Opinions differ as to whether the water-wheel almost universally known as the Pelton type belongs to the impulse, the tangential, the reactive, the jet or the percussion class, or to a cross between two or more of these classes. The fact is, that for an almost infinitesimal part of a second the axis of the jet of water strikes the bucket of this wheel at a true tangent to its base-line. The percussion of the water, striking the bucket, imparts an impulse to the wheel, causing rotation; and generally the bucket is so shaped that the direction of the jet is reversed almost back upon itself. This reversed flow, as it emerges from the bucket, is reactive, and tends to further increase of the speed and power of the rotation. There is hardly a law in all the vast category of the application of forces which is not applicable to the resolution of the problems embodied in the design and operation of these water-wheels. To avoid objection, we may term the general type “ tangential,” as distinctive from water-wheels of the turbine class.
The true principle of the tangential wheel was illustrated and described by Branca in 1629. This device was used in Loretto, Italy, and is pictured as a horizontal wheel with vanes or buckets, upon which a jet of steam impinged, causing rotation. This was imparted through a bevel-gear to a shaft that dropped pestles into respective mortars for grinding, as in a stamp-mill. In later times Poncelet (1827) demonstrated the inefficiency of flat vanes, and substituted therefor forms which were concave and tangent to the jet, so that the water, on entering, would run up inclines and back again, thus imparting energy to the water-wheel during its entire course. This was the first form of tangential wheel to “ provide graduated entrances and avoid shocks, concussions or eddies in the water.” Prior to 1822, however, James White had used semi-circular buckets; and in 1843 Madame de Girard of Paris brought out the semi-circular buckets which have since become widely known as the distinctive feature of the Girard water-wheel. De Canson (1847) used quarter-circle buckets to which the jet was applied normally, the water escaping tangentially. Borda, in his memoirs (1767), gave the sum and substance of tangential water-wheel principles when he wrote : “ To produce its total mechanical effects, the water serving as a motive power must be brought on to the wheel with impulse, and quit it without velocity.” Euler’s description of the first-constructed turbine (1754) considered the motion of water in a semi-circle, while imparting power to a wheel. Dingler (1858) gave forms of water-ways which conform well with the half-circle motion of water in driving a tangential wheel. Navier (1819) refers to the mills of Provence and portions of Dauphiny, which had spoon-shaped buckets, receiving the stroke of water, delivered generally through inclined troughs. Again, in 1819, Navier wrote : “ The necessity of disposing machines in such wise that there should be no shock, although established long ago, both by theory and practice, is not so generally recognized as could be desired.
Mr. Brewster also announces that he has frequently had the idea that a hydraulic machine of great efficiency could be constructed by combining the impulsion with the reaction of water.” Ferguson (1826) described an undershot wheel, having buckets inclined to the radius and “ driven partly by impulse.” Schwamkrug, prior to 1850, constructed vertical tangential wheels with outward flow. In short, numerous other instances might be cited to prove that the modern tangential water-wheel has been brought to its present state of high efficiency through gradual evolution from times of antiquity.
In bold relief, however, stand the names of a few men who, in recent years, have developed these wheels from the crude devices of the first part of the century to the high plane which they now occupy as prime movers in the industry of the world. To make reference to the work of these inventors, and then to discuss the engineering features involved in the design and construction of highly efficient tangential -water-wheels, and to consider the tendency of modern practice in this respect, is the purpose of this paper.
Tangential water-wheels are essentially a Californian development, in that their perfection was brought about through the natural conditions imposed in the mining regions of the Golden State, where limited quantities of water at high heads constituted practically the only form of water-power available for the working of mines and mills. But the use of water in limited quantities at high heads necessitated the use of a form of water-wheel entirely distinct from the familiar undershot and overshot types. Others, however, had been working on the same problem as that which confronted the California pioneers, and among these was notably Jearum Atkins, to whom must undoubtedly be given the credit for having been the first to grasp the true principles underlying the operation of the tangential water-wheel by impulse and reaction, and to design a wheel of this type which soundly embodied modern ideas in that direction. The remarkably advanced mechanical ideas of Atkins were first brought before the engineering world by Mr. R. D. O. Smith and simultaneously by Mr. John Richards in articles published in December, 1893. Among his other inventions, Atkins applied in 1853 for a United States patent on a new form of water-wheel. The patent was not issued until August 10, 1875; and its drawings and specifications show that the inventor had two prime ideas in mind, the minor of which was the building of a wheel containing semi-circular water-ways, of even width and area throughout, and parallel with the axis of the wheel; the water being applied to these buckets simultaneously from a trunk surrounding the wheel. One of the drawings in the Atkins patent is shown in Fig. 1. The major idea of the Atkins patent is that the water in the wheel, as well as the wheel itself, should move at half the speed of the entering water, to facilitate which result, Atkins proposed that the area of the water-way through the wheel should be double the area of the water-way to the wheel. Moreover, his specification declared that, since the peripheral speed of the wheel would be half the velocity of the jet, and since the direction of the jet would be reversed by the shape of the bucket, the water must leave the wheel without velocity, or, in other words, the water should give up all its energy to the wheel.
So far as is known, Atkins never built a wheel upon these principles; but those who know of the serious misfortunes which always pursued him can easily understand why this was never done. The commercial value of the Atkins wheel has, therefore, never been determined. But, while it differed in shape from the present forms of tangential wheels, and had no dividing-wedge in its buckets, it clearly embodied the fundamental principles of the modern tangential wheel, namely, that the water be applied to the periphery of the wheel; that the peripheral velocity of the wheel be approximately one-half of the velocity of the jet; that the direction of flow of the stream be reversed, so that the wheel may absorb the reactive energy of the jet; and that the water leave the wheel without velocity. A significant evidence of the lack of appreciation which American engineers have shown for the value of the Atkins patent is found in the fact that, seven years after it was granted, Messrs. Escher, Wyss & Co., of Zurich, Switzerland, began making water-wheels of the Atkins type, and the practice soon extended all over Europe, especially France. The Atkins type of wheel came back to this country in 1890, however, through the plans for the water-wheels at Niagara, which were made from drawings furnished by Messrs. Faesch & Picard of Geneva, Switzerland, who, with four other European firms, tendered full plans for the construction of these wheels.
Opinions differ as to the relevancy of the Atkins wheel to a discussion of the priority of invention of the tangential wheel; but in view of the plain facts, I must confess my inability to understand any contention that Atkins’ invention has no bearing on that subject. It is true that he neither proposed the use of a split bucket nor suggested that the buckets should enter and leave the stream without shock; nor, indeed, did his wheel have the form or many other features possessed by the tangential wheels of to-day; nevertheless it embodied their basic principles with thoroughness and clearness. The truth of this was recognized in the two articles already referred to. Mr. Smith says:
“ The writer does not propose to discuss the mechanical or theoretical value of this invention further than to suggest that, while, for the enormous pressures under which the Pelton wheel acts, the round nozzle and free jet may be a preferable form, it does not appear to follow that the Pelton wheel is necessarily a more perfect form than the Atkins wheel with its semi-circular buckets, its confined water, and rectangular jets under low pressure. The advantages of the Pelton wheel may be quite dependent upon other considerations, viz., the absence of inclosures and joints capable of withstanding enormous hydraulic pressures, and the absence of friction incident to close fittings capable of withstanding such pressures. It would seem to the writer that the Atkins wheel approaches theoretical perfection as closely as human mechanisms ever approach it, and that the Pelton wheel is a wonderfully successful adaptation of Atkins’ discovery to special circumstances.”
