Online Encyclopedia
Search over 40,000 articles from the original, classic Encyclopedia Britannica, 11th Edition.
WATER MOTORS
Online EncyclopediaEncyclopedia Home :: VIR-WAT
del.icio.us it!
|
See also:WATER See also:MOTORS . The subject of See also:hydraulic transmission of See also:power is treated generally under POWER TRANSMISSION (Hydraulic), and the See also:present See also:article is confined to water motors. Hydraulic Lifts.—The See also:direct-acting lift is perhaps the simplest of all See also:machines using pressure-water, but as the height of the lift increases, certain problems in construction become exceedingly difficult to See also:cope with, notably those due to the See also:great increase in the See also:weight and displacement of the See also:ram. In fact, with a See also:simple ram it is not possible to lift beyond a certain height with a given pressure and load. It becomes, therefore, necessary to See also:balance in some way the varying displacement of the ram if See also:economy is to be secured in the working: this is often done by the use of See also:counter-weights attached to chains travelling over See also:head sheaves, but this largely destroys the simplicity and safety of the direct-acting lift, and hence some See also:form of hydraulic balancing is more satisfactory and more certain. In one form, shown in fig. 1, the lift See also:cylinder is in hydraulic connexion with a pair of See also:short cylinders placed one above the other, the pistons working in them being connected together by a See also:common See also:rod. Below the See also:piston of the upper cylinder is an See also:annular space E (surrounding the common piston rod) with a capacity equal to the maximum displacement of the lift-ram, while the corresponding annular See also:area C of the piston of the See also:lower cylinder is just large enough when subjected to the working water pressure to enable the See also:work of lifting the See also:net load to be done and any See also:friction to be overcome. The area B of the See also:top See also:side of the upper piston is proportioned in such a way that when under the full water pressure the dead weight of the ram and cage is just balanced when the former is at the bottom of its stroke. With this arrangement the lift - ram and the two balance pistons are always in See also:equilibrium, or, in other words, the ever-changing displacement of the lift-ram is automatically in balance. To work the lift, pressure-water is admitted to the annular space C above the lower of the two balance pistons (the space B above the upper one is always in communication with the pressure-water), and the combined pressure on the two pis-tons is sufficient to lift the cage, ram and load. As the ram ascends it apparently increases in weight, but this is balanced by the greater pressure on the two balance pistons as they descend, owing to the in-crease of the head of water acting on them. To allow the lift-ram to descend, the pressure-water in C above the lower balance piston is discharged through the exhaust into the drain, while that above the upper piston is simply pushed back into the pressure See also:main. As an See also:illustration of the economy of this See also:system, it may be. mentioned that in one lift having a 6-in. ram with a lift of 90 ft., the working load being I ton and the maximum working See also:speed 18o•ft. a See also:minute, the quantity of pressure-water used per See also:journey of 90 ft. was reduced from 109 to 24i gallons by the use of this method of balancing. In another system of hydraulic balance (fig. 2) the ram A has an annular area so proportioned that when it is connected with the water in an elevated tank (usually placed somewhere in the roof of the See also:building), the hydraulic pressure upon it just balances the weight of the ram and cage. Here again, since the Intensity of the pressure on A becomes greater as it descends owing to the increased head, the apparent increase of weight of the lift-ram as it rises is automatically balanced ; water from the high-pressure system is admitted down the hollow ram B and does the work of lifting the live load. Since the introduction of deep-level electric See also:railways in Londonand elsewhere, hydraulic passenger lifts on a large See also:scale have See also:beer brought into use for conveying passengers up and down from the See also:street level to the underground stations. Direct-acting Water Motors.