218 



THE POPULAR EDUCATOR. 



HYDROSTATICS. X. 



THE ARCHIMEDIAN SCKEW LIFTING WHEEL CHAIN PUMP 

 LIFTING PUMP COMMON PUMP FOBCE PUMP. 



ANOTHER very ingenious and elegant machine, acting on the 

 same principle as the spokes in the Persian wheel, was invented 

 by the celebrated philosopher Archimedes, and is called after 

 him the Archimedian Screw (Fi?. 32). It consists of an in- 

 clined axis, which may be turned by a winch. One end of this 

 is in the stream or reservoir from which the water has to be 

 raised, and the other over the reservoir into which it is required 



Fig. 32. 



to flow. A tube or pipe is twisted spirally round this axle, the 

 angle at which it is twisted being so arranged that as it is 

 turned by the handle the water constantly flows towards the 

 upper end. A glance at the illustration will show that the 

 portions of the spiral on the side shown all incline to the right, 

 so that the water in them flows in that direction. When used 

 in practice, instead of a tube being twisted in this way, a spiral 

 flange, like the thread of a screw, but projecting to a much 

 greater distance, is fixed on the axis and made to turn inside a 

 straight tube which it just fits. 



In this way there is much less friction of the water, and a 

 larger amount can be raised than when a twisted pipe is used. 

 A working model of this screw can, with a little ingenuity, be 

 easily constructed with a piece of flexible pipe. 



There is another machine, known as the tympan, which is 

 sometimes used to raise water, and acts on the same principle, 

 though constructed differently. A hollow drum is made to turn 

 on a horizontal axis, motion being imparted to it by a wheel 

 working in the cogs round its edge. This drum is divided into 

 compartments by means of partitions curved in a similar way 

 to the spokes of the Persian wheel, and as it rotates the water 

 enters these compartments, and is emptied at the axle into 

 channels made to receive it. This, however, can only be used 

 with advantage when the water is not required to be raised to 

 a great height. 



The next machine for raising water which we shall notice is 

 the Lifting Wheel. This is an ordinary breast-wheel with the 

 floats inclined backwards ; but instead of deriving motion from 

 the water, it is turned by machinery in the opposite direction, 

 and thus raises the water into the channel above. It is, in 

 fact, a breast-wheel with the action reversed. In comparing 

 the merits of these different machines, we must consider which 

 of them causes least wasteful expenditure of power, and also 

 which is the simplest and least liable to get out of order. As 

 a rule, boo, the ^ more complicated the machine, the greater is 

 the loss from friction of the water against the sides, and from 

 opposing currents. Now, in the lifting wheel just mentioned, 

 there is a loss by leakage of the water between the floats and 

 the sides, and if a stone or piece of wood get in, there is a 

 danger of its injuring the wheel; still the machine is simple 

 in construction, and where the water has not to be raised to any 

 great height, may be used with advantage. 



Another way of making this machine is to use an over-shot 

 wheel instead of a breast-wheel. Openings are then made in 



the inside of the cylinder, and troughs placed so that the 

 buckets, when they are tilted by the revolutions of the wheel, 

 empty their contents through these openings. There are 

 usually two of these troughs, one above the other, for some of 

 the water is emptied as soon as the buckets are slightly in- 

 clined, and this flows into the 

 lower one, while, if the buckets 

 are well shaped, the greater 

 portion remains in them till 

 they reach nearly the highest 

 part of the wheel, where the 

 second trough is placed. 



In digging out foundations 

 for buildings, or in making 

 embankments to keep out 

 water, it is frequently neces- 

 sary to employ a pump of 

 some kind to remove the 

 water that accumulates, and 

 thus keep the work dry ; and 

 as there is often a large 

 amount of muddy water to be 

 removed, and many stones are 

 present, it is desirable to have 

 a machine made without valves, 

 so as not to be liable to get 

 out of repair; it should also 

 be capable of being easily 

 moved, and set up again at 

 a fresh place. Now these re- 

 quisites are best obtained by 

 means of the common chain 

 pump, which is represented in 

 the annexed figure (Fig. 33). 



Two wheels with arms ra- 

 diating like spokes are pro- rig. :j.j. 



cured. One of these, B, is 



fixed beneath the surface of the water ; the other, A, is placed 

 above the level to which it has to be pumped. This latter is 

 turned by an engine or any other motive power that is avail- 

 able. Round these wheels passes an endless chain, composed 

 of bars of iron jointed together ; to the middle of each of these 

 joints of the chain a float-board is fixed. These are all made of 

 the same size, so as to fit a vertical tube, which is placed with 

 its lower end below the surface of the water, while at the 

 upper end a spout is fixed, from which the water is conveyed 

 away. 



The wheel A is turned so that the floats ascend in the tube, 

 and it will easily be seen that as each successive board enters 

 it raises the quantity of water contained between it and the 

 board above. There is, of course, a considerable loss by leak- 

 age between the floats and the side of the tube, but practically 

 this is of little importance, and it diminishes with the speed at 

 which the pump is worked. 



Frequently the floats, instead of being fixed to the joints of 

 the chain, as shown here, are hinged to one side, and thus fall 

 flat when descending. The wheels A B may then be replaced by 

 ordinary flat sheaves. 



This pump can be made to work equally well if the tube be 

 inclined instead of being vertical, and this adds to its useful- 

 ness, as it renders it more easily applied in many cases. 



A strange modification of this is sometimes employed. Two 

 wheels are fixed as before, but instead of an endless chain with 

 floats, a flat rope, loosely woven of wool or horse-hair, passes 

 round them; flannel is also sometimes used for the pur- 

 pose. 



When this is driven rapidly it licks up, as it were, a large 

 quantity of water which forms a layer on its surface half an 

 inch or more in thickness. When it reaches the upper wheel 

 this is thrown of by centrifugal force, but it may be removed 

 at any place by letting the rope pass between rollers. This 

 pump has not come into general use, but a much larger amount 

 of water can be raised by means of it than would be supposed. 

 One of them might be seen in action a short time since at the 

 London Polytechnic, where also were working models of several 

 other hydraulic machines. 



The only other machine of the first class which we shall ex- 

 plain now is the Lifting Pump. Care must be taken not to 



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