Hydraulic machinery may be broadly divided into Water motors may be divided into In hydraulic motor machines a quantity of water descending from a higher to a lower level, or from a higher to a lower pressure, drives a machine which receives energy from the water and applies it to overcoming the resistances of other machines doing work. In the next general class, work done on the machine by a steam engine or other source of energy is employed in lifting water from a lower to a higher level. A few machines such as the ram and jet pump combine the functions of both motors and pumps. The subject of water wheels is but a continuation of much that has been illustrated and defined in the historical introduction to which is now added the following summary. In every system of machinery deriving energy from a natural water-fall there exist the following parts: (1) A supply channel, leading the water from the highest accessible level, to the site of the machine; this may be an open channel of earth, masonry, or wood, or it may be a closed cast or wrought-iron pipe; in some cases part of the head race is an open channel, part a closed pipe. (2) Leading from the motor there is a tail race, culvert, or discharge pipe delivering the water after it has done its work. (3) A waste channel placed on or at the origin of the head race by which surplus water, in floods, escapes. (4) The motor itself, which either overcomes a useful resistance directly, as in the case of a ram acting on a lift or The great convenience and simplicity of water motors has led to their adoption in certain cases, where no natural source of water power is available. In these cases, an artificial source of water power is created by using a steam engine to pump water to a reservoir at a great elevation, or to pump water into a closed reservoir in which there is great pressure. Water flowing from the reservoir through hydraulic engines gives back the energy expended, less so much as has been wasted in friction. Where a continuously acting steam engine stores up energy by pumping the water, while the work done by the hydraulic engines is done intermittently,—this arrangement is considered the most useful. Note.—“Wherever a stream flows from a higher to a lower level it is possible to erect a water motor. The amount of power obtainable depends on the available head and the supply of water. In choosing a site the engineer will select a portion of the stream where there is an abrupt natural fall, or at least a considerable slope of the bed. He will have regard to the facility of constructing the channels which are to convey the water, and will take advantage of any bend in the river which enables him to shorten them. He will have accurate measurements made of the quantity of water flowing in the stream, and he will endeavor to ascertain the average quantity available throughout the year, the minimum quantity in dry seasons, and the maximum for which bye-wash channels must be provided. In many cases the natural fall can be increased by a dam or weir thrown across the stream. The engineer will also examine to what extent the head may vary in different seasons, and whether it is necessary to sacrifice part of the fall and give a steep slope to the tail race to prevent the motor being flooded by backwater in freshet time. In designing or selecting a water motor it is sufficient to consider only its efficiency in normal working conditions. It is generally quite as important to know how it will act with a scanty water supply or a diminished head. The greatest difference in water motors is in their adaptability to varying working conditions.”—Encyc. Brit. Fig. 110. Water wheels are large vertical wheels driven by water falling from a higher to a lower level: they are motors on which the water acts, partly by weight, partly by impulse. Turbines are wheels, generally of small size compared with water wheels, driven chiefly by the impulse of the water. Before entering the moving part of the turbine, the water is allowed to acquire a considerable velocity; during its action on the wheel this velocity is diminished, and the impulse due to the change of momentum drives the turbine. Roughly speaking, the fluid acts in a water-pressure engine directly by its pressure, in a water wheel chiefly by its weight causing a pressure. A flutter-wheel is shown in Fig. 110. This is a water wheel of moderate diameter placed at the bottom of a chute so as to receive the impact of the head of water in the chute and penstock. Its name is derived from its rapid motion, the effect of which is to cause a commotion of the water like “the fluttering” of a fowl. Impact Wheels.—The simplest and most imperfect of the horizontal wheels are the so-called impact wheels or impact turbines, such as shown in Fig. 111. Fig. 111. They consist of 16 or 20 rectangular blades fastened to the wheel at an inclination of 50° to 70° with the horizon. The water is brought on through a race of 40° to 20° inclination, so that it strikes at about right angles upon the blades. These wheels are used in falls from 10 to 20 ft., where a large number of revolutions is necessary, as in grain mills, where the moving millstone is hung on the vertical shaft of the wheel, hence intermediate gearing is unnecessary. These crude machines are found in Southern Europe, North Africa, in the Alps, Pyrenees, and in Algiers. They are about 5 ft. in diameter, and the blades are 15 inches high and 8 to 10 inches long (measured radially). Fig. 112. Fig. 112 shows an “undershot water wheel.” In this style of wheel, the work is done by impact alone, as the running water acts only on a few immersed buckets on the under side of the wheel. In the breast wheel, Fig. 113, the water is admitted on a level or slightly above the center of the shaft, so that the water acts by impact and weight. Fig. 113. Note.