—Owing to the difficulty of securing a durable motor with a simple and trustworthy means of automatically regulating the quantity of water used to the power needed at various times from the motor, not much advance has been recently made in the use of water motors with reciprocating rams or pistons. Probably the most successful one has been a rotary See also:engine invented by Mr See also:Arthur See also:Rigg.' In this engine the stroke, and therefore the amount of water used, can be varied either by See also:hand or by a See also:governor while it is See also:running; the speed can also be varied, very high rates, as much as 60o revolutions a minute, being attain-able without the question of See also:shock or vibration becoming troublesome. The cylinders are See also:cast in one piece with a circular See also:valve, and rotate about a main See also:stud S (fig. 3), while their plungers are connected to a disk See also:crank which rotates above the point 0, which is the centre of the main crank; 0 S being the crank length or See also:half stroke of the engine, any variation in its length will vary the power of the engine and at the same See also:time the quantity of water used. The See also:movement of S is obtained by means of a relay engine, in which there are two rams of different diameters; a See also:constant pressure is always acting on the smaller of these when the motor is at work, while the governor (or hand-power if desired) admits or exhausts pressure-water from the See also:face of the other, and the movements to and fro thus given to the two rams alter the position of the stud S, and thus See also:change the stroke of the plungers of the main engine. Fig. 4 gives an outside view of a 3o-H.P. engine capable of using water at a pressure of 700 lb per sq. in.; the governor is carried within the See also:driving See also:pulley shown at the right-hand end, while the working revolving cylinders are carried insic'e the boxed-in flywheel at the See also:left-hand end, the relay cylinder and its attachments being fixed to the See also:bed-See also:plate in front of the flywheel. On a test one of these engines gave an efficiency or See also:duty of 8o %. Water Wheels.—The Pelton water See also:wheel (fig. 5) has proved a most successful motor when very high heads are available, heads of 2000 feet having been used occasionally. Such machines have been extensively em-ployed in See also:America, and have also lately been used in Great See also:Britain, worked by the FIG. 2.-Hydraulic high-pressure water supplied in large towns. Balancing. The wheel carries a See also:series of cups placed at equal distances around the circumference. A See also:jet or jets of water impinge on the cups, the interiors of which are shaped in such a way that the jet is discharged parallel to its See also:original direction. If the linear velocity of the cups in feet a second is V,, and the linear velocity of the jet is V2, then the velocity of the jet relative to the See also:cup is V2—VI feet a second, and if the whole See also:energy of the water is to be given up to the cups, the water must leave the cup with zero See also:absolute velocity. But its velocity relative to the cup, as it passes back-wards, is —(V2--VI), and since the forward velocity of the cup is V1, the absolute velocity of the water is —(V2-V1)+V1or2V1-V2. This will become zero if VI is 1V2, that is, if the linear velocity of the cup-centres is one-half that of the jet of water impinging upon them. The theoretical efficiency of the wheel FIG. 3.—See also:Section of Rigg's Water- would then be Too %. The Engine. actual efficiency of these wheels when used with high falls is from 8o to 86 %; when used in connexion with high-pressure water in See also:London an efficiency This engine was fully described in See also:Engineering, vol. xlv, n. 61. of 70% has been obtained, and when a See also:dynamo is driven directly by them about 66 % of the hydraulic energy has been converted into electric energy. Pelton wheels are very sensitive to variation of load, and considerable trouble was experienced at first in securing adequate governing when they were used to generate electric energy; but this difficulty has been overcome, and they have been rendered most efficient machines for use with high falls, where See also:ordinary turbines would be difficult to See also:manage owing to the excessive speed at which they would run. In a small See also:installation in the See also:United States water is brought in a 36-in. See also:pipe a distance of 1800 ft., and supplies six Pelton wheels each 28 in. in See also:diameter, running at 135 revolutions a minute under a head of 130 ft. The See also:total power See also:developed is 600 H.P., and though the load See also:factor varies very greatly in this See also:case, the See also:differential type of governor used secures perfect See also:control of the running of the wheels. Turbines.