Mr. Richards says :
“ In this country the earliest understanding of impulsive action, as distinguished from pressure in turbine water-wheels, seems to have been arrived at by Mr. Jearum Atkins.”
And after describing the Atkins wheel and the principles involved therein, Mr. Richards concludes:
“Mr. Atkins, more than forty years ago, had thus arrived at a point in this branch of engineering investigation that not very many of the present day have reached ; and much honor is due him for his researches, which, if followed out at the time, might have added millions of wealth to this country.”
But the Atkins wheel was unknown until the patent was issued in 1875; and in the interim between his application for a patent and its issue, the miners of California had independently developed the “ hurdy-gurdy ” wheel, which, though crude, was the immediate forerunner of the modern type of tangential wheel. The original hurdy-gurdy wheel (named after the musical instrument in which a revolving cylinder takes the place of a fiddle-bow, operating upon strings) resembled a circular-saw with straight-cut teeth more than anything else; the chief difference being that the hurdy-gurdy was made of wood, varying in thickness up to 2 or 3 inches or more. The jet was applied exactly as in present forms of tangential wheels; and the power derived therefrom showed an efficiency of 40 per cent, or thereabouts.
The hurdy-gurdy wheel was made of blocks of wood about 4 inches thick, cut out, as stated, like the teeth of a circular-saw, about 8 inches apart. These teeth or buckets were then closed in by casings of wood which formed the sides of the wheel; and from these sides four arms or spokes were morticed into a log, the end of which was fitted with a round gudgeon for a bearing. The gudgeon was then placed in a live oak block, which had previously been gouged out for the bearing, very roughly, by the way, because of the poor quality of the tools available to the miner of those days. The water was applied at first in the form of a jet, emanating from a hole bored into the end of a wooden block with which the pipe had been plugged. The pipe-line was sometimes of sheet-iron and sometimes of wood. With heads varying from 40 to 50 feet, square wooden pipes were frequently used. These were merely square wooden boxes, bolted together with iron rods, if such could be secured; otherwise the box would be clamped together by means of wooden frames, cleats and wedges.
Such hurdy-gurdy wheels and wooden pipe-lines were considered good practice in 1854; but, as time passed and small quartz-mills were erected, it was found that the sphere of usefulness of the hurdy-gurdy could be enlarged to include the driving of stamp-mills, which it did fairly well, when brass nozzles and moderately high heads were used, as became the common practice. The question of efficiency was not taken into consideration until hurdy-gurdy wheels were applied to the operation of large stamp-mills, when it was found that the hurdy-gurdy would not develop the power required to give the mill the proper speed. This was attributed to the fact that, as the buckets were closed in at each side and on the bottom, the waste-water could not discharge itself freely, and, in consequence, the buckets would remain full during the greater portion of the time they remained in the jet, while all additional water directed against the bucket after it was filled merely slipped over the face of the water already in the bucket. The hurdy-gurdy was a pure impact wheel; and, at that time, little if any thought had been given to the reaction of water as applied to the present forms of tangential wheels.
The gradual evolution of the hurdy-gurdy wheel into the modern tangential wheel was centered in operations mainly confined to Amador and Calaveras counties in California. About 1866 the Pacific Iron-works of San Francisco made a cast-iron wheel to drive a 16-stamp mill at the Gwin mine in Calaveras county, which was the first wheel to embody a material change in the action of the water from that which occurred in the hurdy-gurdy. It had a center-discharge, for the purpose of diverting the direction of the stream, so that the energy which the stream still possessed, after it had lost the portion due to the initial impact could be rendered useful by being guided in a reactive course. The great success of this wheel, as compared with the hurdy-gurdy, proved to be the turning-point in the building of this class of wheels; and it was realized at once that the old hurdy-gurdy had seen its best days.
The next marked improvement was undoubtedly due to Mr. S. N. Knight of Sutter Creek, Cal., who brought out the cup-shaped bucket since universally known as characterizing the Knight wheel. This wheel is of the true tangential type, and its buckets are so shaped that they have both side- and inward discharges, while most of the later types of bucket have mainly side-discharges. The stream of water applied to the Knight bucket is of rectilinear cross-section. The first Knight wheel, made in 1870, presented no radical departure from the present form of the Knight wheel. In 1872 a Knight wheel, placed in the Gwin mine to operate a 20-stamp mill, was first equipped with buckets having an inward discharge; these were then changed so as to have side-discharges; and finally the present form was adopted, which has both inward and side-discharges. This being an important stage in the development of the tangential wheel, it is pertinent to quote the following statement by Mr. Knight concerning the early history of the invention :
“About 1870 I, in common with others, made water-wheels entirely out of wood. The buckets were shaped like saw-teeth, and wooden flanges covered the sides of the buckets, to confine the water; a round nozzle was used; and the general results were considered at that time highly satisfactory. The next step, about two years later, was to make a wooden wheel with iron buckets, giving them a curve and discharging the water toward the center of the wheel—still using, however, the round nozzle.
“Two years later than this, Nicholas J. Colman patented a wheel which had a bucket shaped very much like the present Pelton bucket; the stream splitting and curving off to each side. He, for lack of means, I understand, did nothing with it.
“After two or three years more had passed, I made an improvement by using a curved iron bucket and having the discharge towards the center and to one side, much the same as the Collins (Pacific Iron-works) wheel, still using the round nozzle.
“After continued experiments with the nozzle, Collins found it did not fill the general requirements ; he could not cover enough bucket-space along the periphery of the wheel, without covering an equal space in the width of the bucket, by increasing the diameter of the round nozzle.
“ This induced him to try an elliptical or oblong nozzle ; and the first wheel of this character was placed in the Lamphear mine, at Mokelumne Hill, and it was quickly followed by two others, so satisfactorily did they work.
“From these wheels sprang the present Knight water-wheel; for here it was that I conceived the idea of abandoning entirely any direct modification of the round nozzle, and made the opening a narrow rectangular slit.
“ The round nozzle did well enough where small quantities of water were used ; but upon using considerable water, the nozzle became so large that, while the upper edge could be brought near the wheel the lower edge was far away, and it reduced the power materially ; so the slit was determined upon. More than one nozzle was also tried, but it did not prove satisfactory.
