Aer is the first element in many compound words of Greek origin meaning air, the air, atmosphere; in this connection it is combined with motor, defined as a machine which transforms the energy of water, steam, or electricity into mechanical energy—in this instance, is meant the changing of the power of moving air or wind into mechanical energy. Wind is air put in motion. There are two ways in which the motion of the air may arise. It may be considered as an absolute motion of the air, rarefied by heat and condensed by cold; or it may be only an apparent motion, caused by the superior velocity of the earth in its daily revolution. When any portion of the atmosphere is heated it becomes rarefied, its specific gravity is diminished, and it consequently rises. The adjacent portions immediately rush into its place to restore the equilibrium. This motion produces a current which rushes into the rarefied spot from all directions. This is what we call wind. Meteorology is the science which treats of the atmosphere and its phenomena, particularly of its variations of heat and cold, of its winds, etc. This is the great division of science to which one has to turn when searching for the first principles relating to the operation of aermotor pumps. The vast volumes of air which flow “hither and yon” are controlled by physical laws which act as accurately and unceasingly as those which control and hold in check the seemingly solid substance of the earth itself. Note.—The portions north of the rarefied spot produce a north wind, those to the south produce a south wind, while those to the east and west in like manner, form currents moving in opposite directions. At the rare spot, agitated as it is by winds from all directions, turbulent and boisterous weather, whirlwinds, hurricanes, rain, thunder and lightning, prevail. This kind of weather occurs most frequently in the torrid zone, where the heat is greatest. The air, being more rarefied there than in any other part of the globe, is lighter, and, consequently, ascends; that about the polar regions is continually flowing from the poles towards the equator, to restore the equilibrium; while the air rising from the equator flows in an upper current towards the poles, so that the polar regions may not be exhausted. To sum up all observations, it can be said with truth that the sole force immediately concerned in causing the movements of the atmosphere, is gravitation. So far as the prevailing winds are concerned it has been shown that where pressure is high, that is to say, where there is a surplus of air, out of such a region winds blow in all directions; and, on the other hand where pressure is low, or where there is a deficiency of air, towards such a region, winds blow from all directions in an in-moving special course. This outflow of air currents from a region of air pressure upon a region of low pressure is reducible to a single principle, as already stated, viz., the principle of gravitation. A regular east wind prevails about the equator, caused in part by the rarefaction of the air produced by the sun in his daily course from east to west. This wind, combining with that from the poles, causes a constant north-east wind for about thirty degrees north of the equator, and a south-east wind at the same distance south of the equator. From what has now been said, it appears that there is a circulation in the atmosphere; the air in the lower strata flowing from the poles towards the equator, and in the upper strata flowing back from the equator towards the poles. It may be remarked, that the periodical winds are more regular at sea than on the land; and the reason of this is, that the land reflects into the atmosphere a much greater quantity of the sun’s rays than the water, therefore that part of the atmosphere which is over the land is more heated and rarefied than that which is over the sea. This occasions the wind to set in upon the land, as we find it regularly does on the coast of Guinea and other countries in the torrid zone. There are certain winds, called trade-winds, the theory of which may be easily explained on the principle of rarefaction, affected, as it is, by the relative position of the different parts of the earth with the sun at different seasons of the year, and at various parts of the day. A knowledge of the laws by which these winds are controlled is of importance to the mariner. When the place of the From its importance in practical meteorology Buys Ballot’s law may be stated in these two convenient forms. (1) Stand with your back to the wind, and the center of the depression or the place where the barometer is lowest will be to your left in the northern hemisphere, and to your right in the southern hemisphere. This is the rule for sailors by which they are guided to steer with reference to storms. (2) Stand with the high barometer to your right and the low barometer to your left, and the wind will blow on your back, these positions in the southern hemisphere being reversed. It is in this