—“A weir is a dam erected across a river to stop and raise the water, as for the purpose of taking fish, of conveying a stream to a mill, of maintaining the water at a level required for navigating it, or for the purposes of irrigation.” For facilitating the computation of the quantity of water flowing over weirs, Weir Tables, are used, based upon approved formulas, of which “Francis’ Formula” is perhaps the most reliable. These tables are applicable to the subject of water wheels but cannot be printed in this work. Fig. 114. Fig 114 represents an over-shot water wheel (F G H L, with axis at O) in which the water flows upon the top of the wheel at h, in the same direction in which it revolves, therefore the impact of the water is utilized upon the upper buckets H, a, b, after which the weight of the water acts in the buckets c, d, e, F, e´, d´ and c´. At b´ the buckets begin to overflow and empty themselves as shown at a´. It will be seen that the water acts upon almost one-half the circumference of this wheel, thus realizing the greatest mechanical effect with the smallest quantity of water. The current-wheel is perhaps the first application of the force of water in motion, to drive machinery. In the first century B.C., water-wheels for driving mills were used in Asia Minor and on the Tiber. In the former case we suppose, but in the latter case we know, that these were current-wheels. Fig. 115. The tide or current wheel, (Fig. 115) erected in the vicinity of the north end of London Bridge, and subsequently under its During the seventeenth and eighteenth centuries the works were extended from time to time, and occupied one after another of the arches. In the first arch of the bridge was one wheel working sixteen force-pumps. In the third arch were three wheels, working fifty-two pumps. The united effect was 2,052 gallons per minute, raised 120 feet high. In 1767 Smeaton added wheels in the fifth arch. Steam-engines were added about this time to assist at low water and at neap-tides. Thus the matter remained till 1821. Stow, the antiquarian and historian, describes the works in 1600; and Beighton in 1731 gives an account of them at that date. The water-wheels at that time were placed under several of the arches. The axis of these wheels was 19 feet long 3 feet diameter. The radial arms supported the rings and twenty-six floats, 14 feet long by 18 inches wide. The axis turned on brass gudgeons supported by counterpoised levers, which permitted the vertical adjustment of the wheel as the tide rose and fell. On the axis of the wheel was a cog-wheel 8 feet in diameter and having forty-four cogs; meshing into a trundle-wheel 41/2 feet in diameter and having 20 rounds, or pins and whose iron axle revolved in brasses. The axis of the trundle was prolonged at each end, and had quadruple cranks which connected by rods to the ends of four walking beams 24 feet long, whose other ends worked the piston-rods of the pumps. The axis of oscillation of the lever supporting the wheel, and by which it was adjusted to the height of the tide, was coincident with the axis of the trundle, so that the latter engaged the 8-feet cog-wheel in all conditions of vertical adjustment. Cranks operated one end of the beams while pumps were attached to the other end. Fig. 116. Fig. 116 exhibits an overshot water wheel employed at Laxey, Isle of Man, for driving the pumps which drain the mines at that village; these have an extreme depth of 1,380 feet. The wheel is 72 feet 6 inches in diameter, 6 feet in breadth, exerts a force of about 200 horse-power and is capable of pumping 250 gallons per min. from a depth of 1,200 feet. Its crank-stroke is 10 feet. The water for driving it is conducted by pipes from a reservoir on a neighboring hill, and ascends in the column of masonry shown to the left of the wheel. (Knight Vol. III.) An extra crank appears to be shown in the foreground of this reproduction of an old drawing. TURBINE WATER WHEELS.The word turbine is derived from the Latin, “turbo”—that which spins or whirls around—a whirlwind. Fig. 117. The turbine is a horizontal water wheel, and is similar to the hydraulic tourniquet or reaction wheel shown in Fig. 117. This consists of a glass vessel, M, containing water and capable of moving about its vertical axis. At the lower part there is a tube, C, bent horizontally in opposite direction at the two ends. If the vessel were full of water and the tubes closed, the pressure of the sides of C would balance each other, being equal and acting in contrary direction: but, being open, the water runs out and the pressure is not exerted on the open part but only on the opposite side, as shown in the figure A. And this pressure, not being neutralized by an opposite pressure, imparts a rotary motion in the direction of the arrow, the velocity of which increases with the height of the liquid and the size of the aperture. This description and the illustration gives an idea of the crude reaction wheel invented by Barker about 1740; again a turbine is simply a centrifugal pump reversed, but the turbine is usually furnished with curved guide vanes to guide the water as it enters the wheel. Note.