The Air Lift is one of the simplest methods of raising water from
underground sources. The main principle of its operation may be stated
thus: _air under pressure is conveyed into the lower end of the water
pipe through a suitable foot piece_.
[Illustration: FIG. 376.]
[Illustration: FIG. 377.]
City and town water works, asylums and hospitals, plantations, railway
water tanks, irrigation, private country houses, pumping mines, ice
manufactories, breweries, cold storage and packing houses, textile
mills, dye works, bleacheries, sewerage installations, dry docks,
seaside water works, stock farms; in fact, everywhere that clear and
abundant water is needed are opportunities for the application of the
Air Lift System of pumping water.
Nor is it alone for securing public water supplies that the Air Lift
is of special value. Within recent years the question of an abundant
and pure water supply for manufacturing, irrigation and other uses
has become one of equal importance. After an extensive experience,
two general systems have been devised for utilizing the water which
lies immediately below the surface of the ground. One, known as the
Deep-well Pump System, for which a working pump is used, and the other
the Air Lift System, which employs compressed air to raise the water,
either by means of its inherent expansive force or the difference in
specific gravity between compressed air and water.
NOTE.—Dr. Julius J. Pohle is admitted to be the original inventor
of this admirable and useful device. At first all systems by which
water or liquids were lifted by compressed air were more or less
extravagant, but with large experience and with improvements in air
compressor economy, the Air Lift has made valuable strides. Dr. Pohle
was actively associated with the Ingersoll Sargeant Co. until his
death, 1896, since which time his system has been further improved
and developed by a wider application and broader experience.
_Theory of the Air Lift._ Opinions differ as to the true theory of the
Air Lift. A common Air Lift case is one where there is a driven well in
which the water has risen approximately near the surface. In this well
is placed a large pipe for the discharge of the water, which is known
as an “_eduction pipe_.”
[Illustration: FIG. 378.]
This pipe does not touch the bottom of the well, but is elevated
above it so as to freely admit the water through its lower open end.
Alongside of this pipe, either on the outside or within, is a small
pipe properly proportioned and intended to convey compressed air to a
point near the bottom of the eduction pipe. It is usual to provide a
“foot-piece,” see Fig. 378, which forms a nozzle connecting the air
pipe with the water pipe, but in what is known as the “central pipe
system” this foot-piece is not used, the air pipe being placed within
the eduction-pipe to a point near the bottom, where it discharges the
compressed air into the water column.
Many neighborhoods are dependent upon well water, and there are few
districts where an ample supply is not to be secured from wells
properly made; this water is generally pure and wholesome. It is also
of uniform temperature the year round—cool and pleasant in the summer,
because the underground pipe and earth temperature remain uniformly
low. In winter, well water being warmer than that taken from ponds
and rivers, is not so apt to freeze, and, from all considerations of
temperature and purity, well water is greatly to be preferred. Many
cities located on rivers having a gravel bed formation find that, by
placing wells of suitable construction far enough back from the bank,
there is a natural filter bed, leaving the water clear, even when the
river itself is muddy. When river or other surface water is good the
wells may be sunk close to the edge, the water flowing down from the
top of the wells.
There are not many underground formations where wells should be
located close together. Such wells may affect or rob each other,
and it is usually best to spread them out on a line across what is
known to be the underground flow. Some finely creviced or tight rock
formations have a strong head with but little capacity, and wells in
such formations, if pumped hard, yield but little additional water.
They should be scattered and pumped moderately, maintaining a low and
economical lift. In other cases, one well in a group will give as much
water as all together, and more territory must be drawn on.
[Illustration: FIGS. 379-382.]
_The Pohle system of elevating liquids_ is shown in Fig. 377.
The process “consists in submerging a portion of an open-ended
eduction-pipe in a body of the liquid to be raised and continuously
introducing into the liquid within the lower part of the pipe a series
of bubbles of compressed gaseous fluid containing enough of the fluid
to expand immediately across the pipe and fill the same from side to
side, forming pipe-fitting piston-like layers at or just above the
point of their entrance into the pipe, whereby the column of liquid
rising in the pipe after the forcing out of the liquid first standing
in the latter is subdivided by the gaseous fluid into small portions
before it reaches the level of the liquid outside of the pipe, and a
continuously upward-flowing series of well-defined alternate layers of
gaseous fluid and short layers of liquid is formed and forced up the
pipe.”
The figures represent the apparatus in a state of action pumping
water, the shaded sections within the eduction-pipe, W, representing
water-layers and the intervening blank spaces air-layers.