“ In 1875 the first wheel of the present style was placed in the Lincoln mine, at Sutter Creek, and from that time various improvements have been made in the size and arrangement of the slits in the nozzle and shape of the buckets. ’’
We now come to a vexed question, namely, the origin of the jet-splitting wedge. If the records of the United States Patent Office form any criterion, or if after-events of commercial import have any significance, the credit for the wedge-shaped bucket is due to Mr. Nicholas J. Colman of Railroad Flat, Cal. (1873). The specifications of the Colman patent describe a tangential wheel built somewhat after the hurdy-gurdy principle, but with sharply defined buckets containing wedges for dividing the stream. In substance, the specifications describe the action of the water to be as follows: Leaving the penstock, the water strikes the wedge and back of the bucket, exerting its first force upon this back. The wedge divides the water, which then follows the upwardly and outwardly sweeping curve of the discharge-passage, still exerting its force upon the full length of the buckets, while combining its momentum with the centrifugal force acquired by the wheel, and finally discharging at the periphery, through openings which are provided therefor. The two claims of the Colman patent read as follows:
- The wedge- or plow-shaped buckets, dividing the water at e, and curving toward the sides at f, substantially as and for the purpose described.
- In combination with the wedge-shaped buckets, as shown, the upwardly curving buckets g, discharging at the periphery, substantially as and for the purpose herein described.
Mr. Knight is my authority for the statement that, to the best of his knowledge, Mr. Colman made a bucket for splitting the stream as early as 1870 ; but so far as Mr. Knight knows, none of the Colman wheels were ever put into use. In any event, it is certain that tangential wheels made under the Colman patent were never brought before the public as a regular manufacture, nor did that patent exert any influence in molding the form of the bucket of the tangential wheel of the present time. It is interesting to note, however, that a few years before the expiration of the Colman patent it was bought from the inventor for $500—which proved to be a very good investment, as the purchaser secured thereby a royalty of $1 for each foot of the diameter of every Pelton water-wheel sold during the life of the Colman patent, upon which basis of settlement he netted about $15,000.
There are several others who claim the invention of the Pelton form of bucket—that is, the bucket containing a dividing-wedge. Among these claimants may be named as prominent Mr. Joseph Moore of the Risdon Iron and Locomotive-works, San Francisco; Prof. F. G. Hesse, Professor of Mechanical Engineering of the University of California; and Mr. L. A. Pelton, inventor of the Pelton water-wheel. According to the statements of these three parties, given below, the divided-wedge form of bucket was invented between 1865 and, say, 1878.
In February, 1897, Mr. Moore issued a monograph in which he claims to be the inventor of the then so-called “ California tangential water-wheel with reaction-buckets.” From 1860 to 1880 Mr. Moore was manager, constructing engineer, director and part owner of the Risdon Iron-works, the records of which institution bear irrefutable support to the statements of his monograph. The substance of this pamphlet, which is quite long, is that in March, 1874, Mr. G. Tiscornia of San Andreas, Calaveras county, Cal., applied to the Risdon Iron-works for information respecting a water-wheel to drive a quartz-mill. After computing the amount of water and head available, Mr. Moore found that it was impracticable to perform the specified work with the hurdy-gurdy wheels then used, in view of which he “ suggested to Mr. Tiscornia a change of buckets, so as to gain reactive effects, also avoid oblique impingements,” further stating that he (Moore) would send Tiscornia a sketch of buckets accordingly. “After some correspondence on the subject,” continues Mr. Moore, “I made, on March 29, 1874, on an order-blank of the Risdon Iron-works, the sketch ” which is reproduced herewith as Fig. 2. On the opposite side of the sheet containing the sketch Mr. Moore wrote a letter to Mr. Tiscornia, dated March 29, 1874, which stated:
“You can see the principle (of the wheel), viz.: to receive the water without shock, at an angle of about 10 degrees, and deliver it at the same, or say 15 degrees. This reaction-water will have no velocity when at proper speed, but will probably react or spout in the opposite direction ; really, its best speed is when it drops straight down, but practically it is best to leave enough velocity in it to clear the wheel.”
On the next day (March 30, 1874) Mr. Moore again wrote to Mr. Tiscornia, the letter being as follows :
“Yours of the 26th just came to hand. Last night I mailed you a sketch of a bucket which I think is quite superior to the one you sketched. It has the same advantages that you expect with yours ; that is, reverses the direction of the water without shock, which is all that can be accomplished by any bucket; but mine has the further advantage of getting rid of the water without its coming in contact with the next bucket, which is a decided advantage, as you see that the water has become stationary with respect to the wheel, or, what is more likely, has got a backward motion ; then the following bucket must impart the velocity of the wheel to the water again, which is just the same as an overshot wheel running in back-water. The proper way is to do the work and get rid of the water, and this, as you see, is accomplished by my bucket, upon which there is no patent.”
The monograph then expresses the opinion that “ not only was the theory (of the tangential wheel) thus laid down, but it was carried out in a manner not since improved upon.”
The order was duly entered in the Risdon order-book, April 7, 1874, for “ a set of hurdy-gurdy wheel buckets, as per pattern and sketch.” The buckets were finished and shipped by express to Mr. Tiscornia on April 13, 1874, and on the same date Mr. Moore wrote to Mr. Tiscornia, saying, among other things :
“You will find, if you let the water play upon the center, that it shoots back with sufficient clearance to free the following bucket. These buckets ought to be 7 to 9 inches apart and the water led on the wheel at an angle not more than 15 degrees, and from a good nozzle, as close up as possible to the buckets.”
None of the old castings for the Moore buckets can be found; but, fortunately, the pattern from which they were cast was found in the pattern-room of the Risdon Iron-works. The pamphlet contains front and rear views of this pattern (Fig. 3), together with a transverse section thereof (Fig. 4) made from templates fitted to it, the scale being reduced by photography to one-half of the original size. A diagram showing the method of mounting the buckets is also reproduced (Fig. 5). At the Risdon Iron-works may be seen the originals of these patterns, drawings and documents, together with the affidavit of George Cummin, general foreman of the works, as to when the buckets were made, and the affidavit of John F. Skivington, who made the pattern for the bucket, and who is still foreman of the Risdon pattern-shop.
Mr. Moore’s pamphlet (p. 7) states that, “ after some correspondence on the subject,” he made the sketch referred to. The probability is that this correspondence followed an interview with Professor Hesse, which was had presumably with the idea of confirming, as far as possible, Mr. Moore’s theories.
In May, 1897, Mr. Pelton published a pamphlet on the “Origin of the Pelton Water-wheel,” containing the following statement, which may therefore be accepted as an authentic presentation of Mr. Pelton’s claims to the priority of invention:
“I crossed the plains from Ohio in 1850, and engaged in mining almost continuously until 1864, when I took up mill-wrighting, in connection with mining, at Camptonville, Yuba county, and other places north of that town, in which business I was employed until 1878; and during this period I constructed a number of water-wheels, of the type commonly known as hurdy-gurdy wheels, having an efficiency of 40 per cent, and upwards, according to the style of buckets used. Here, I conceived, was a chance for improvement ; and early in 1878 I procured the necessary appliances for testing the efficiency of buckets for pressure- or jet-wheels, and devoted most of the time for two years following to designing a bucket which would give a higher efficiency. I tested between thirty and forty different shapes of buckets, and finally noticed that a curved bucket having a jet-strike on the side, as in Fig. 7, instead of in its center (Fig. 6), gave a marked increase in the efficiency of the wheel, but caused an end-thrust against one bearing. To avoid this, I experimented with placing the buckets alternately, as in Fig. 8, when it was but a step to combining the two curved buckets and splitting the stream, as in Fig. 9. This bucket, when tested, gave such astonishing results that I immediately took steps to secure my invention.