—The tu• rbine has now become one of See also:prime See also:movers employed by See also:man, and in the United States of America and on the See also:continent of See also:Europe 2 its use has enormously increased of See also:recent years. Though no See also:radical changes have been made in the See also:design of turbines for some years, an immense amount of skill and ingenuity has been shown in perfecting and improving details, and such machines of great See also:size and power are now constantly being made, and give every See also:satisfaction when in use. In the " See also:Hercules " See also:turbine, shown in fig. 6, the flow is what is called mixed, that is, it is partly a radial inward and partly an axial flow See also:machine. On entering, the water flows at first in a radial direction, and then gradually, as it passes through the wheel, it receives a downward component which becomes more and more important. See also:Professor Thurston has published the results of a test 1 This and some of the other drawings have been taken from See also:Blaine's Hydraulic Machinery. 2 The following See also:statistics of turbine construction in See also:Switzerland are taken from Schweizerische Bauzeitung (1901), p. 128, which, in the same See also:volume at p. 53, contains a valuable article on the most ;mportant improvements in turbines and their regulation shown n the See also:Paris See also:Exhibition of 1901 :of one of these, which gave an efficiency of 87 % at full load and 70%a at about three-fifths full load. See also:Period. Number Total H.P. See also:Average of H.P. Turbines. 1844–1869 767 36,894 48 1869–1879 1006 66,688 661 1879–1889 1840 133,579 721 1889–1899 2231 400 474 1791 Totals . 5844 637,635 Another turbine of the mixed flow type is the " See also:Victor," which consists of three parts—the See also:outer See also:guide case, and, inside this, the I See also:register See also:gate, and the wheel. The gate regulates the speed of the wheel by varying the quantity of water; when fully open it merely forms a continuation of the guide passages, and thus offers no obstruction to the flow of the water, but by giving it a movement through a See also:part of a revolution the passages are partly blocked and the flow of the water is checked. This form of regulation is fairly efficient down. to three-See also:quarter opening. Turbines of this type may also be used on See also:horizontal shafts, and are very useful in the case of See also:low falls where there is a large amount of water and the head is fairly constant. At See also:Massena, in New See also:York See also:State, 75i000 H.P. is to be developed from fifteen sets of these turbines working under a head of 40 ft. Each generator can develop 5000 H.P. at a potential of 2200 volts, and is driven by three horizontal See also:double turbines on the same See also:shaft; when working under a minimum head of 32 ft. at 150 revolutions, each turbine will have a nominal See also:horse-power of See also:I000. Probably the most important application of turbines to the See also:generation of power on a great scale is that at See also:Niagara Falls. The water is tapped off from the See also:river Niagara about i m. above the falls and brought by a See also:canal to the power- See also:house. The wheel-See also:pit is 18o ft. in See also:depth, and is connected with the river below the falls by a tail-See also:race, consisting of a See also:tunnel 21 ft. high and 18 ft. Io in. wide at its largest section. The original turbines were of the " Fourneyron " type, and a See also:pal: were mounted on each See also:vertical shaft, the two being capable of giving out 5000 H.P. with a fall of 136 ft. Each pair of wheels is built in three storeys, and the outflow of the water is controlled by a cylindrical gate or sluice, which is moved up and down by the See also:action of the governor. As the pair of wheels and the big vertical shaft (which is of hollow See also:steel 38 in. in diameter) with the revolving part of the dynamo mounted on the upper end of the shaft weigh about 152,000 ib, a See also:special See also:device, since adopted in other similar power See also:plants, was designed to balance in part this dead weight. The water passes from the penstock through the guide See also:blades of the upper wheel, and in doing so acts in an upward direction on a See also:cover of the upper wheel, which thus becomes, as it were, a balance-piston. The total upward pressure on this piston is calculated to be equal to 150,000 lb; hence the shaft-See also:bearings are practically relieved from p_*essure when the wheels are running. Another