form that the prevailing wind of any part of the globe may be worked out from the charts. It is as a source of energy, to be classified with heat, weight of liquids, electricity, etc., that air in motion (as in a windmill) has a place as a prime mover. Prime movers, or receivers of power, are those pieces or combinations of pieces of mechanism which receive motion and force directly from some natural source of energy. The point where the mechanism belonging to the prime mover ends and that belonging to the train for modifying the force and motion begins may be held to include all pieces which regulate or assist in regulating the transmission of energy from the source of energy. The useful work of the prime mover is the energy exerted by it upon that piece which it directly moves; and the ratio which this bears to the energy exerted by the source of energy is the efficiency of the prime mover. In all prime movers the loss of energy may be divided into two parts, one being the unavoidable effect of the circumstances under which the machine necessarily works in the case under consideration; the other the effect of causes which are, or may be, capable of indefinite diminution by practical improvements. Those two parts may be denominated as necessary loss and waste. The efficiency which a prime mover would have under given circumstances if the waste of energy were altogether prevented, and the loss reduced to necessary loss alone, is called the maximum or the theoretical efficiency under the given circumstances. In windmills, the air, being in motion, presses against, and moves four or five radiating vanes or sails, whose surfaces are approximately helical or screw shape, their axis of rotation being parallel, or slightly inclined in a vertical plane, to the direction of the wind. The velocity of the wind determines its pressure, and the pressure of the wind against the sails of the windmill determines the power developed by the mill. A mill of small diameter acted upon by a high pressure develops as much power as a large mill working under a lower pressure. The mean average velocity of the wind for the entire United States is very nearly eight miles per hour. However, for large areas such as the great plains east of the Rocky Mountains, the mean average is about eleven miles per hour, and yet in certain small areas situated in the mountainous districts the mean average velocity is as low as five miles per hour. Therefore, in selecting and loading a mill, reference should be had to the wind velocity prevailing in that particular locality. In general, windmills loaded to operate in ten-mile winds can be depended upon to furnish a sufficient supply of water. The variations in the velocity and pressure of the wind are considerable even within a brief time, and sometimes sudden and extreme. Winds of 100 miles per hour and upwards are on record. A very violent gale in Scotland registered by an excellent anemometer a pressure of 45 lbs. per square foot. During the severe storm at London, the anemometer at Lloyd If the wind were to blow continuously a very small windmill would suffice to do a large quantity of work and no storage capacity would be required, but when it does blow it is “free” and experience dictates that a mill shall be erected sufficiently large to pump enough water, when the wind does blow, to last over, with the assistance of ample storage capacity. Average hourly velocity of the wind at following stations of the U. S. Weather Bureau, given in miles per hour:
Note.—Windmills are erected to be operated by the lightest winds. A wind which will carry off smoke will move a windmill; and the absence of a wind of this force means a perfect calm. Mr. Corcoran says: “My experience of thirty years teaches that a calm has seldom, if ever, held sway in this part of the world for a longer period than three days. Consequently, with a tank to hold a three days’ supply, it becomes possible to pass over any number of calms.” Fig. 460. WIND POWER PUMPS.Windmills can be divided into two general classes according to the inclination of the shaft: 1, Horizontal mills, in which sails are so placed as to turn by the impulse of the wind in a horizontal plane, and hence about an axis exactly vertical; and, 2, vertical mills, in which the sails turn in a nearly vertical plane, i.e., about an axis nearly horizontal. On account of the many disadvantages connected with the horizontal windmill, it is seldom brought into use, being employed only in situations in which the height of the vertical sails would be objectionable, and this is liable to occur only in extraordinary cases. In this kind of mill six or more sails, consisting of plain boards, are set upright upon horizontal arms resting on a tower and attached to a vertical axis, passing through the tower at its middle part. If the sails are fixed in position, they are set obliquely to the direction in which the wind strikes them. Outside of the whole is then placed a screen or cylindrical arrangement of boards intended to revolve, the boards being set obliquely and in planes lying in opposite courses to those of the sails. The result is, from whatever direction the wind may blow against the tower, it is always admitted by the outer boards to act on the sails most freely in that half of the side it strikes, or from which the sails are turning away, and it is partly, though by no means entirely, broken from the sails which in the other quadrant of the side are approaching the middle line. Fig. 461. Note.