1849.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



2.1.3 



From a work entitled 'Mecaniques et Inventions approuvees par 

 I'AcacIcmie Royale des Sciences,' published at Paris in 1735, it ap- 

 pears, that previous to the commencement of the last century, 

 neither the breast nor tlie overshot water-wheels were much in use, 

 if at all known ; and at what period, and by wliom they were in- 

 troduced, is probably equally uncertain. The overshot wheel was 

 a ^reat improvement, and its introduction was an important step in 

 the perfecting of liydraulic machines; but the breast-wheel, as now 

 generally made, is a still fui-ther improvement, and is probably 

 better calculated for effective duty under the circumstances of a 

 variable supply of water, to which almost every description of 

 water-wheel is subjected. It is not the object of the present paper 

 to enter into the dates and nature of the improvements which have 

 taken place during the last and the present centuries. Suffice it to 

 observe, that the breast-wheel has taken precedence of the overshot 

 wheel, probably not so much from any advantage gained by an in- 

 crease of power, on a given fall, as from the increased facilities 

 which a wheel of this description, having a larger diameter than 

 the height of the fall, affoi'ds for the reception of the water into 

 the chamber of the bucket, and also for its final exit at the bottom. 

 Another advantage of the increased diameter is the comparative 

 ease with which the wheel overcomes the obstruction of back- 

 water. The breast-wheel is not only less injured from the effects 

 of floods, but the retarding force is overcome with greater ease, 

 and the wheel works for a longer time and to a much greater depth 

 in back-water. 



The late Dr. Robison, Professor of Natural Philosophy in the 

 University of Edinburgh, in treating of water-wheels, says, "There 

 frequently occurs a difficulty in the making of bucket-wheels, when 

 the half-taught millwright attempts to I'etain the water a long time 

 in the buckets. The water gets into them with a difficulty which 

 he cannot account for, and spills all about, even when the buckets 

 are not mo\ing away from the spout. This arises from the air, 

 which must find its way out to admit the water, but is obstructed 

 by the entering water, and occasions a great sputtering at the en- 

 try. This may be entirely prevented by making the s](out con- 

 siderably narrower than the wheel : it will leave room at the two 

 ends of the buckets for the escape of the air. This obstruction is 

 vastly greater than one would imagine; for the water drags along 

 with it a great quantity of air, as is evident in the water-blast, as 

 described by many authors." ' 



Such were the opinions of one of our first writers on mechanical 

 philosophy; but the evil has been subsequently much increased by 

 attempting to form a bucket which should carry the water down to 

 the lowest point of the fall. In these attempts, the openings be- 

 came so contracted as to prevent the free admission of the water 

 from the cistern into the buckets, and its free discharge at the bot- 

 tom of the wheel. 



In the construction of wheels for high falls, the best proportion 

 of the opening of the bucket is found to be nearly as 5 to 24; that 

 is, the contents of the bucket being 24 cubic feet, the area of the 

 opening, or entrance for the water, would be 5 square feet. In 

 breast-wheels which receive the water at the height of 10° to 12° 



above the horizontal cen- 

 tre, the ratio should be 

 nearly as 8 to 24, or as 1 

 to 3, as shown in fig. 5. 

 With these proportions, 

 the depth of the shroud- 

 ing is assumed to be about 

 three times the width of 

 the opening, or three times 

 the distance from the lip 

 to the back of the bucket, 

 as from A to B, fig. 1, the 

 opening being 5 inches, 

 and the depth of shroud 

 15 inches. 



For lower falls, or in 

 those wheels which receive 

 the water below the hori- 

 zontal centre, a larger 

 opening becomes necessary 

 for the reception of a large 

 body of water, and for its 

 final discharge, as shown in 

 fig. 4. 



In the construction of 

 water-wheels, it is requisite, in order to attain the maximum effect, 

 to have the opening of the bucket sufficiently large to allow an 



X Bobison's ' MecbaDical Fhilosopliy/ vol. ii. p. 598. 



easy entrance and an equally free escape for the water, as its re- 

 tention in the bucket must evidently be injui'ious, when carried 

 beyond the vertical centre. 



br. Robison further observes, "There is another and very seri^ 

 ous obstruction to the motion of an overshot, or bucketed wheel. 