—The steam turbine has come into common use and competes in its economical performance with the simpler and less economical types of the steam engine; it is impelled by steam jets, the steam impinging upon vanes or buckets on the circumference of a rotating disc or cylinder. In those turbines which are without guide blades—i. e., which have a high fall—the discharged water still possesses a great velocity and the wheel is thereby deprived of a considerable part of mechanical power. This loss can, however, be obviated or lessened by using the energy of this discharged water to drive a second wheel. A construction of this sort has been carried out by Ober-Bergrath Althaus in the tanning mill at Vallendar near Ehrenbreitstein. The essential parts of the arrangement can be seen in Fig. 118. A E A is an ordinary reaction wheel with four curved revolving pipes and a fall of 124 ft., and B B is a larger wheel with floats which is set in rotation by the water issuing from A. A. Since the two wheels turn in opposite directions, they must be connected together by a special form of wheel-work. The outer wheel affords the additional advantage of serving at the same time as a fly-wheel, thereby giving a more uniform rate of motion to the whole machinery. Fig. 118. Turbines are variously constructed, but all have curved floats or buckets against which the water acts by its impulse or reaction in flowing either outward from a 1 central chamber, 2 inward from an external casing, 3 from above downward, and, 4 from below; these constructions are either divided into outward, vertical or central discharge wheels. Turbines may also be divided into reaction turbines, or those actuated substantially by the water passing through them (their buckets moving in a direction opposite to that of the flow); impulse turbines or those principally driven by impact against their blades or buckets (the buckets moving with the flow); and combined reaction and impulse wheels which include the best modern types of turbines. In reaction turbines the Fig. 119. Turbines in which the water flows in a direction parallel to the axis are called parallel flow turbines—or journal turbines. The turbine-dynamometer is a device used for measurings or testing the power delivered by turbines (whence its name). Fourneyron’s Turbine. This is, in its latest form, when properly constructed, the nearest perfect of the horizontal water-wheels. It revolves either in the air or under water, and may be either high or low pressure. For the low-pressure wheel, the water enters the flume from the open reservoir, with free surface, as in Fig. 119. For high pressure, the reservoir is boxed up and the water brought in at the side through a pipe, as shown in Fig. 124, page 136. The first is for low and the second for high falls. Note.—The early history of the turbine is one of considerable interest especially in view of the development of the steam, from the water turbine. “M. Fourneyron, who began his experiments in 1823, erected his first turbine in 1827, at Pont sur l’Ognon, in France. The result far exceeded his expectations, but he had much prejudice to contend with, and it was not until 1834 that he constructed another, in Franche ComtÉ at the iron-works of M. Caron, to blow a furnace. It was of 7 or 8 horse-power, and worked at times with a fall of only 9 inches. Its performance was so satisfactory that the same proprietor had afterwards another of 50 horse-power erected, to replace 2 water-wheels, which together, were equal to 30 horse-power. The fall of water was 4 feet 3 inches, and the useful effect, varied with the head and the immersion of the turbine, 65 to 80 per cent. Several others were now erected: 2 for falls of seven feet; 1 at Inval, near Gisors, for a fall of 6 feet 6 inches, the power being nearly 40-horse, on the river EptÉ, expending 35 cubic feet of water per second, the useful effect being 71 per cent. of the force employed.” Fig. 120. The Leffel-Samson turbine wheel is shown in the engraving, Fig. 120, page 129, where N.N. represents the bottom casting of the case flanged to support the wheel by resting upon the bottom of the penstock. The draft tube I is of conical shape as represented at J. J. to reduce the friction of discharge water which after performing its work in the wheel escapes at the bottom of the draft tube. This tube must always project into the tail water at least two or three inches. The gates H.H.H. are pivoted at the center so that they are balanced and are opened and closed with the least possible friction. These gates are operated by rods L. L., connecting with a rack and pinion which are manipulated by the operator as occasion requires, by an extension shaft from the coupling K, having a hand-wheel on top. Fig. 121. Power is transmitted from the wheel shaft F to the gears and pulleys connected with the coupling above; the manner of setting turbine wheels in openstocks is shown a few pages further on. From the construction of gates and guides upon turbine wheels one may readily see the absolute necessity of carefully guarding the flume against the admission of sticks and other solid materials that might wreck the wheel or jam the gates so that they could not be operated; this is best accomplished by placing a water rack in front of the head gate at the entrance to the flume. These water racks are best made of flat bars of wrought iron placed edgewise in a vertical position, or what is better, let the top incline say one foot or two (depending upon the size of flume) towards the head gates. When placed in an inclined position it is very much easier to clean the rack from drift wood and the like than when placed in a vertical position as by means of a hoe or scraper these obstructions may be hauled up over the top of the inclined rack. The racks should be made very strong and substantial to guard against being broken by ice in the winter, for should the rack give way at any inopportune time the admission of sticks and other rubbish might wreck the wheel. The “runner” which is the revolving part, as shown in Fig. 121, is composed of two separate and distinct types of wheels, and has two diameters, as shown. Each wheel or set of buckets receives its separate quantity of water from one and the same set of guides but each set acts only once and independently upon the water used, hence the water does not act twice upon the combined wheel as might be supposed, as in the compound steam engine. The upper wheel G receives the water as shown by the arrows at A, and has a central and downward discharge, while the lower wheel C receives the water as shown by the arrows at B and has an inward, downward and outward discharge as shown