“ I introduced my wheel to the public, after obtaining a patent, in October, 1880, and claim to have invented what is known as the ‘ Pelton water-wheel ’ independently, and without any knowledge whatever or aid from the efforts of others in that line.”
This statement is plain, straightforward and convincing; and the writer is but one of many who believe that Mr. Pelton is entitled to the credit he has claimed. Moreover, an analysis of Mr. Pelton’s statement is interesting. In discussing the matter, Mr. Pelton stated to two hydraulic engineers well known to the writer, that at one time, during experiments with a Knight wheel, the key securing the wheel to the shaft loosened, allowing the wheel to become laterally displaced on the shaft, so that the stream of water struck the buckets on their inner side; and that, as a result of this displacement, it was observed that the stamp-mill which the wheel was driving ran faster. This corroborates the statements of Mr. Pelton relative to Figs. 6 and 7, the first of which represents the Knight wheel at that time, while Fig. 7 shows the same bucket as it appeared after the Knight wheel had been displaced, as described. Of course the application of the jet in the manner shown in Fig. 7 would cause an end-thrust against the bearing on the jet-side of the bucket, to obviate which, the alternation of buckets shown in Fig. 8 would naturally suggest itself. As Mr. Pelton says, it would then be but a step in the evolution of the bucket to combine the right and left buckets of Fig. 8 to the simple stream-splitting bucket shown in Fig. 9. It is of further interest to note that the arrangement of the buckets in rights and lefts, as Mr. Pelton states, antedates the distinguishing feature of the Tutthill water-wheel. Moreover, Mr. Knight says that he also experimented on buckets in rights and lefts early in the ’70s, but abandoned the arrangement as being of no advantage to his form of water-wheel.
It seems that Professor Hesse has never made, of his own volition, serious claim to the invention of the divided bucket, but was drawn into the controversy by Mr. Pelton in the hope of disproving Mr. Moore’s contention. The part that Professor Hesse took in the development of the divided bucket appears in a communication to Mr. Pelton dated May 19, 1897, in which Professor Hesse states that some time between 1865 and 1868 Mr. Moore called upon him (Hesse) and asked his advice as to the best water-motor answering the following conditions: high head, good efficiency, and such construction as to admit of its being built of wood at the mill, except flanges, shaft, and such light castings as could be readily transported on pack-animals, Professor Hesse’s reply is best given in his own words :
“ It is clear that, under the above conditions, only those water-motors deserve attention in which the energy of the water to be converted into work is received by the wheel in the form of kinetic energy. The tangential wheel with horizontal axis, a desirable condition, requires to be charged on its inner periphery, necessitating a large angle of entrance (the angle formed by the jet and the tangent to the wheel), causing a diminished efficiency and entailing, on account of limited space, a more costly construction. A wheel of the Jonval type with horizontal axis, the water flowing in planes parallel to the axis, seemed to answer best. It has, however, the disadvantages of being unbalanced: a serious point, considering the ever-shifting movement about the center, great number of revolutions, and large radius. Adding to this the necessity for a great number of buckets, with great length of water-way, to cause a proper discharge between the limited angles of entrance and discharge, it is clear that such a wheel would be heavy and of costly construction. I was aware of the fact that two such wheels, mounted on the same shaft, had been used heretofore to balance (see Fig. 10). Then it occurred to me that two such wheels might be placed together, so as to form one wheel, and one bucket out of every pair of buckets, reducing thus the entrance angle to 0, causing an increase of efficiency (Fig. 11). The jet entering in a direction tangential to the wheel is divided and discharges in two streams at the opposite sides of the wheel. Another advantage is to be found in the increased passage-way of the discharge-water, one on each side of the bucket, a fact which greatly lessens its weight and facilitates its free discharge. The best form of bucket could only be determined by actual tests and experiments, which were not made for lack of time. I furnished drawings for such a bucket to Mr. Moore, and was afterwards informed by him that castings were made from this design, and were sent to a mine to be bolted to the rim of a wooden wheel. The result of the performance of the wheel, provided it was built, never reached me. Having never contemplated taking out a patent for what I considered so obvious an improvement, I lost sight of the matter from that time.”
While it is cheerfully conceded that Mr. Pelton may have made his invention without cognizance of the work previously done by either Mr. Moore or Professor Hesse, the fact remains that his work was several years later than theirs. To a considerable extent, both Professor Hesse and Mr. Pelton rely on memory alone for dates; and in view of the documentary evidence produced by Mr. Moore, it is clear that Professor Hesse is in error in stating that Mr. Moore asked his advice on the subject “ at some time between 1865 and 1868.”
The writer is therefore convinced that Mr. Moore and Professor Hesse were the first to suggest the generally adopted form of the tangential-wheel bucket, containing the dividing- wredge to direct the flow of the water in reversing its direction.
But the statements of these three highly respectable men are given especially to show that different minds were working simultaneously upon the same problem. Did time and space permit, the efforts of many others in the same direction could be similarly detailed, conclusively demonstrating that the evolution of the tangential water-wheel bucket has had a history in which have figured not only the names of Atkins, Knight, Colman, Moore, Hesse, Tiscornia and Pelton, but also, and largely coincident with them, those of James Patterson, Louis Biggio, John B. Pitchford, S. L. Berry, Francis M. F. Cazin, Daniel Hug, W. G. Dodd, the Risdon Iron-works (San Francisco), and the early wheels of D. Donnelly of Sutter Creek, and Watson of Nevada City, Cal., as well as James Leffell & Co., the Risdon Iron-works, and the Abner Doble Co., with their respective Cascade, Risdon and Ellipsoidal wheels respectively. Still other wheels might be mentioned, such as the Kale, Ridgway, Bookwalter and Tutthill. The forms of the Pelton and Dodd buckets are shown in Figs. 12 and 13 respectively.