—The great objections to the horizontal windmill are: first, that only one or two sails can be effectually acted upon at the same moment; and, secondly, that the sails move in a medium of nearly the same density as that by which they are impelled, and that great resistance is offered to those sails which are approaching the middle. Hence with a like area of sails the power of the horizontal is always much less than that of the vertical mill. The illustration on page 184, Fig. 460, is a representation of the Corcoran windmill: it contrasts most interestingly with the same apparatus shown in Fig. 459—a windmill of the early part of the 17th century. The figure below, 462, exhibits in detail the rear view of the Corcoran mill with the governor. As the speed of the wheel increases it swings the “tail” around, so as to bring the wheel at an angle with the direction of the wind; the latter failing to strike the blades squarely communicates less force, and in consequence the speed is diminished; in case of a very high wind the tail turns so as to present the wheel almost edgewise towards the direction of the blast. Note.—A windmill of this type was erected at a station on the Long Island R. R. to pump 5,000,000 gallons of water yearly. In order to test the work of the windmill, a water meter was attached to the pump during six months, and it was shown that the average work of the windmill had been 22,425 gallons per day, 4,260,750 gallons during the time stated and an average rate of 8,000,000 gallons per year. The weight of water pumped was 16,168 tons gross and was raised to a height of 66 feet, and the work was done without mishap with little attention given to the pumping machinery. Fig. 462. Fig. 461 represents a Corcoran double action suction force pump. The base is hollow and contains the suction and discharge valves; a flange at the left-hand side receives the suction pipe while a corresponding flange on the right-hand side connects with the discharge pipe. An air chamber is attached to Fig. 463. Fig. 463 is intended to represent an Ideal steel tank tower; the tank is herein located near the top. A force pump is used where water is delivered into an elevated tank as in this case; a lift pump is employed to discharge water at the spout and not to elevate above it. The common term “Windmill pump” distinguishes a wind power pump from a hand pump, the difference being in an extension of the piston rod above the upper guide with a hole for connection with the pump rod from the windmill. Such a pump, with the “pit-man” extending from the pump upwards into the tower, is shown in Fig. 465. This figure is introduced to show the tank connections with a regulator on the base of a four-post tower. The float in the water tank throws the mill in or out of gear according as the water rises or falls in the tank. When the tank is filled with water it pulls the mill out of gear and stops the pump; as a result there can be no overflow or waste. The tank is thus not allowed to become empty and permit its drying apart, inducing leakage. But through the medium of the float in the tank, when the water has been lowered but a few inches, the mill is again put in gear and the tank refilled to the desired height, at which the float is set. Note.—These have long been erroneously termed windmill pumps dating to the time when wind furnished the power for driving the grist mills used in grinding grain, etc. More properly they may now be named windmotors or airmotors. The syphon pump here illustrated, Fig. 464, is used to force water from shallow wells to elevations. The cylinder or barrel is situated within the standard and very convenient for inspection. It has an air chamber which is detachable. Fig. 464. The subject of tanks and cisterns is one almost vital to the successful operations of ordinary windmills, owing to the irregularity of the power to be utilized by the use of aermotors. In another part of this work this important subject will be further explained and illustrated. One of the most valuable special features of this windmill is its governor. It is so contrived that it insures immunity of the mill from injuries in destructive storms. It consists of a steel coiled spring of great resiliency, located at the base of the vane frame. Its strength is of such a character as to hold the wheel in the teeth of the wind under all ordinary conditions but is sure to yield under greater pressure. Fig. 465. USEFUL DATA Table I.
Table II.
Table III.
Table IV.
Table V.
Table VI.
Table VII.
