846 



HYDRAULIC MACHINERY, FOR MINES 



bucket which shall carry the water as long as it can act beneficially, tho opening or 

 mouth of the buckets shall not be so contracted as to prevent the free admission of 

 water into them, or its free egress at the bottom of the periphery. Fairbairn's rule 

 for bucket openings in wheels of high fall is nearly as 5 to 24, that is with a bucket 

 holding 24 cubic feet, the area of the water entrance should be 5 square feet. In 

 breast wheels the area should be increased to 8 square feet, or in tho proportion of 

 one to three. With these proportions tho depth of shrouding is regarded as threo 

 times the distance from the tip to the back of the bucket. 



In wheels receiving the water below the centre of the axis, a still larger opening 

 for the entrance and exit of the water is required. 



In each variety of wheel the maximum effect of tho water can only be secured by 

 making the bucket-openings sufficiently large to allow of the ready admission and 

 escape of the water within the limits of the vertical centre. 



Undershot water-wheels. In localities where the supply of water is large, and 

 tho fall comparatively low, the undershot wheel offers an obvious and cheap medium 

 for utilising the power of the current. In the year 1825 Poncelet, after an extensive 

 series of experiments found that the floats, instead of presenting a plain radial 

 surface to the impulse of the water, ought to consist of circular arcs of assignable 

 radii of curvature. Following this discovery certain practicable rules have been 

 established which may be abridged as follows: (1) Let the stream act on the 

 buckets at from 7 to 26 inches from the point where the '.water leaves the wheel 



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(2) The product of the square root of the perpendicular height in foot from the 

 surface of the water in the head-race till it meets the buckets, multiplied by 4-2, will 

 be the velocity of the skirt of the wheel in feet per second. (3) Set the sluice at tho 

 part where the water leaves it, as near the wheel as possible, with a backward in- 

 clination, and its under edge so formed as to run the wat T in the buckets at an angle 

 of 30 from a tangent to the circumference. (4) Contrac slightly the sides of the 

 cistern next the sluice-frame conducting the water to the wheel. (5) Make the sluice- 

 opening about 4 inches narrower than the wheel. (6) Make sluice and frame so 

 that the impelling water may run freely and without obstruction to the buckets. (7) 

 Tho width of wheel must not exceed width of passage for conveying the water. 



The method of setting out tho buckets of an undershot wheel, as also tho moan 

 direction of the water entering the buckets, is shown in fig. 1174. A B line of buckets 

 inclined at an angle of 1 from tho radius lino c D ; F E mean direction of the water 

 entering the buckets, the lino being at an angle of 30 with tho tangent line F o. 



Poncclefs Undershot Water-wheel. 'A. part elevation of this wheel is shown in fig. 

 1175 : a, shrouding ; b, buckets ; c, sluico-plato ; d, grooves for sluice-plate ; <?, trans- 

 Verse beams ; /, cross-binder and planking ; g, reservoir j h t floor of water-course ; , 