Of these buckets, the Biggio is the only one that does not claim distinct advantages from the use of a sharp central and radial division which splits the stream. In the Biggio bucket, which is shaped something like the letter “ W,” made with low rounded turns instead of angles, the central ridge is but a partial division. The Pitchford bucket contains a sharp, radial dividing-wedge, and the front or outer lip of the bucket slopes towards the direction of rotation, so as to prevent this outer lip from striking the jet when the bucket enters the stream. This patent also provides a means whereby “the true apex of the bucket” may be centered in the stream. The Berry patent (Fig. 15) contemplates a divided bucket of such shape as to present, in the plane of rotation, surfaces at right-angles with the stream, permitting a free discharge tangential to the wheel, and avoiding disturbance of the stream on entrance. This the patentee endeavors to obtain through the use of convex instead of concave surfaces for the faces of the buckets which are presented to the jet. The Cazin patent partakes of Pitchford’s idea, in that its bucket is intended so to enter the jet as to prevent the slapping of the stream by the lip of the bucket. Cazin professes to accomplish this by projecting the peripheral lip or edge, still using radial wedges (as do all buckets other than the ellipsoidal, which will be described later). The Cazin bucket divides the stream in two entirely distinct planes, viz.: first in a plane parallel to the axis of the wheel’s rotation, and, second, in a plane at right-angles thereto, or in the plane of the wheel’s rotation. The Cazin wheel, moreover, is so designed that the entering lip, which is transverse to the plane of rotation, first enters the stream, but the end of this entering lip travels a path of greater radius than that which is covered by the bucket proper; therefore as soon as it enters the stream the jet is deflected, so that it misses the bucket next in advance of the entering one. Cazin thus not only loses the direct effort of the stream, but, by missing that bucket entirely, the possible reactive effect of the water thus deflected is lost. The same is true, however, in smaller degree, of practically all the other types of buckets having straight entering lips, as will be more fully shown further on. The Pelton, Risdon, Hug, Cazin and Dodd buckets are characterized by the broad edge which forms the entering lip of the bucket. This lip, in conjunction with the splitting-wedge, exerts a twofold influence upon the stream; first, the entrance of the bucket into the jet causes the stream to be split by the entering lip in a plane that is axial to the wheel; secondly, as the portion of the jet which is diverted into the bucket encounters the splitting-wedge therein, the water is again divided, and, instead of pursuing its natural flow, is ordinarily forced to follow a path provided for it. These lipped buckets are, therefore, objectionable in several respects. They not only divert the stream from its natural course while the lip is passing through the stream, but they also break up that part of the stream which is entering the buckets, setting up in the water a violent swirling action, which prevents its smooth flow through the buckets. This not only cuts the buckets, but also destroys the best results of reaction of the water, and causes an additional loss of efficiency through the reaction of part of the discharged water against the back of the next following bucket (see Fig. 14). The Dodd bucket, which has been acquired by the Pelton Water-wheel Co. and, in a slightly modified form, is gradually displacing the original form of Pelton bucket for high heads (the form always meant in this paper when the “ Pelton ” bucket is named) partly obviates the inherent disadvantages of the straight-lipped bucket by giving the entering lip a curved-in form, which more quickly envelopes the stream than it is possible to do with a straight edge. The Ridgway, Bookwalter, Kale, Watson, Tutthill and Cascade wheels form a class by themselves, in that the buckets are placed alternately on the sides of the wheel rim, that is in rights and lefts. Ridgway placed two directing ribs equi-distant through the radial line of the bucket, the shape of which bears a strong resemblance to the cups used on belt elevators for hoisting grain. The Bookwalter bucket had a simple cup-shape, and was so arranged on the periphery of the wheel that but half of the jet
entered each bucket; that is, the inner edges of the alternate buckets did not overlap. The difference between the Book- walter and the Tutthill wheel, therefore, rests mainly in the fact that in the Tutthill wheel the entire jet as a unit goes into the buckets. In the Watson, Kale and Cascade wheels, the central dividing edge is placed around the periphery of the wheel, in the plane of its rotation, and central to the jet; and on the opposite sides of this dividing edge the buckets are placed in rights and lefts. In the Kale wheel the buckets are but straight paddles as in the familiar flutter-wheel, while the other wheels use cup-shaped buckets.
An ideal bucket for a tangential water-wheel, that is, a bucket from which would be secured the greatest effective power for the energy applied, would receive the stream of water in a solid condition, reverse its direction without breaking it up into spray, and discharge it along natural lines in an even flow over the whole bucket-surface. Its form would be such that the plane of the bucket, say, at the edge of the dividing-wedge, would always be perpendicular to the direction of the stream. Finally, the force exerted by impact and reaction from the stream would be equal, whatever angle the plane of the bucket might bear to the axis of the jet. Of course every effort should be made to minimize the friction between the stream and the surface of the bucket (a principle opposed to the idea which prevailed in the design of the Biggio bucket); to give ample clearance between the buckets, that they may discharge freely; to give each bucket the longest possible arc of contact with the stream; to avoid beating or slapping the stream with the lips of the buckets ; and so to dispose the buckets that each, as a whole, will enter and leave the stream with the utmost quickness.
The buckets of the most familiar forms split the stream on entering it, in two planes, viz.: the entering lip splits in the plane transverse to the wheel’s rotation, while the dividing-wedge in the center of the bucket splits the stream in the direction of the wheel’s rotation. The transverse splitting is both unnecessary and undesirable. A bucket which will not split the stream transversely, and which is of such a shape as to preserve the perpendicular position relative to the stream above specified, is found in the ellipsoidal type, which has no entering lip, and the shape of which is described from true hydraulic curves. Interesting illustrations of the above propositions are furnished by buckets taken from wheels which have been run with water containing sand, grit or “ slickens.” One of them, of the Pelton type, is shown in front and back views, respectively, in Figs. 22 and 23. Under these conditions, the faces of the buckets are badly worn from striking against the jet; the corners within the buckets are deeply cut or perforated, according to the time of service (in this case, 8 weeks); and the inner corner of the back of each bucket, is similarly worn and perforated from the backward discharge of the immediately preceding bucket. These erosions are all due to the swirling of the water because the bucket is so formed as to prevent proper discharge. The reason will be clear from an examination of Fig. 14. The jet, striking on the inner side of the face of the bucket, glances off the surface at an angle equal to that of incidence; and this action occurs at three points within the bucket, namely, on its front, bottom and rear faces, as is clearly shown by lines of erosion cut by the sediment carried in the water. As an inevitable consequence, a swirling action will take place at the corners f, g and h,Fig. 14, resulting in great loss of energy and the eventual perforating of the bucket at these points.
Buckets made on true hydraulic lines show no pitted erosion; such wear as occurs in them is uniform and even throughout. Figs. 30, 31 and 32 represent an ellipsoidal bucket which has been in continuous service for twelve months under a head of 400 feet at the Dreisam mine, W. Moorehead, Superintendent, Soulsbyville, Tuolumne county, Cal. Here the water contains much grit; from 2 to 3 tons of sand per day passing through the pipe-line and being shoveled out from the tail-race daily. Fig. 30, a face-view, shows the smooth uniform wear on the active and reactive faces of the bucket, which are entirely free from erosions such as would occur from swirling water. This also indicates a uniform discharge of the water around the entire discharge-edge of the bucket. Fig. 31, likewise a face-view, shows the wear on the dividing-wedge, which, being greatest at the middle of the bucket, demonstrates that the maximum effort of the water is at this point, where it would produce the best results. Fig. 32 is a back-view of the same bucket, showing absolute freedom from any impingement of the water on the back of the bucket, the skin of the casting remaining as it originally left the mould. The smooth wear of this bucket, with the total absence of any eddy-action, is believed to prove the correctness of the hydraulic curves, and likewise of the theories on which the design of the bucket is based. Note in Figs. 30 and 31 the slight depression in the center of each bowl of the bucket. This depression is directly opposite the reinforcing ribs on the back of the bucket (see Fig. 32); and the additional wear at this point was caused by the difference in the hardness of the casting. The metal where the reinforcing rib joined the bucket, having more body, cooled more slowly in the mould than the other and thinner parts of the bucket, causing the metal at this point to be slightly softer; whereas the iron in the thin section of the bucket showed a tendency to chill, and thus permit the greater erosion at this point. The shape and location of this depression clearly prove this.