by the arrows at D. These two sets of buckets need to be exceedingly strong. The lower set B are made of heavy flanged steel plate and are cast into their places by being placed in the sand mould, and the cast iron flows around them forming the heavy ring C, surrounding the outer and lower edges. This ring is a part of the diaphragm which separates the two wheels. The upper edge of the ring C is beveled to form a neat joint which prevents any unnecessary loss of water. This runner is balanced and secured to a hammered iron or steel shaft F. It is supported usually by a step of the best specially selected hard wood thoroughly soaked in oil for months before use. The lower end of the shaft is dished out at E, forming a true arc of a circle—concave—while the wooden step is made spherical—convex—to fit into the end of the shaft. The step is formed in this way so that no sand can lodge between the bearing surfaces, and cut them out. The resident oil in the wood combined with the water make a most durable means of lubrication, and these steps last for many months where the water is clear. Fig. 122. To get at the exact quantity of water consumed by a turbine wheel, one cannot make an accurate calculation from the openings through the wheels but the water is measured after it These wheels are made either for vertical or horizontal shafts and are also made single or double. The engraving, Fig. 122, shows a Hercules turbine within the case and gate ready to set in the penstock. Up to the year 1876 this make of wheel tested at the flume of the Holyoke Water Works showed the highest efficiency at all stages of gate, namely 87 per cent. (page 97, Emerson’s tests). The design of case will naturally lead the reader to conclude that this wheel has, 1, an inward, 2, downward and, 3, an outward discharge which is correct. The gate is simply a curb or hollow cylinder which forms a sleeve outside the case and is raised and lowered by the gearing and rack shewn in the engraving. As this sleeve rises it gradually uncovers the openings shown which admits water into the wheel. Horizontal Turbine—The turbine of 10,500 horse power installed in the Shawinigan plant, Canada, see IV Pt. 2. is of the horizontal type, the water entering at, A, the lowest part of the turbine and flows around and fills the outer special tube, passes through an annular gate, flows radially through the wheel thence out through two draft tubes, B, one on each side. The weight of the water wheel is 182 tons, the shaft weighing 10 tons and the bronze runner 5 tons. It is 30 feet from base to top and 32 feet 21/2 inches wide over all. The shaft, C, is of solid forged steel, 22 inches diameter in the middle, tapering down to 10 inches diameter on one end and 16 inches diameter on the other, the distance between bearings being 27 feet. The intake is 10 feet in diameter and the quantity of water going through the turbine when developing full power is 395,000 gallons a minute. The speed of the wheel is 180 revolutions per minute with a head of water acting on the turbine of 125 to 135 feet. Fig 123 is designed to show The Setting of a turbine wheel in a wooden penstock. Fig. 123. The principal and most essential dimensions necessary to be considered in setting turbines are indicated by letters, each size having its own particular dimensions. In setting the wheel in the ordinary penstock it is necessary in the first place, to have the floor exactly level, and it is generally more convenient to lay down a ring of soft wood around the If the wheel is a large one and was taken apart for shipment, the draft tube is first erected in position, then the wheel is placed on its step, the other parts being put on in their order. The step and other bearings are adjusted before leaving the shop, but it will sometimes happen that they will in some way get shifted, and as the wheel is being put together, they should be inspected and readjusted, if necessary. The only change that can occur in the step is its vertical adjustment, which is regulated by screws. When the right height is found, the broad flange around the lower part of the wheel should stand about one-sixteenth of an inch below the under side of the base of the guide rim where it rests upon the draft tube. The adjustable bearing on the top of the cover plate should be fitted up closely around the shaft, but not screwed so tightly as to bind it. All these wheels above fifteen inches in diameter are provided with chains and weights to counterbalance the weight of the gate, so that it will move easily. It is best, when it can be done without much trouble, to carry the weights outside of the flume, but they can be used inside where the height is sufficient, although it will require a little more weight to be as effective. When the wheel is not likely to be started up at once, it is a good plan, when putting it together, to smear the step and the shaft at the bearing with tallow, as a protection against rust while it remains idle. It is sometimes necessary to use a draft tube longer than is ordinarily attached to the wheel. If properly constructed and applied there will be no sensible loss of power, but it must be air tight, and when of considerable length it is better enlarged gradually toward the lower end, especially in cases where it may be necessary to carry this tube near the pit bottom. Iron cases for Turbines. Fig. 124 shows the setting of a Hercules wheel within an iron case. Fig 124. Although the expense of iron is as a rule considerably greater than wood, the results obtained by the use of iron It is generally conceded that there is a great risk of the step becoming heated and burning out when placed in a draft tube above the tail-water, and a jet of water is required to counteract this tendency to overheat. As all such fixtures are liable to derangement and often fail to operate, we are in favor of setting the wheel with the