At and before the beginning of pumping, the level of the water is
the same outside and inside of the discharge-pipe, W,—incidentally,
also, in the air pipe. Hence the vertical pressures per square
inch are equal at the submerged end of the discharge pipe. When,
therefore, compressed air is admitted into the air pipe, _a_, it must
first expel the incidental standing water before air can enter the
eduction-pipe, W. When this has been accomplished, the air-pressure
is maintained until the water within the eduction-pipe has been
forced out, which it will be in one unbroken column, free from
air-bubbles.
When this has occurred the pressure of the air is lowered or its bulk
diminished and adjusted to a pressure just sufficient to overcome
the external water-pressure. It is thus adjusted for the performance
of regular and uniform work, which will ensue with the inflowing air
and water, which adjust themselves automatically in alternate layers
or sections of definite lengths and weights. It will be seen in the
figures that the lengths of the water-columns (shaded) and air (blank
spaces) 1 and 1 are entered at the right of the discharge-pipe,
W; also, that under the pressure of two layers of water 1 and 2,
the length of the air column 2 is 6.71 feet long, and so on. The
lengths of aggregate water columns and the air columns which they
respectively compress are also entered on the right of the water-pipe.
On the left of the water-pipe are entered the pressures per square
inch of these water columns or layers. Thus the pressure per square
inch of column 1 is seen to be 1.74 pounds; that of 2, consisting of
two columns or layers 1 and 2 each 4.02 feet long, to be 3.49 pounds,
and that of 10, consisting of nine columns or layers of water 1 to 9,
inclusive, each 4.02 feet long, and one of 3.80 feet in length (viz.,
layer 10) to be 17.35 pounds, and the aggregate length of the layers
of water is 39.98 feet in a total length of ninety-one feet of pipe.
It will be noted that the length of pipe below the surface of the
water in the well is 55.5 feet, and that the difference between
this and the aggregate length of the water layers (39.98) is 15.52
feet—that is, on equal areas the pressure outside of the pipe is
greater than the pressure on the inside by the weight due this
difference of level, which is 47.65 pounds for the end of the
discharge pipe.
It is this difference of 15.52 feet, acting as a head that supplies
the water pipe, which puts the contents of the pipe in motion, and
overcomes the resistance in the pipe. In general the water layers are
equal each to each, and the pressure upon any layer of air is due to
the number of water layers above it.
Thus the pressure upon the bottom layer of air 10 in the figure is
due to all the layers of water in the pipe (17.35 pounds), and the
pressure upon the uppermost layer of air 1 is due to the single
layer of water, 1, at the moment of its discharges beginning—viz.,
1.74 pounds per square inch. As this discharge progresses this is
lessened, until at the completion of the discharge of the water layer
the air layer is of the same tension as the normal atmosphere.
_The air pipe_ is connected with an air receiver on the surface, which
is at or near the engine room, in which there is _an air compressor_.
This air pipe is provided with a valve on the surface. Before turning
on the air the conditions in the well show water at the same level on
the outside and inside of the eduction-pipe. At the first operation
there must be sufficient air pressure to discharge the column of water
which stands in the eduction-pipe.
This goes out _en masse_, after which the pump assumes a normal
condition, the air pressure being lowered and standing at such a
point as corresponds with the normal conditions in the well. This
is determined by the volume of water which the well will yield in a
certain time and the elevation to which the water is discharged.
NOTE.—This extended description of the principles upon which an air
lift operates—with its illustrations—is drawn almost word for word
from the original patent claims of Dr. Pohle. The occupation of
the space in the work is justified by the increasing importance of
this system of water supply and its practical applications in the
industrial world.
Year by year the world’s visible supply of coal—so long stored and
hidden away in the earth’s crust awaiting the advent of man—is
diminishing, next will dawn the age of air and water with electric
transmission.
After the standing water column has been thrown off by the pressure
the air rises through the water reduces its weight, with the result
that the water is expelled as fast as the well supplies it, _the water
outside the pipe, acting as a head, flows into the discharge pipe by
the force of gravity_.
The machinery necessary for a system of pumping comprises, 1, _an air
compressor_; 2, a receiver to store and equalize the pressure; 3, the
head piece and foot piece for the well; and, 4, the necessary piping
for the air supply and water discharge.
[Illustration: FIG. 383.]
With an available supply of air under pressure _the pump proper
consists of simply a water discharge and air pipe_, the latter arranged
and properly controlled to inject air into the former at the point of
proper submersion. It is readily seen that the apparatus is so simple
that as a pump it cannot get out of order; in cases, where mud, sand or
gritty material is encountered, it will handle such matter _with the
water_ and without injury to the system, as nothing comes in contact
with the moving parts.