To appreciate these points fully, it must be borne in mind that, unless the stream enters the buckets from their sides, simple cup-shaped buckets, without dividing-wedges, permit the accumulation of dead water at the base of the cup. The splitting-wedge was devised to do away with this dead-water, and to extend an invitation to the live water to turn its direction back upon itself, that it might, by reaction, impart further energy to the wheel. The invention of the dividing-wedge, therefore, constituted a long step in the right direction. Again, the maximum torque which a tangential wheel, held stationary, will exert, will be given when the direction of the jet is, as stated, perpendicular to the plane of the bucket; that is to say, the angle of the maximum effort which a jet can exert is tangential. There are two ways by which this condition may be satisfied, one of which is impracticable, while the second is simple and effective. The feathering paddle-wheel offers the key to the first solution, for, as it always enters the water at right-angles, it would keep the plane of a water-wheel bucket perpendicular to the axis of the stream during the arc of contact. But the application of this device to tangential wheels, with their high rotative speeds and centrifugal force, presents mechanical difficulties which preclude all hope of success. The second solution is found, deeply veiled, in the Berry bucket (Fig. 15), the reciprocal of which furnishes such hydraulic curves for the faces of buckets as will give a smooth and uniform distribution of forces over practically the entire surface of the bucket, regardless of its position in the arc of contact with the stream. This feature is more fully developed in the ellipsoidal type, to be further discussed below.
The ideal bucket should possess some other important features. The manner in which the jet is brought into contact with the bucket is of paramount importance. All will concede that the stream should enter the bucket in a solid condition; in other words, it should be disturbed in the least possible degree. The entrance lips in use are either straight or in-curved. The great majority of buckets have the straight lips as in the original Pelton, the Risdon, Hug, Cazin and other well-known forms. The main example of the curved entrance lip is found in the Dodd wheel. The ellipsoidal bucket has no entering lip. I cannot but believe that, of the two latter, the last is the more efficient, for the reason that the Dodd bucket is so formed that the stream is split, before entering the bucket, by the in-curved lip, while in the ellipsoidal bucket the solid stream is not split or otherwise interfered with, in any manner whatever, until after it meets the dividing-wedge.
In fact, the only contact of the ellipsoidal bucket on entering the stream is with the dividing-wedge. A lipped bucket tends to break up the stream and to deflect it during the transit of the lip, thus setting up swirling actions which interfere seriously with the reactive effect. It tends, moreover, to divert the stream outwardly, because of splitting it as by a wedge having an edge which is axial to the wheel; and thus it splits the stream transversely (see Fig. 14) before the wedge in the bucket has an opportunity to split it radially to the wheel and reverse the direction of the water. Finally, in the ellipsoidal bucket the stream is only divided in the plane of the wheel’s rotation, and thus separated into only two equal parts, each of which flows over the hydraulic-curved faces in the bucket, reversing the direction of flow without disturbance of shock, and avoiding the eddy-currents set up where an end lip is used. Buckets of the entering lip type first shave off the stream in thin slices, each slice being again divided by the central dividing-wedge, this additional disturbance to the stream preventing the smooth flow of the water through the bucket, which is essential to high efficiency.
The condition which the ideal bucket imposes, that the water shall follow along natural lines and receive an even flow throughout the whole surface of the bucket, is one which has not been satisfied by any of the forms of tangential wheels with which the engineering public is most familiar. Proof of this, as already observed, will be found in a study of buckets of those makes that have been in use for some time under high heads of water containing slickens or sand. Such buckets as those illustrated in Figs. 16 to 22 inclusive, show strongly marked erosions from whirling water within them, and demonstrate that nature often ignores entirely those paths which the designers of the buckets had selected as proper directions of discharge, and that the water takes a radically different course therefrom, as is proved by the erosion. In some cases of operation under comparatively moderate heads, this erosion is so great in the best known type of bucket as to perforate the bucket in from six weeks to two months, requiring new buckets throughout the wheel. One of these perforated buckets is shown in Figs. 22 and 28.
An analysis of some specific instances will be of interest.
In Fig. 16 (Pelton bucket) the perforation and erosion at the junction of lip and bucket-face may be noted. In Fig. 17, a small bronze Dodd bucket has its face or outer surface so formed that, in dividing the stream approximately at right-angles to the plane of rotation, it continually strikes the stream with this outer face, as is evidenced by much wear, and a perforation which can be clearly seen thereon. Such evidence demonstrates that there is a retarding influence to the passing of the buckets into the stream, as will appear on examination of Fig. 18. If we consider this in connection with the fact that the wheel from which the bucket shown in Fig. 17 was taken contained forty such buckets and ran at about one thousand revolutions per minute, giving, therefore, forty thousand impacts or disturbances per minute to the stream, we can appreciate the fact that this continual slapping in the stream would necessarily have a tendency to seriously break it up. More than this, it deflects the stream so that much of it entirely misses the bucket in advance of the bucket entering the stream (see Fig. 14).
In Fig. 18, the inner surface of a Dodd bucket is also much eroded in such a way as to disprove the theories formerly advanced concerning the discharge of water from buckets of this type. The erosion in this case shows conclusively that the greater discharge of water was from the upper and lower corners, or the inner and outer ends of the buckets; in fact, one outer end of the bucket shown in Fig. 17 is entirely cut through, while the side of the bucket whence the discharge was supposed to have taken place shows no appreciable wear, but retains practically its original thickness. The metal is also very much worn away from the inner to the outer end of the bottom of the bucket. Fig. 21 shows the whirlpool-action of the water in a modified Dodd bucket. These erosions, and the others shown, were clearly due to violent whirlpools in the water, and demonstrate that the lower end of the bucket divides the stream into horizontal strata, so as to break up and destroy its solid condition. Instead of the bucket being acted upon by solid water, it is therefore in reality filled up with a swirling mass, which causes the loss of the best effects of reaction, and reduces the efficiency very materially. Such specimens of worn water-wheels are by no means rare. As a rule, the sides which are supposed to form the discharging- or reacting-faces show very little, if any, wear, while the bottoms and ends, and particularly the corners, show the most wear, and often complete perforation, as the effect of the eddying currents (see Fig. 18). In the Dodd bucket, shown in Fig. 19, the outer lip is much worn from striking the stream; whereas the inner surface of the lip shows no wear whatever, although directly on the other side of the wall from the preceding. The conclusion is inevitable that, had the end of this bucket been left open, the energy of the water which was wasted in wearing the outer end would have given useful effect on the reactive faces, to say nothing of the advantage that would have followed from not breaking up the stream many thousand times per minute.
