THE AIR LIFT PUMP.

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.

Fig. 376.

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 abundantand 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.”

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 usualto 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.

Figs. 379-382.

The Pohle system of elevating liquidsis 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 thepipe 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.

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.

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 pipeis connected with an air receiver on the surface, which is at or near the engine room, in which there isan 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 outen 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.

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.

Fig. 383.

With an available supply of air under pressurethe 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 apparatusis 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 matterwith the waterand without injury to the system, as nothing comes in contact with the moving parts.

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 admittedclose 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 headsare shown in Figs.383,384and385.

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 balancedthere 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.

(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.

(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 thePractical Engineeras shown in the sketch, Fig.386.

Fig. 386.

The air compressor forces the air down the inside pipe, which is 11⁄4″ 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.

Fig. 387.

Fig.387shows 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 switchis 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 switchis 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, namedthe Harris Systemof raising water by direct pressure.

Back to Index Next