[Illustration: FIGS. 384, 385.]
Absence of all obstructing mechanism in the wells allows each to be
operated to its full capacity. Production, therefore, does not depend
upon the pump, but rather upon the capacity of the well to yield water;
the natural yield of wells is often increased by this process of using
compressed air admitted close to the bottom of the discharge pipe, the
water is set in motion at a considerable depth, and by this action the
well is “cleaned.”
_Purification is effected by aeration during the process of pumping_,
the absorption of air by the water preventing the formation of
unsanitary growths.
_Three styles of well heads_ are shown in Figs. 383, 384 and 385.
_The deflector head_, Fig. 383, is attached to the well casing or
discharge pipe by standards. This form of head piece is generally used
where the water is to be raised to the surface, or just below the
surface into a tank, where the air is allowed to separate itself, and
the water flows to some central collecting reservoir, where it is used
or forced by means of an ordinary pump to a higher elevation. The head
piece offers no obstruction to the discharged water.
_The offset discharge_, Fig. 384, is adapted to situations where the
water is to be pumped by air direct from the well to some elevation
above the well.
_The elbow discharge_, Fig. 385, shows the common form of well head
known as the elbow head, adapted to be used either as a cap for the
well casing itself, or used in connection with a suitable discharge
pipe.
_The foot piece, or nozzle_, which regulates the admission of air to
the discharge pipe at the point where the air comes in contact with the
water, thereby makes it possible to carry air at full pressure to the
end of the air pipe, and utilizes the energy due to the velocity of the
discharged air.
_After a well is once regulated or balanced_ there is but little
occasion to move the adjusting wheel or valve, the starting and
stopping of the flow of any particular well being accomplished by means
of an ordinary valve or plug cock on the air pipe at or adjacent to the
well.
_One Central Station of suitable capacity will operate several wells
no matter how far apart._ The necessity of maintaining a number of
separate pumping plants is thus done away with, and in taking a supply
of water from an underground source the wells can be located without
reference to the power plant, and at such distances apart as will best
maintain the highest average pumping level.
Although the principle of the action governing all pumps of this
description is so simple, there are a number of factors having a direct
influence upon the performance of the pump, which have been expressed
in the following terms by a well-known expert:
(_a_) Depth of submersion of point of air discharge below still water
surface.
(_b_) Velocity of water at point of air discharge.
(_a_) and (_b_) determine the necessary air pressure. If (_a_) is
constant, the pressure decreases when (_b_) increases.
(_c_) Area of main, or water discharge pipe.
(_d_) Net lift to point of water discharge, including velocity head
at that point.
(_e_) Volume of air (at atmospheric pressure) discharged per unit of
time.
(_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.
[Illustration: FIG. 386.]
The air compressor forces the air down the inside pipe, which is 1-1/4″
in diameter. The outside pipe, which is 3″ in diameter, has its lower
end submerged in the well. The compressed air forces a rising column of
air mingled with water in the outer pipe to the supply tanks, which are
situated at the top of the building.
_Direct Air Pressure Pumps._ This term is applied to that class of
pumps in which the liquid is taken into an air tight vessel and then
driven out through pipes to a higher level by the application of
compressed air directly on the surface of the liquid in the tank, thus
dispensing with cylinders, pistons, valves, glands, etc., of the more
common class of pumps.
[Illustration: FIG. 387.]
Fig. 387 shows the parts of the pump; its operation is as follows:
Suppose the compressor to be in operation and the switch set as in the
figure; the air will be drawn out of the right tank and forced into the
left tank, and in so doing will draw water into the former and force it
out of the latter. The charge of air in the system is so adjusted that
when one tank is emptied the other is filled, and at that moment the
switch will be automatically thrown, reversing the pipe connections and
thereby reversing the action in the tanks.
_The switch_ is a simple mechanism placed on the air pipes near the
compressor. It can be automatically operated in one of three ways:
_First_, by means of the suction which occurs in the intake pipe to
the compressor, when water is drawn above its outside level in one of
the tanks. The details of the mechanism to utilize this suction are
very simple.
_Second_, by a mechanism, that will throw the switch at some assigned
number of strokes of the compressor, the proper number being that
which will empty one tank and fill the other. This can be closely
computed beforehand and can be determined exactly by test when
commencing operation and the switch adjusted accordingly.
_Third_, by an electrically controlled mechanism, the circuit being
made and broken by a pressure gauge on the intake of the compressor.
The Pneumatic Engineering Co. are the makers of this apparatus, named
_the Harris System_ of raising water by direct pressure.
THE STEAM
FIRE ENGINE
[Illustration: FIG. 388.]