step immersed, whenever it can be done without too great expense. This case consists of two cast iron heads with boiler iron sides and is provided with a cover, so that the wheel may be taken out entire. This cover is fitted with stuffing boxes for both wheel and gate shafts, and a manhole affords easy access to the wheel. The bearing surfaces of the heads are nicely turned, insuring tight joints, and all holes for rivets are accurately spaced and drilled. The heads of the larger cases are made to clamp, the two halves being planed together; the cases are fitted with mouthpieces having cast iron flanges for feeder connections, to secure by bolts to either iron or wooden feeders. Where two wheels of the same or different diameters are to be used, corresponding cases connected in the centre with one common feeder connection, or are placed in cases provided with separate feeders. In connection with these cases an iron draft tube of any desired length may be used. The wheel is usually fitted to the case before leaving the works, and in erecting the smaller wheels, all that remains to be done is to set the case on the foundations provided for it and make the necessary connections as stated in explanation previously made for Figs. 122 and 123. The general arrangements required for the proper erection of turbines are well understood by competent millwrights and do not in ordinary cases present any serious difficulties. It may be of interest to many, and to the advantage of some who In practice there is almost always a little loss of head due to the velocity with which the water passes through the channels leading to and away from the wheel, and it should be the aim in constructing flumes to bring the loss to a minimum. When the size of the wheel and the quantity of water to be used have been determined, 1, the size of the conduit for carrying the water to the wheel, 2, the width and depth of the wheel-pit and tail-race, and 3, the dimensions and location of the flume for the wheel are to be considered and properly arranged. All of these should be of such dimensions as to insure the flow of water through them at a moderate velocity, and with as little change of direction as may be practicable. The larger the pipe or canal the better, but there must be a limit in practice, and it may be laid down as a general rule that a velocity of three feet per second is good practice in short tubes of uniform section of not more than fifty feet in length; but the velocity should be reduced as the distance increases, until in a length of 200 feet, it should not exceed two feet per second. The same rule applies to the tail-race, except that the velocity should be somewhat lower in ditches cut through rock or earth and having the naturally resulting roughness of sides and bottom. The width and depth of the pit below the wheel may, for a given wheel, vary somewhat as the water discharged into it is greater or less; therefore, the dimensions should increase with a greater head for the same wheel. The following is an approximate rule for the dimensions of the pit, say for a head of twenty feet: width of pit equal to four times the diameter of wheel, depth below the level of tail-water one and a half times the diameter of wheel. The flume for the wheel should be about three times the diameter of the wheel in its width or diameter, and if it is decked over at the top it should be high enough inside to clear the coupling on the wheel shaft. The Watertight Turbine is a special machine designed to keep the case tight by the pressure of the water against the gates at the sides, no matter how much these gates wear. Fig. 125 shows the plan of chutes, gate-seats, gates, and buckets of the wheel. Part of the gates are shown open, and others are closed. The gates make a quarter of a turn in opening, and the same in shutting, and to open all the gates, the gate wheel makes half a revolution. The upper half of case shows the gate-wheel and pinion for operating its parts. Fig. 125. The small illustration is a perspective view of the gate and gate segment used on the watertight turbine. The part cut away forms part of the chute when the gate is open as shown in the lower left-hand side of the figure. The sharp edge of the gate cuts off sticks and rubbish which are liable to get in the wheel, which is an obvious advantage. Another desirable feature claimed for this wheel is the plan of operating the gates in opposite pairs; by this means 2, 4, 6, 8 or 10 full gates may be opened at will, according to the power required. The Niagara Falls Turbine.—Fig. 126. Turbines at Niagara Falls. A number of turbines installed at Niagara Falls, N. Y., are here briefly described; they are about 5,000 horse-power each; a canal leads water from the river to the wheel pit. The water is carried down the pit through steel penstocks to the turbines, which are placed 136 feet below the water level in the canal. After passing through the wheels the waste water is conveyed to the river below by a tunnel 7,000 feet long. The “plan” Fig. 126 shows a cross-section of the wheel pit, with an end view of a penstock, wheel case and shaft. Fig. 126 exhibits part of a vertical section of the wheel pit and a side view of this penstock, with the enclosing case and shaft of the turbine. Top View or Plan of Fig. 126. This turbine has a rock-surface wheel pit, but this surface is protected by a brick lining having a thickness of about 15 inches. The width of the wheel pit is 20 feet at the top and 16 feet at the bottom, and the cylindrical penstock is 71/2 feet in diameter. The shaft of the turbine is a steel tube 38 inches in diameter, built in three sections, and connected by short In Fig. 126 is shown a vertical section of the lower part of the penstock, shaft, and twin wheels. The water fills the casing around the shaft, passes both upward and downward to the guide passages, through which it