(f) Ratio of expansion of air as it rises through the main pipe; (f) may be considerably modified by the temperature of the water.
(g) Total volume of air in main pipe at any instant. This determines the specific gravity of the discharging column.
(h) The volume of each individual bubble within the main.
Letters are for reference only and do not indicate the order of importance nor of effect.
It was at first supposed that in all Air Lift cases the water was discharged because of the aeration of the water in the eduction-pipe, due to the intimate co-mingling of air and water. Bubbles of air rising in a water column not only have a tendency to carry particles of water with the air, but the column is made lighter, and, with a submergence or weight of water on the outside of the eduction-pipe, there would naturally be a constant discharge of air and water. This is known as the Frizell System, and where the lifts are moderate—that is, where the water in the well reaches a point near the surface—it is very likely that the discharge is due to simple aeration.
Most air lift propositions are deep-well cases—that is, the water is lifted a distance greater than 25 feet; and just in proportion as the lift is increased do we get away from the aerated form idea, and so when the air pressure is greater than the head of water, a certain volume of compressed air is received into the eduction-pipe, the water in this pipe is at that time moving rapidly upward; that is, its momentum has been established. Hence the air takes up this velocity and goes upward with the water from the energy received from the elasticity of the air due to its compressor.
A practical example of the successful working of an air compressor for raising water from a driven well 319 feet is described and illustrated by the Practical Engineer as shown in the sketch, Fig. [386].
Fig. 386.