turbine which has come into extensive use is the " See also:Francis, ' an exceedingly efficient turbine on a low fall with large quantities of water. At See also:Schaffhausen two of them with a fall of 121 ft. de« veloped 430 H.P., when the older turbines only gave 26o H.P., the efficiency of the Francis turbine being in this case 86 % at full load and 77% at half load. A recent form of the Jonval turbine is shown in fig. 7. This turbine was designed to give 1250 H.P. with a fall of 25 ft. and an efficiency of 77 %. It is fitted with a suction pipe and a circular balanced sluice for admitting and cutting off the water-See also:supply. The wheel is 12 ft. 31 in. in diameter, and has a speed of fifty revolutions per minute, and the power generated is transmitted through See also:bevel-gearing to a horizontal shaft from which the power is taken III~I_li Ilia ll~„IH! 1fl off for various purposes. When See also:complete the turbine weighed about 140 tons. There is a regulating arrangement, by which one-half of the guide-passages can be shut off in pairs from the water, and at the same time See also:air is freely admitted into these unused passages by pipes which pass through the hinges of the controlling shutter. Tests of a turbine of this slow-moving type showed an effciency of 82 % at full gate, and one of 75 % when half of the passages in the guide-blades were closed by the shutters, as described above. As an illustration of the use of water-power, even at a considerable distance from a See also:town, the case of See also:Lausanne may be described. The town has secured the right of using a See also:waterfall of 113 to 118 ft. high, by impounding the Rhtnenear See also:Saint See also:Maurice. In dry seasons this will supply 6000 H.P., and for quite ten months in an ordinary See also:year 14,000 H.P. The plant in 1902. consisted of five turbines, having horizontal axles, and each developing moo H.P. when running at 300 revolutions a minute. They drive electric generators, and the current so produced is taken at a pressure of 22,000 volts on overhead wires a distance of 35 M. to Lausanne, the loss being estimated not to exceed to% in the See also:long transmission. Near the town is a station for reducing the voltage, and current is distributed at 125 volts for See also:lighting purposes and at 50o volts for use on the tramways and for other power purposes. AuTxoRITIEs.—For further See also:information concerning the construction and employment of water motors, the reader is referred to the following papers and textbooks:—Prot. Inst. Mech. Eng. (1882), p.119 (1889), p. 350; (1895), p. 353. (These papers contain full accounts of recent forms of lifts—Engineering, vol. lxvii. pp. 91, 128, 16o, " Power Station at Niagara ' ; vol. lxxii. pp. 391-767, " Governing of Water Wheels."—Prot. Inst. See also:Civil Eng., vol. lxxxvi. p. 6o, " See also:Mersey Railway Lifts "; vol. xciii. p. 596, " Experiments on Jonval and See also:Girard Turbines at Alching "; vol. xcvi. p. 182, " Hydraulic Canal Lifts "; vol. cii. p. 154, " See also:Keswick Water-Power Electric Station "; vol. cxii. p. 410, ` Hydraulic See also:Works at Niagara "; vol. cxviii. p. 537, " A 12-Mile Transmission of Power Generated by Pelton Wheels "; vol. cxxiii. p. 530, " The Pelton Water Wheel "; vol. cxxiv. p. 223, " The Niagara Power Works "; vol. cxxvi. p. 494, " The Rheinfelden Power Transmission Plant "; vol. cxli. E. " Electric Transmission Plants in See also:Transvaal," p. 307, " Turines "; vol. cxlii. p. 451, " See also:Electrical Installations at Lausanne "; vol. cxly. p. 423, " Water Power at Massena "; vol. cxlvii. p. 467, " Some Large Turbine Installations."—See also:Wood, Theory of Turbines; Bovey, See also:Hydraulics; Bjorling, Hydraulic Motors; Blaine, Hydraulic Machinery; See also:Bodmer, Hydraulic Motors; Unwin, " Water Motors " (Lectures on Hydro-See also:Mechanics, Inst. Civil Eng., 1885). (T. H. B.)
WATER-See also:OPOSSUM, or YAP0cK (Chironectes minimus), the single representative of the genus. This See also:animal is distinguished from other opossums by its webbed See also:hind-feet, non-tuberculated soles, and See also:peculiar coloration. Its ground See also:colour is See also:light See also:grey, with four or five sharply contrasted See also: Additional information and CommentsThere are no comments yet for this article.
» Add information or comments to this article.
Please link directly to this article:
Highlight the code below, right click, and select "copy." Then paste it into your website, email, or other HTML. Site content, images, and layout Copyright © 2006 - Net Industries, worldwide. |
|
|
[back] WATER |
[next] WATER POLO |