enters the two wheels, causes them to revolve, and then drops down to the tail race at the entrance to the tunnel, which carries it away to the river. The gate for regulating the supply is seen upon the outside of these wheels, both at the top and bottom, Fig. 126. Fig. 128 gives a larger vertical section of the lower wheel with the guides, shaft, and connecting members. The guide passages, and the wheel passages, are triple as shown so that the latter may be filled not only at full gate, but also when it is one-third or two-thirds open, thus avoiding the loss of energy due to sudden enlargement of the flowing stream. The two horizontal partitions in the wheel are also advantageous in strengthening it. The inner radius of the wheel is 311/2 inches and the outer radius is 371/2 inches, while the depth is about 12 inches. In this figure the gate is represented closed and to open, it moves downward uncovering the guide passages as shown in Fig. 126, the position it occupies loaded. In Fig. 127 is shown a half-plan of one of the wheels, in a part of which are seen the guides and vanes, there being 36 of the former and 32 of the latter. Although the water on leaving the wheel is discharged into the air, the very small annular space between the guides and vanes, together with the decreasing area between the vanes from the entrance to the exit orifices, ensures that the wheels move like reaction turbines for the three positions of the gates correspond to the three horizontal stages or openings through the guides as shown in Fig. 128, i.e., three stages of gate. Note.—A test of one of these wheels, made in 1895, developed 5,498 electrical horse-power, generated by an expenditure of 447·2 cubic feet of water per second under a head of 135·1 feet. The efficiency of the dynamo being 97 per cent., the efficiency of the wheel and approaches was 821/2 per cent. Fig. 127. The average discharge through one of these twin turbines is about 430 cubic feet per second, and the theoretic power due to this discharge is 6,645 horse-power. Hence if 5,000 horse-power be utilized the efficiency is 75.2 per cent. Under this discharge the mean velocity of water in the penstock is nearly 10 feet per second, but the loss of head due to friction in the penstock will be but a small fraction of a foot. The pressure-head in the wheel case is then practically that due to the actual static head, or closely 1411/2 feet upon the lower and 130 feet upon the upper wheel. The absolute velocity of the water when entering the wheel is about 66 feet per second, so that the pressure-head in the guide passages of the upper wheel is nearly 66 feet. The mean absolute velocity of the water when leaving the wheels is about 19 feet per second, so that the loss due to this is only about 4 per cent. of the total head. Note.—The above description refers to the ten turbines in wheel pit No. 1. The illustrations are those of the wheels called units 1, 2, and 3 which were installed in 1894 and 1895. Units 4 to 10, inclusive, installed in 1898-1900, are of the same type except that both the penstock and wheel case have cast-iron ribs on their sides which rest on massive castings built into the masonry of the side walls. This arrangement dispenses with the supporting girders shown in Fig. 126 and gives much greater rigidity to both penstocks and wheels. Fig. 128.—Enlarged Vertical Section of Lower Wheel, Showing Gates. The weight of the dynamo, shaft, and turbine is balanced, when the wheels are in motion, by the upward pressure of the water in the wheel case on a piston placed above the upper wheel. The upper disc containing the guides is, for this purpose, perforated, so that the water pressure can be equalized. WATER PRESSURE ENGINES.Water pressure engines are machines with a cylinder and piston or ram, in principle identical with the corresponding part of a steam engine; the water is alternately admitted to and discharged from the cylinder, causing a reciprocating action of the piston or ram. It is admitted at a high pressure and after doing its work on the piston is discharged. The water in some of these machines acquires a high velocity; the useful work is due to the difference in the pressure of admission and discharge, whether that pressure is due to the weight of a column of water of more or less considerable height, or is artificially produced. When an incompressible fluid such as water, is used to actuate piston engines, two special difficulties arise. One is that the lost work in friction is very great, if the water attains a considerable velocity; another is that there is over-straining action on the machinery. The violent straining action due to the more or less sudden arrest of the motion of water in machinery is termed hydraulic shock. For these reasons the maximum velocity of flow of water in reciprocating hydraulic machines should generally not exceed 5 to 10 feet per second. Under high pressure, where there is less object in saving and it is very important to keep the dimensions of the machinery small, Mr. Anderson gives 24 feet per second as the limit of velocity. In large water-pressure engines used for pumping mines the average piston speed does not exceed 1/2 to 2 feet per second. The suitability of water for the transmission of power has been fully recognized in recent years; the facility with which water under pressure is capable of being utilized, and the advantages that attend its use in motors have resulted in many practical difficulties being overcome, which were at first considered insurmountable. At the outset of the employment of water pressure it was feared that the water in the pipes and machinery might freeze. This, however, has been found not to be a difficulty where well-known precautions are taken. The working parts should, where possible, be placed under ground, or should be cased in, if they are above ground. The water should be run out of all