_______________________________________________________

__________________
|                 |                  |
|                 |Weight of water   |Weight of water
|                 |to be injected at |to be injected at
|Heat units devel-|68 deg.  Fah. to keep  |68 deg.  Fah. to keep
Compression    |oped in 1 lb.    |the temperature at|the temperature at
by atmosphere  |free air by      |104 deg.  Fah. in lbs. |104 deg.  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.

(5) Loss of power required to overcome the inertia of the water.

(6) Limitations to the speed of the compressor, because of the liability to break the cylinder head joint by water confined in the clearance spaces.

(7) Absorption of air by water.

Before the introduction of condensing air receivers, wet air resulting in freezing was considered the most serious obstacle to water injection; but this difficulty no longer exists, as experience has conclusively demonstrated that a large part of the moisture in compressed air may be abstracted in the air receiver.  Even in the so-called dry compressors a great deal of moisture is carried over with the compressed air, because the atmosphere is never free from moisture.  This subject will be referred to more fully when treating of the transmission of compressed air.