It is worth noting that the builders of these wheels designed the curves and shapes of the buckets with the wheel stationary, and did not take into consideration its relative velocities and the resulting angles of the buckets to the impinging jet. This is shown by the fact that all existing drawings detailing the application of the jet to the bucket show the jet impinging in the middle of the bucket, and divided into two semi-circular sectional streams of water, flowing over the faces and discharging from the sides of the buckets. The divided water is shaded in such drawings, to indicate its semi-circular section, whereas in reality the impingement of a stream of water against a surface or inclined plane causes the water to flatten and spread. This condition not being taken into consideration, the designers overlooked the requirements of free discharge. In reality, the buckets move rapidly in relation to the stream ; but in designing the curves of the buckets they have considered the actions and reactions of the stream within the bucket to be the same as if the bucket were stationary. On the contrary, the problem of the resolution of forces of the tangential wheel changes with each and every change in the position of the bucket with reference to the stream. The first authentic record of a thorough appreciation of these variations in forces which result with each change in the position of the wheel appears in the Berry patent (1893). If it be granted, as perhaps it may be, that some of the buckets produced by well-known manufacturers are correctly designed as to impulse and reaction at one given point of impingement—say, when the axis of the stream is perpendicular to the plane of the base of the bucket— then it unquestionably follows, from the equally indisputable fact that this angle and the bucket-curves are constantly changing during the period of contact between stream and bucket, that the design of the bucket, when in all other positions than that of the perpendicular stated, must vary correspondingly from a condition of slight error to one of absolute wrong. So marked is this error, that one who studies the situation in all of its many phases can but wonder that the most familiar types of tangential wheels embodying these defects in design should be possessed of a laboratory-efficiency of over 70 per cent, (which, however, they seldom realize in actual practice). The idea which prevailed in the design of the Berry bucket was, that the axis of the stream should be normal to the surface of the bucket, whatever its position within the arc of contact with the stream. To accomplish this, buckets of convex forms, of a carefully calculated curvature, were used. Just why this bucket has never seen commercial usage (unless it be that it has gone the way of many other good and useful inventions, and has been “ shelved ” by its owners) is not apparent at first; but becomes so on reflecting that, while the axis of the stream may be perpendicular to the tangent of the surface of the bucket, the stream itself, having breadth and consequently bulk, can never be such. In other words, the axis of the stream is an imaginary line without cross-section ; the stream has cross-section ; hence the line forming an outer confine to the stream, though parallel with the axis, will not be normal to the surface of the bucket. Herein rests the vital point pertaining to the Berry bucket in a commercial sense—the theory of the bucket is correct, but practically it is without distinguished utility, for the reason stated.
The theoretical feature of the Berry bucket which has been discussed, marked a distinct innovation in water-wheel practice, when its inventor declared that “ a thin edge entering the stream transversely is better than any entrance made at an angle (i.e., as in the Risdon, Pelton, Hug, Dodd, Cazin, Tutthill and Cascade buckets) or any of the forms hitherto adopted, because not only must disturbance be taken into account, but also the effect produced by the diverted water while the stream is being severed. (See Fig. 14.) The two things must be considered together; the value or effect of disturbance is much more complex than the losses due to misdirected water.” In this Mr. Berry was quite correct; but, to go a step further, it is obvious that if the transverse splitting of the stream could be avoided, that is, if the bucket could enter the jet without splitting it transversely; if the first and only splitting of the stream could be that caused by the radial dividing-wedge within the bucket; and if the curvature of this bucket could be such that the resolution of the forces exerted by the stream would always be in lines tangential to the surface of the dividing-wedge, whatever be its position in the arc of contact with the jet, then the highest possible efficiency will have been attained. These revolutionizing features are accomplished by the new form of ellipsoidal bucket, which has been brought out within the past year. The writer is therefore constrained to say that the latest and most important change and improvement in tangential water-wheel practice, since the development of the Colman-Moore-Heese buckets, has been the recent adoption of what may be called true hydraulic curves for the faces of the buckets, and the division of the jet vertically, or radially and in one plane only, after its entrance within the bucket.
The first of these features has, by some strange oversight, escaped the attention of engineers. For fifty years past it has been a prominent and even essential feature in turbine-practice, and indeed in all of the refined type of water-wheels wherein the water was reversed in its course over the faces of the buckets; but it has not been considered, or at least has not been applied, in tangential-wheel practice, up to the time when the buckets shown in Figs. 24 to 28 were adopted for wheels installed for operation in large units under high head. Previously the faces of the buckets had either been true curves, or developed curves that did not conform to the hydrodynamic conditions demanded.
As the ellipsoidal form has received United States letters- patent, passed after a crucial investigation of the subject by the officers of the bureau, I will, for explanation, quote from the descriptive portion of the Specification, merely changing Fig. numbers to conform to this article:
“ The buckets are of a double-trough form, having an elliptical contour, as shown in Fig. 24, the transverse curves at the center terminating in an acute wedge E that splits or divides the stream C into two equal parts that are diverted by this wedge, and the curves at its sides each way into the troughs forming the sides of the bucket. The form of the buckets in two planes is indicated in Figs. 25 and 26, the face or rim in Fig. 24 presenting ellipsoids developed from radii approximately, as shown, so that the curves traversed by the water after its impingement are the same in whatever direction it may flow after impingement.
‘‘ In my former application for letters-patent, the buckets, while the same in general construction and disposition as those herewith illustrated, were formed with straight sides and bottoms, and with true curves only, so the water preserved during its flow over such surfaces a uniform velocity. Subsequent experiments proved that a greater efficiency could be obtained by means of modified curves of an ellipsoidal form, as herewith illustrated, and known as the hydraulic curves for such surfaces.
“ These curves, as shown in the drawings, are generated from centers marked a, by the radii e, and are taken from practice, and one in which the axes of the ellipse from which the curves are generated are as nearly approximate as common practice admits. In other words, variations from the form shown are usually in the direction of an ellipse with greater variations between its major and minor axis, depending upon the size of the jets or streams and the size of the buckets in relation thereto.
“This ellipsoidal form of the acting surfaces which guide the flow of water in the buckets produces, as will be seen, a cumulative degree of deflection until the direction of flow is reversed—maintaining the velocity of the water with the least retardation and thus securing the maximum reactive effect, avoiding irregular flow and gaining a complete clearance of the water from the bucket after its energy is expended, also permitting a greater velocity of the wheel-rim in proportion to the head or pressure of the water and increasing the efficiency developed by the wheel.
“The dividing-wedge E is not external to, but within the bucket, and has in the rear, or from its point of entrance F, an upward or retarding angle G, so the point F, or extreme of the wedge, enters the jet or stream C in a manner to avoid disturbance of the water which had not previously come in contact with any part of the bucket. Below or beyond the end F of the wedge E the end of the bucket is cut away, as seen in Figs. 23, 25 and 27, so the sides will not touch the impinging stream, but nevertheless furnish at each side, in proper position, the required surface for reactive discharge, which takes place approximately on the lines m n, as indicated in Fig. 27.
“ In this manner there is no division or disturbance of the stream except in the plane of the wheel’s rotation, and it is to avoid this that the ends of the buckets are cut away at the bottom, omitting the usual end wall, or other obstruction that enters and cleaves the stream transversely to the dividing-wedge E, and directs it in various and devious ways, before it is divided by this wedge E.’’
Fig. 29 shows a wheel of this type having a capacity of 1000 H. P.