valves and cylinders which cannot be cased in, and protected as soon as the working of the machine ceases. A very small gas jet or lamp placed near the unprotected parts will prevent freezing. Experiments have also shown that a mixture of glycerine and water prevents the effects of frost at a temperature as low as 16° Fahr., provided the glycerine has a specific gravity of 1.125, and that it is mixed in the proportion of one part of glycerine by weight to four parts of water. Where water is used over again in the machines (by returning the exhaust water from the machines to a reservoir), such addition of glycerine is more easily resorted to. Where moderate risks of frost have to be dealt with, the proportion of one gallon of glycerine to 300 gallons of water proves effectual. If the water is at a high pressure, such as 1,500 lbs. to the square inch, it is less liable to freeze than when used at a low pressure. Again, it was at first feared that accidents might be frequent from the bursting of hydraulic pipes and cylinders under high pressure. Such, however, has been proved not to be the case in practice, and even where pipes or cylinders do burst, the pressure is at once dissipated, as the body of water which can escape at the opening is but slight. It is desirable to use water which is as free as possible either from suspended matter or from chemical impurity. The former increases the wear and tear of the packing, and is otherwise inconvenient, and the latter acts injuriously on the seats and fittings of valves. Sea-water can be used for hydraulic machinery, but on account of its corrosion, fresh-water is better. Water-pressure has sometimes been applied to operate machines which are worked continuously and not intermittently, and to continuous working rotary machines. This is unwise, for in applying hydraulic power to the continuous working of shafting or shop tools, the amount of power developed by the hydraulic engine cannot be varied to suit the work to be done, neither can the speed be regulated with sufficient nicety. Pressure or Hydraulic Motors form an interesting variety of hydraulic devices; they consist of working cylinders with valves and pistons, and resemble forcing pumps in their construction, but differ from them in their operation; the pistons not being moved by any external force applied to them through cranks, levers, etc., but by the weight or pressure of a column of water acting directly upon or against the pistons. Pressure engines or motors are applicable to locations—such as afford a suitable supply of water for the motive column; but where-ever refuse, impure, salt or other water can be obtained from a sufficient elevation, such may be used to raise a quantity of fresh water by these machines. The stress considered in hydro-mechanics is always a pressure, as liquids are in general capable of sustaining only a slight tension without disruption: the intensity of the pressure is measured by the number of units of force per unit of area. Thus we say, one thousand pounds of pressure per square inch of piston—the pounds and the square inches are the units used in these calculations. Figs. 129, 130. The invention of pressure engines brought to light a new mode of employing water as a motive agent: and also the means of applying it in locations where it could not otherwise be used; with pressure engines the motive agent may be taken to the machine itself. In valleys or lowlands, having no natural fall of water, but where that liquid can be conveyed in tubes from a sufficient elevation (no matter how distant the source may be), such water, by these machines, may be made Pressure engines afford an illustration of the variety of purposes to which a piston and cylinder may be applied. These were probably first used in piston bellows; next in the syringe; subsequently in pumps of every variety; and then in water-pressure and steam engines. The moving piston is the nucleus or elemental part that gives efficiency to them all; and the apparatus that surround it in some of them, are but its parts. The history of machines composed of pistons and cylinders also illustrates the process by which some simple inventions have become applied to purposes, foreign to those for which they were originally designed—each application opening the way for a different one. In another form hydraulic motors have been adopted, in favorable locations, as first movers of machinery, and when thus used, they exhibit a very striking resemblance to high pressure steam engines. Indeed, the elemental features of steam and pressure engines are the same, and the modes of employing the motive agents in both are identical—it is the different properties of the agents that induces a slight variation in the machines—one being an elastic fluid, the other a non-elastic liquid. Fig. 131. Fig. 132. In steam engines a piston is alternately pushed forward and back in its cylinder by steam; and by means of the rod to Note.—“The hydraulic engine of Huelgoat, in Brittany, is used to drain a mine; is single-acting, and acts directly to lift the piston of the pump. It makes five and a half strokes per minute, the stroke being a little more than eight feet in length. The piston-rod is 767 feet long, and it weighs 16 tons. The power of the engine is derived from a source at a height 370 feet above its own level.”