APPLIED MECHANICS. 



[TUB HYDRAULIC BAM. 



the water at their lowest level, and being filled, are 



carried op one ai Jo till they come in contact with the tide 



Flf. 191. 



of a spout fitted near the summit of the wheel. They 

 are canted over by this spout, and discharge their con- 

 tents into it, to be conveyed away for their required pur- 

 poses. The empty buckets descend on the other side, to 

 be again filled and lifted as before. Thus the force of a 

 stream having inconsiderable fall is made to lift a certain 

 quantity of water nearly the whole height of the wheel. 

 The power of the wheel is expended on lifting a con- 

 tinuous wri^ht of filled buckets up one side ; and the 

 quantity of water contained in them, as well AS the 

 height to which it is lifted, depends upon the size of the 

 floats of the wheel and the pressure of the stream upon 

 them. We may suppose a wheel 20 feet in diameter, 

 with floats 8 feet broad and 1 ft. 6 ins. deep, worked at 

 the circumferential velocity of 4 feet per second by 

 a stream flowing at the rate of 12 feet per second. 

 Subtracting 4 from 12, we get 8 feet per second as the 

 excess of velocity of the stream over that of the float of 

 the wheel ; and the pressure due to that excess is ( or 

 1 square) that of a column of water 1 foot high. The 

 area of the float is 8 X 1 i= 12 square feet ; therefore the 

 total pressure on the float is equivalent to 12 cubic feet 

 of water, and it moves at the velocity of 4 feet per 

 second, or 240 feet per minute, giving the same force as 

 240 X 12-2880 cubic feet of water moved 1 foot per 

 minute. We may deduct Jrd of this to allow for various 

 losses, thus leaving an effective power equivalent to 1920 

 cubic feet of water Lifted 1 foot high per minute, or 



.- - 96 cubic feet lifted 20 feet (the height of the 



wheel) per minute. As the wheel's circumference may 

 be taken at 60 feet moving at the rate of 120 feet per 

 minute, the wheel makes 2 revolutions per minute, and 



tig- 131 



The buckets may therefore altogether contain 48 

 cubic feet ; and if their number be 24, each may have a 

 capacity of 2 cubic feet. If we estimate the <,uant 

 water acting on the wheel as the area of the Inl multi- 

 plied by the velocity of the stream, it appears that 8 ft. 

 X H ft. x 12 ft. =144 cubic feet passes per second, or 

 144x00 = 8040 cubic feet per minute, of which 96 or ^th 

 part is lifted 20 feet high by the wheel which it moves. 



The hydraulic ram is an ingenious contrivance, by 

 which a small fall of a considerable body of water is 

 made to raise a much smaller volume of water to a 

 siderable height From a reservoir A (Fig. 132), at the 

 height of a few feet above the lower level of the stream 

 at B, a large pipe conducts the water ; this pipe has an 

 aperture D, on its upper side near to its lower end, and 

 the aperture is closed by a valve opening upwards, into 

 an air-vessel, from which a small pipe F leads to a cistern 

 at a level considerably above that of A. At the lower 

 end of tho inclined pipe there is a hinged valve E, open- 

 ing inwards, and kept open by a weight fixed on a lever 

 projecting from the valve. This weight is adjusted 

 nicely, so as to counterbalance the pressure of the water 

 on the surface of the valve E, but not greatly to exceed 

 it. When the weight opens the valve, the whole of tho 

 water in tho inclined pipe C begins to flow downwards, 

 and issue at tho opening made by the valve at K. 

 Having acquired a certain velocity, it presses with gi . 

 force on the valve, and closes it in opposition to tho 

 weight, thereby completely arresting its own flow ; but 

 the momentum of the large body of water flowing along 

 the pipe C cannot be suddenly destroyed, but must 

 expend itself somewhere. It therefore lifts the small 

 valve D with considerable force, and [tart of it flows into 

 the air-vessel and up the pipe F. The momentum being 

 thus absorbed, and the water in the pipe C having be- 

 come still, the valve E again is opened by the weight, ami 

 the operation is repeated. Thus, by the alternate op. 

 and closing of the valve E, under the quiescent and 

 moving pressures of the water, a certain portion of the 

 water is forced up the pipe F, and is prevented from 

 returning by the closing of the valve D. The object of 

 the air-vessel is to provide an elastic spring for the water 

 propelled upwards : every time that the water is injected 

 into it, tho air in its npper part is compressed into a 

 smaller space ; and being perfectly elastic, tends to re- 

 sume its former volume. It therefore exerts a pressure 

 on the water, and continues its flow along the pipe F 

 during the intervals that elapse between the succcsshe 

 discharges through the valve D. In estimating the 

 power of this apparatus to raise water, we ma\ 

 it arranged with the flow-pipe vertical instead of inclined, 

 as it is usually inade'for mnvenienee., tho principle not 

 being altered, but the details of calculation simplified bv 

 the vertical arrangement (Fig. 133). We may suppose 

 Fig. 113. 



>> minute lift* the contents of all its I that the height from the valve In flu- surf.ier of (ho w-itrr 

 UckeU, amounting to 9(> cubic feut as we found above. J in A is 4 foot, and tliat the area of tho \alvu K is 1 R ,.ua.,. 