The preceding tables are based upon tests of the Sampson windmill as compiled by its makers, The Stover Manufacturing Co.; they deserve careful study by those planning the introduction of aermotors. The power of a windmill depends—first, on the diameter of the wheel; and second, on the velocity of wind. To increase the diameter of the wheel is to increase its power in proportion to the area of the squares. Table I gives the horse-power of several sizes of mills working in a fifteen-mile wind: if the wind velocity be increased or diminished, the power of the windmill will increase or decrease in the ratio of the squares of the velocity. Table V will show the comparative power or force of the wind in velocities from eight to forty miles per hour for each square foot of surface. Rules for approximately determining size of windmill to use. The daily water consumption must be given as a basis for calculation. Divide this by 8 to find the hourly capacity of windmill, as if loaded aright the mill will pump on an average eight hours daily. Multiply the quotient by total water lift in feet and with the co-efficient given in Table II. The product will in Table I show what mill to use. The size of the cylinder and discharge pipe will be found in Table III. Fig. 466. Table I gives the maker’s number of the pumping mill, and the number of gallons each will raise one foot high per hour, with a wind having a velocity of fifteen miles per hour. Example: No. 9 pump will raise 24,000 gallons of water one foot high in one hour. Now if the water is to be raised 50 feet then by dividing 24,000 by 50 the quantity raised becomes 480 gallons per hour. From Table V it will be seen also that a wind velocity of fifteen miles per hour develops a power three times as great as an eight-mile wind, and a twenty-mile wind is twice as powerful as a fifteen-mile, or six times that of an eight-mile. Hence, a small increase in velocity greatly increases the power of the windmill, while a low velocity gives but little working force. From Table VI it is seen that a twenty-five mile wind gives six times as much power as a ten-mile wind, but really gives twenty-six times the net efficient power of the ten-mile wind, therefore it will not be proper to calculate on using a power windmill in as low a velocity as ten miles. From Table VII it is seen that the net efficient result is six times as great in a fifteen-mile wind as in a ten-mile wind, and sixteen times greater in a twenty-mile wind than in a ten-mile wind. Therefore, power windmills give best results when working in fifteen to twenty-five mile winds. A 12-foot power windmill working in a fifteen-mile wind will do more work than an average horse, and when working in a twenty-mile wind will do more work than two average horses. Example.—A person in Atlanta, Ga. uses 2,600 gallons of water daily. He has a well in which the water stands 30 feet from ground level. To obtain pressure, the water is to be elevated into a tank 50 feet above ground. 2,600 ÷ 8 = 325 gallons to be pumped hourly when windmill works. Average wind velocity at Atlanta is 9 miles per hour, answering to coefficient 1.4 in Table II, and total water lift is 30 + 50 = 80 feet. 325 × 1.4 × 80 = 36,400 gallons. If first estimate of 2,600 gallons daily was liberal, so that for instance 2,400 gallons would be sufficient, Table I shows that a 10-foot mill can be used, but to keep on the safe side, choose a 12-foot mill. 325 gallons hourly gives us in Table III 31/4-inches cylinder with 2-inches discharge pipe as proper sizes. If the 10-foot mill is chosen take the 3-inch cylinder. A 14-foot windmill working in a fifteen-mile wind will do more work than two average horses, and when working in a twenty-mile wind will do more work than four good horses, while in a twenty-five mile wind it will do more work than six good horses. Giving the above tables a practical application, a little thought will disclose what a wealth of power stands unappropriated and ready at hand to do many of the drudgeries of work for which large expenditures are annually made. The uses of power windmills are so well understood that it seems out of place to elaborate upon them; the brief space allowed to giving information as to the power of this class of mills when working in different wind velocities, is best expressed in tabular form, Table VI. Fig. 466 represents the working barrel of a deep well pump, such as are used frequently in connection with the larger sizes of aermotors. The tube is usually made of heavy brass—this is drawn so perfectly, as to size and smoothness, that a re-boring is not needed. The plunger is here shown with four cup leather packings, with one ball valve; the bottom valve is also a ball with the seat resting within a conical coupling at the bottom, this with a leather packing makes a water tight joint. Should any accident happen to the bottom valve it may be withdrawn by lowering the sucker-rod until the threaded portion comes in contact with the nut underneath the plunger. By turning the sucker-rod the nut engages the thread on the top of the lower valve-cage. Then by withdrawing the sucker-rod both valves may be drawn up for examination or repairs. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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