 13.706 | 2.719 | 0.209 14 | 14.102 | 2.798 | 0.215 15 | 14.471 | 2.871 | 0.223 _______________|_________________|__________________|____________________ Objections to water injection are as follows: (1) Impurities in the water, which, through both mechanical and chemical action, destroy exposed metallic surfaces. (2) Wear of cylinder, piston and other parts, due directly to the fact that water is a bad lubricant, and as the density of water is greater than that of oil, the latter floats on the water and has no chance to lubricate the moving parts. (3) Wet air arising from insufficient quantity of water and from inefficient means of ejection. (4) Mechanical complications connected with the water pump, and the difficulties in the way of proportioning the volume of water and its temperature to the volume, temperature and pressure of the air.