 When it moves in back-water, it is not only resisted by the water 

 when it moves more slowly than the wheel, which is very frequently 

 the case, but it lifts a great deal in the rising buckets. In some 

 particular states of back-water, the descending bucket fills itself 

 completely with water, and in other cases it contains a very con- 

 siderable quantity, and air of common density; wliile in some rarer 

 cases it contains le-s water, with air in a condensed state. In the 

 first case, the rising bucket must come up filled with water, which 

 it cannot drop till its mouth gets out of the water. In the second 

 case, part of the water goes out before this; but the air rarefies, 

 and therefore there is still some water dragged or lifted up by the 

 wheel, by suction, as it is usually called. In the last case, there is 

 no such back-load on the rising side of the wheel, but (which is as 

 detrimental to its performance) the descending side is employed in 

 condensing air; and although this air aids the ascent of the rising 

 side, it does not aid it so much as it impedes the descending side, 

 being (by the form of the bucket) nearer to the vertical line drawn 

 thi'ough the axis."- 



These were the difficulties under which the millwrights of Dr. 

 Robison's time laboured; and the remedy which they applied (and 

 which has since been more or less continued) was to bore holes in 

 what is technically called the 'start' of the bucket. This vvas the 

 only means adopted for removing the air from the buckets of over- 

 shot wheels, in order to facilitate the admission and emission of 

 the water. In lower falls, where wheels with oi)en buckets were 

 used, or straight float-boards radiating from the centre, large open- 

 ings were made in the sole-planking, exclusive of perforations in 

 each bucket, in order to relieve them from the condensed air. The 

 improved construction of the present time is widely different, the 

 buckets being of such a shape as to admit the water at the same 

 time that the air is making its escape. 



During the early part of 1825, and the two succeeding years, two 

 iron water-wheels, each of 120-h()rse power, were constructed in 

 Manchester for Messrs. James Finlay and Co., of the Catrine 

 Works, under the auspices of the late Mr. Buchanan, and also for 

 the same company at Deanston, in Perthsliire, of which firm Mr. 

 James Smith (Deanston) was then the resident partner. Those 

 wheels are still in operation, and taking them in the aggregate, 

 they probably rank, even at the present day, as some of the most 

 powerful and the most complete hydraulic machines in the king- 

 dom. The construction of these wheels, and others for lower falls, 

 first directed the author's attention to the ingress and egress of the 

 water, and led to the improvements which have since been intro- 

 duced by him. 



The object of these modifications may be generally stated to 

 have been, for the purpose of preventing the condensation of the 

 air, and for permitting its escape, during the filling of the bucket 

 with water, as also its re-admission during the discharge of the 

 water into the lower mill-race. 



Shortly after the construction of the water-wheels for the Ca- 

 trine and Deanston Works, a breast-wheel was made and erected, 

 for Mr. Andrew Brown, of Linwood, near Paisley. In this it was 

 observed, when the wheel was loaded, and in flood-waters, that each 

 of the buckets acted as a water-blast, and forced the water and 

 spray to a height of 6 or 8 feet above 

 the orifice at which it entered. This 

 was complained of as a great defect, and 

 in order to remedy it, openings were cut 

 in the sole-plates, and small interior 

 buckets were attached to the inner sole, 

 as shown at b, //, b, fig. 2. The air in this 

 case made its escape through the open- 

 ings a, a, a, into the inner bucket, and 

 passed upwards, as is shown by tlie ar- 

 rows, through b, h, b, into the interior 

 of the wheel. By these means it will 

 be observed, that the buckets were ef- 

 fectually cleared of air whilst they were 

 filling, and that during the obstructions 

 of back-water, the same facilities were 

 afforded for its re-admission, and the 

 discharge of the water contained in the 

 rising buckets. The effect produced by 

 this alteration could scarcely be cre- 



Fig. 2. 



dited, as the wheel not only received and parted with the water 



2 RobisoD's ' Mechanical Philosophy/ vol. ii. p. 599. 



31 