The theoretical deductions respecting this ellipsoidal configuration of the bucket faces, and the cutting away of the skirts of the buckets, so that the stream of water is divided in one plane only, have been fully verified by experiments under heads from 85 to 1300 feet; and the efficiency attained is such that further research as to the shape of tangential buckets gives but little promise of better results in that direction. I am, however, of the opinion that there are other means of adding to the already high efficiency of tangential water-wheels; but experiments made thus far, although extensive, are not in a form to be presented in the present paper. They will no doubt furnish subject-matter for a future paper, dealing with conduits and the internal conditions of jets issuing under high pressure. I regret that this subject could not be brought into the required form in time to constitute a part of the present paper; but it must be remembered that hydraulic phenomena developed under high pressures are very imperfectly understood, and that, so far as dealt with in practice, the problem is mainly confined to the Pacific coast, and the usual aids and references available in other cases are wanting.
I will remark again, in conclusion, that the development of open or impulse water-wheels, like all other mechanical implements, had to pass through a period of evolution, and the results obtained are the cumulative work of many men.
Having thus considered the history and development of the tangential wheel, it will be pertinent to discuss briefly its adaptability in the engineering field. The tangential wheel is especially fitted to certain classes of work. Its extreme simplicity, together with its low first cost, coupled with the fact that modern wheels are of very high efficiency (over 80 per cent.), render it suitable for such installations as require absolute reliability. As compared with the turbine, its first cost for heads of more than 50 feet is very much smaller, and its cost of maintenance is but a fraction of that of the turbine. In addition to the fact that its initial efficiency is superior to that of the turbine, it also maintains its original high efficiency throughout its life; whereas that of the turbine constantly decreases as the wheel wears in the casing, allowing the water to pass by, instead of through, the wheel. The variation in design permissible in turbine-practice is quite limited, as regards speed and power, by reason of the excessive cost of turbines of large diameter; whereas with the tangential wheel it permits of a very wide and free scope to the designer, wheels having been made in California from 3 inches to 30 feet in diameter, and to work under heads ranging from 35 to 2100 feet, and under speeds ranging from 65 to 1150 revolutions per minute. Moreover, there have been made a number of single wheels having a capacity of not less than 1000 horse-power each.
But the tangential wheel, as a means for effecting the industrial distribution of power, is brought forward not as a rival to the existing systems, but rather as a complement to them. On the Pacific coast, in the Orient, and in Central and South America, where the available water-powers are at high head, the tangential wheel is naturally at home. Its usefulness, however, is not limited to the field where these conditions exist in nature. For certain classes of work it can advance equally strong claims, even where it is necessary to artificially produce these high pressures by the use of modern high-duty, steam pumping-engines. This may seem rather dangerous ground; but when we consider the very high duty that can be secured with modern pumping-engines, coupled with a rotary motor, which will give an efficiency exceeding 80 per cent, (including the losses in a properly-designed system of distribution), and that we can rely on getting these efficiencies even in units of small size, we may appreciate the fact that the tangential wheel can honestly make a strong demand for recognition. As an example, consider the power-distribution in a modern steel- or iron-mill, where the power required by the individual machines is in large units. The advantages to be gained by the installation of a tangential-wheel system for work of this character may be summed up as follows:
The concentration of the boilers and pumping-engines in one central pumping-plant, which would be naturally installed in the most favorable location. Modern pumps can easily be designed to pump against a pressure of 300 to 500 pounds per square inch. From this central pumping-plant the distribution would consist of pipes or mains, from which the whole system would be supplied. Return-conduits could be provided to bring the water back to the pumping-engines wherever it was desired to use it over and over again. This would remove from the mills the large engines, which are required to drive the heavy machinery, economizing the room which the engines would occupy, and saving the cost of their massive foundations—inasmuch as a water-wheel of sufficient power to replace one of these engines would occupy about the same space as the fly-wheel of the engine. Being exceedingly simple and almost indestructible, the tangential wheel would save the cost of maintenance and the annoyance of break-downs of these large engines, the service of which is much impaired by the unfavorable conditions under which they labor. Moreover, the net efficiency of the water-wheel plant would be much superior to that of independent engines, besides doing away with troublesome and inefficient steam-pipes and the separated batteries of boilers. As indicated, the tangential wheel can be built of any desired horse-power capacity; also, by making the buckets of double form, a single wheel with a double nozzle is adaptable for work requiring reversing-engines; and, what is of great importance, the reversal of these wheels can be quite sudden, because as the jet is applied to the rim of the wheel its moment of inertia in reversing will be taken up by the water, without imposing the serious strains that a fly-wheel is subjected to when reversed. By using the newer type of regulating nozzles, absolute control can be had, not only of the speed, but also of the power of these wheels; and, in addition to this, the nozzle and wheel can be so designed as to keep available a large increase of power over the normal, should it be required—as, for instance, when a “ cold heat ” is going through the rolls. With these newer combinations, the efficiency of the wheel over a very wide range of power is exceedingly high; that is, the efficiency-curve of the wheel will show exceedingly high results, even when the power called for is only a fraction of its capacity. For handling auxiliary apparatus, the wheels are much superior to the usual small engines, or even to electric motors, for the reason that the water-wheels will stand all manner of abuse and neglect; they can be controlled absolutely, reversed almost instantly, are not subject to break-downs and other annoying characteristics; and, in addition, they are less costly to install. The more extended use of hydraulic apparatus would not be an innovation in a modern mill, as I presume there is no mill of any great consequence which has not an extensive hydraulic plant used for operating reciprocating motors—that is, presses, shears, lifts, manipulators, and the controlling apparatus for Bessemer converters. It would therefore be a concentration of plant; and experiment in this line, to demonstrate thoroughly the efficiency and reliability of the proposed hydraulic system of power-distribution by tangential water-wheels, may easily be undertaken simply by connecting such wheels for operating the auxiliary apparatus referred to, with the mains of existing hydraulic systems.
Postscript
After considering the difference in design, and also in wear and erosion, of the buckets of the several types, as compared with the ellipsoidal bucket, it is of interest to note the higher efficiency in the practical results ascertained from the wheels. Relative-efficiency tests are the most reliable, and really give the best insight into the relative values of the several buckets. The most recent, and perhaps the most interesting, of such comparative tests is one recently conducted in the power-plant of the San Joaquin Electric Company, Mr. J. J. Seymour, President, of Fresno, California. This case was particularly interesting, owing to the fact that the wheels were running under a head of 1410 feet, the horse-power developed being approximately 500 H. P. per wheel, the plant having been designed to be of high class, and in fact representing the best efforts of the builders. It was comparatively new. Under working-test, the wheels had failed to give as much power as was anticipated. The water available being of limited quantity, the builders of the plant had spent some time tuning the wheels up to their highest efficiency. After they had reached their best results, another maker attempted to improve the efficiency by substituting his buckets, but without success. On one wheel, however, the original buckets were removed and ellipsoidal buckets substituted in their place, all other parts of the plant, that is, the nozzles, generators and other apparatus, being left in their previous condition. With the same quantity of water delivered through the same nozzle, the ellipsoidal buckets carried an increased load of 10½ per cent, above the best results of the builders. This was indicated on the switchboard-ammeter, which gave the increased horse-power output of the generator, secured simply by substituting the ellipsoidal for the original buckets. The changing of these buckets and the testing were done by the employees of the San Joaquin Electric Company, the makers of the ellipsoidal buckets not being represented.
A number of other teats have been made, all of which have shown an increased efficiency of from 10 to 15 per cent., depending, of course, upon the efficiency of the original wheels.