TURBINE WATER WHEELS.

The word turbine is derived from the Latin, “turbo”—that which spins or whirls around—a whirlwind.

Fig. 117.

Theturbineis a horizontal water wheel, and is similar to thehydraulic tourniquetor 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 crudereaction wheelinvented by Barker about 1740; again a turbine is simply a centrifugal pump reversed, but the turbine is usually furnished with curvedguide vanesto guide the water as it enters the wheel.

Note.—Thesteam turbinehas 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 inFig. 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 eitheroutwardfrom a 1 central chamber, 2inwardfrom an external casing, 3from above downward, and, 4 frombelow; these constructions are either divided intooutward, vertical or central discharge wheels.

Turbines may also be divided intoreaction turbines, or those actuated substantially by the water passing through them (their buckets moving in a direction opposite to that of the flow);impulse turbinesor those principally driven by impact against their blades or buckets (the buckets moving with the flow); andcombined reaction and impulse wheelswhich include the best modern types of turbines. In reaction turbines thewheel passages are designed to be always full and therefore the water under pressure; in the impulse turbine the passages are not usually full.

Fig. 119.

Turbines in which the water flows in a direction parallel to the axis are calledparallel flow turbines—orjournal turbines.

Theturbine-dynamometeris 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 inFig. 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 interestespecially 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.”

Note.—The early history of the turbine is one of considerable interestespecially 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 turbinewheel is shown in the engraving,Fig. 120, page 129, whereN.N.represents the bottom casting of the case flanged to support the wheel by resting upon the bottom of the penstock.

The draft tubeIis of conical shape as represented atJ. 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 gatesH.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 rodsL. L., connecting with a rack and pinion which are manipulated by the operator as occasion requires, by an extension shaft from the couplingK, having a hand-wheel on top.

Fig. 121.

Power is transmitted from the wheel shaftFto 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 wheelGreceives the water as shown by the arrows atA, and hasa central and downward discharge, while the lower wheelCreceives the water as shown by the arrows atBand has aninward, downward and outwarddischarge as shown by the arrows atD.

These two sets of buckets need to be exceedingly strong. The lower setBare 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 ringC, surrounding the outer and lower edges. This ring is a part of the diaphragm which separates the two wheels. The upper edge of the ringCis 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 shaftF. 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 atE, 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 ithas passed through the wheel, as it flows away into the tail race. Any slight variation in the form of buckets or admission apertures will make an appreciable variation in the quantity of water discharged by a turbine wheel.

These wheels are made either for vertical or horizontal shafts and are also made single or double. The engraving, Fig. 122, shows aHercules 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 curbor 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 ofthe 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 21⁄2inches 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 showThe 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 wheelin 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 thehole in the floor, as it will be much easier to dress off with a plane than the plank floor. The floor should be supported by posts under the timbers around the hole, so that there will be no settling of the floor after being once made level. As the flange on which the wheel rests is turned true, the wheel will, when placed on this level floor, stand in the exact position required,i.e., the shaft will be exactly vertical.

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. 124shows 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 ironcases and penstocks are much better than could be possible with wood, on account of their durability and freedom from leakage.

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 aniron 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 whomay consider the use of water power, if a few general remarks on this subject are added.

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 ofthree feet per secondis good practice in short tubes of uniform section of not more than fifty feet in length; butthe 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 Turbineis 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 pitand a side viewof 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 71⁄2feet in diameter. The shaft of the turbine is a steel tube 38 inches in diameter, built in three sections, and connected by shortsolid steel shafts 11 inches in diameter, which revolve in bearings. On the top of each shaft is a dynamo for generating the electric power.

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. 128gives 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 311⁄2inches and the outer radius is 371⁄2inches, 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.

InFig. 127is shown a half-plan of one of the wheels, in a part of which are seen theguides 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 turbinesfor the three positions of the gates correspond to the three horizontal stages or openings through the guides as shown inFig. 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 821⁄2per cent.

Fig. 127.

The average discharge through one of these twin turbines is about 430 cubic feet per second, andthe theoretic powerdue to this discharge is 6,645 horse-power. Hence if 5,000 horse-power be utilizedthe efficiencyis 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 1411⁄2feet 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.

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