—Knight. In default of a natural head of sufficient pressure, the head is sometimes established in an accumulator of power; this is a body of water driven into a reservoir under heavy pressure, by forcing pumps worked by power. In cities where the water distribution is from elevated reservoirs, and in which the water supply is sufficiently abundant to justify the application of a portion of it to industrial uses, the water-engine or motor is recommended. The following description of a water engine of world-wide adaptation will, if attentively studied, show the working of an approved type of this machine: Ramsbottom’s hydraulic engine (Figs. 129 and 130), is oscillating, and employs two cylinders b, l, operating one crank-shaft, a, by means of two cranks at right angles to each other. In one of the accompanying figures the channels of induction are marked j and are cast on the cylinders; the dotted circle c shows the position of the supply and discharge pipes; in the other figure these pipes are indicated by arrows. The two views are vertical cross-sections at right angles to each other, one being through the axis of the cylinders and the other through the middle post in which the inner trunnions of the cylinders are journaled. The apertures of induction are seen at h and those of eduction at i, and have the form of truncated circular sectors, whose center is the center of motion. The induction and eduction spaces are divided by a sectoral partition; the apertures of admission and discharge on the sides of the cylinders are of similar construction. The surfaces of contact between the cylinders b, l and the support d are planed and polished and are made water-tight by the adjusting screws m m of the pivots. When the piston p is at the end of its course in either direction the cylinder and crank are vertical, In the next moment the flow of water will recommence, the cylinder discharging itself from the full side of the piston, and filling anew from the opposite side. Air chambers and relief-valves are used as a provision against counter-pressure and hydraulic shocks. The Brotherhood three-cylinder reciprocating engine is an appliance for producing rotary motion by water-pressure. The working parts of the Brotherhood three-cylinder hydraulic engine consist only of the three pistons and connecting rods, one crank and one rotating balanced valve and spindle which fits into the driver and is turned direct from the crank-pin; there are no glands, stuffing boxes, or oscillating joints. It is shown by Figs. 131, 132. The three cylinders, A (made in one casting) are always open at their inner ends, and are attached to a central chamber, B. They contain three pistons, P, which transmit motion to the crank-pin through the rods, C. The water is admitted and exhausted by means of the circular disc valve, V, having a lignum-vitÆ seat. The valve is rotated by the eccentric pin, E. A face view of this valve is shown above the steam chest. It has segmental ports which, in rotating, pass over apertures in the valve seat. There being no dead centers, the engine will start from all positions of the crank-pin, and a uniform motion of the shaft is produced without a flywheel. The pressure is always on the outer end of the piston, so that the rods, C, are in compression, and take up their own wear. This engine is well adapted for transmitting pressure to appliances which are worked intermittently, as, owing to the great speed at which it can be run, it will not only save the loss from friction (where gearing is employed), but will also reduce the friction in the machine itself by enabling the gearing Fig. 133 represents a small hydraulic engine—The Compton Hydraulic Motor—attached to and operating a gas-compressor. It shows a style of water motor in large use in connection with city water-mains. A pressure of 15 to 20 lbs. per square inch is sufficient to operate it; the motor here illustrated occupies a floor space of 9 x 23 inches; it will supply gas burners to the extent of 6,000 candle-power. Fig. 133. The valve motion on the motor is unique in this, the outlets and inlets have a positive motion by which they are simultaneously opened and closed by the motion of the piston; this valve motion is designed to overcome the back pressure; it has a governor, incorporated in the valve-motion for the purpose of maintaining uniform pressure on the main pipes. HYDRAULIC PACKINGS.Generally speaking a packing is a contrivance or a material to close a joint. Various greasy materials with gaskets, flax, hemp, etc., are used in joints which are screwed down, also collars of rubber, red lead, luting, graphite, etc. “U” Packing—Fig. 134. A most important part in the practical working of nearly all water-pressure machines is the leather collar, the invention It consists of a circular piece of stout leather (see cut page 20), in the center of which a circular hole is cut. This piece of leather is thoroughly soaked in water and is pressed into a metallic mould and so that a section of it represents a reversed U, and is fitted into a groove made in the neck of the cylinder. This collar being concave downwards, then in proportion as the pressure increases, the edge nearest the ram being trimmed down, it fits the more tightly against the ram plunger on one side and the neck of the cylinder on the other. It should be saturated with Neatsfoot or Castor oil so as to be impervious to water. Cup Packing—Fig. 135. When the least amount of friction possible is desired in the operating of a hydraulic plunger, there is no form of packing which can surpass a properly prepared and applied Leather “U” Packing (Fig. 134), and in practice its position is according to conditions, either in a groove near the upper end of the cylinder, or at the lower end of the ram. When for any reason it is not desired to use the outer lip of the packing, the resulting form is known as a Cup Packing, (Fig. 135), and when the inner lip is used then we have the Hat or Flange Packing. Fig. 136. Flange Packing. Fig. 136. When the water pressure is not over 2,000 lbs. to the square inch, and a greater allowance for friction is not important, a fibrous packing can be used, which is easier of application than these for large sized cylinders. The loss of power by the best of leather packings is 1 per cent. on 4 in. ram, 1/2 per cent. with 8 in. ram and 1/4 per cent. with 16 in. ram. HYDRAULIC |
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