HYimnSTATK'S 



confound this with tho common or traction pump, the principle 

 on whioh it works being entirely different. 



Tho month of the tube in whioh tho water is to be raised is 

 immersed some depth in the water, a valve opening upwards 

 Ui-,.,1 in it a little below the level of the water outside. 

 I A piaten with a valve also opening 



i ' npwiinN i* mil. In t-i work tln luw.-r 



y^V^ RM l' art ' *"' aml at * n "tro** forces 

 f \ | some of the water np the tube, the 



valve in whioh prevents its return 



Fig. 34 will make this more clear. 

 A B represents tho pipe in whioh the 

 water is to be raised, the valve being 

 placed at c, a little below the sur- 

 face. D is tho piston with its valve ; 

 and this is moved by tho arrangement 

 of pump-rods shown, tho part H of tho 

 pip" being bent BO as not to interfere 

 with tho motion of the rods. In the 

 figure the piston is supposed to bo 

 rising; the water therefore opens the 

 valve and rises in B. When D has 

 reached ita highest point, c closes 

 from the weight of the water above 

 it, and while the piston descends, tho 

 pressure of the external water trying 



v. -~- ~_ 7 to maintain its lovel opens the valve 



. :u. in D and allows tho tube [again to 



fill. Thus it will bo seen that at 



every stroke of the piston the quantity of water contained 

 between D when at its lowest point and c is raised in the 

 pipe. In this pump there is obviously no limit to the height 

 to which tho water can be raised other than the strength 

 of the tube and the power required. These of course 

 increase with the height, for tho power applied to the pump- 

 handlo has to support the weight of a column of water equal 

 in area to the piston, and whose height is equal to that of the 

 spout abovo the water in the well, and also that of tho pump- 

 rods. 



This kind of pump is chiefly used where tho depth from which 

 the water has to be raised is too great to admit of the use of 

 the common or suction-pump. The main disadvantages attend- 

 ing it are tho length, and therefore the weight, of the pump- 

 rods ; and also tho fact that tho valves must be situated down 

 the well, and below the surface of the water, and therefore are 

 difficult to get at when it is necessary to mako any repairs or 

 alterations. 



Sometimes this pump is constructed in a simpler way. A 

 large tube or cylinder is fixed vertically, and has at the bottom 

 a valve opening inwards through whioh 

 tho water enters. A large and heavy 

 plunger hangs loosely in this cylinder ; 

 at the collar, however, it is made to fit 

 water-tight. The pipe in which the 

 water is to be raised is also made to 

 open into the lower part of the cylin- 

 der, a valve being placed in it, as shown 

 in Fig. 35, to prevent the return of the 

 water. The plunger is suspended by a 

 chain, and when it is raised the water 

 enters the cylinder through the valve 

 at the bottom. The piston is then 

 allowed to descend by its own weight, 

 tho valve at tho bottom immediately 

 closes, and the water is forced np the 

 side pipe. When the piston again rises, 

 the valve in this pipe closes, thereby 

 preventing any reflux, and the cylinder 

 fills as before. 



If two such pumps are fixed near 

 together, the plungers being connected 



Fig. 35. 



to opposite ends of a beam turning on its centre, their weights 

 will balance each other, and thus leave only the weight of the 

 water to bo overcome by tho power. In such a caso tho primp 

 may bo worked by a man walking from end to end of the beam; 

 and as in this way his power is mainly employed in raising his 

 own weight, a largo amount of work may be accomplished, 

 especially as, owing to the simple construction of the machine, 



there is Uttle lo from Motion. Thi 

 rudo is oonstrootion, ! a 



,:. bJSJ i 



_L 







** Mpl ytij 



power, and answers Ha purpose well. 



We will now enmider the aaoond dase of manhines, or those 

 which act by the preseurs of the air. As we shall see when we 



come to treat of pneumatics, the air yr on 



with a pressure of about 1ft Ibs. per sqnate iaeb. 

 prssint be taken for granted, bot will be folly 

 shortly. By means of this pressure all the MBbiai 

 dass work. 



Now of these the most important, because by far the moat 

 commonly used, is the ordinary eaoMoo-pusop. Tb construction 

 and action of this will easily be understood by iifsfeeni to 

 Fig. 86. F is the suction-pipe, whioh paseea down into the 

 well from which the water is to be brought. This pipe is 

 usually fitted with a grating, or dee the end ie dosed, and a 

 number of small openings bored near it, so that the water ie 

 slightly strained, and stones and other bodies, whioh would in- 

 terfere with the action of the valves, are exduded. The barrel 

 D fits on to the end of the suction-pipe, a valve s opening op- 

 wards being inserted at the junction of the two. This valve 

 with its setting is known as the "lower-box," and should be made 

 BO that it can be taken out for repairs 

 without disturbing tho barrel. ! re- 

 presents the plunger or upper box ; this, 

 too, is fitted with a flap valvo, and is 

 fixed to tho piston-rod, motion being 

 communicated to it by the handle, 

 which is a bent lever of the first kind. 



When tho pump is first set to work, 

 all tho parts arc full of air, which has 

 to be removed, and as the valves are 

 not usually very accurately made, there 

 is sometimes a little difficulty in accom- 

 plishing this. A little water, however, 

 poured into the barrel makes the valves 

 close more nearly air-tight. When tho 

 piston is raised, a partial vacuum is 

 produced in r, the air pressing on the 

 water in the well forces it np into the 

 tube to supply this. Thus at each 

 stroke some of the air is expelled, till 

 at last the water rises so as to pass 

 through the valve into the barrel. The 

 pipe is then full of water, and remains 

 ao. The valve, however, must not be 

 more than about thirty feet above the 

 water in the well, or the water will not 

 rise to it. When the water has thus 

 reached the lower box, it will at the 

 next ascent of the piston rise and fill 

 the barrel of the pump ; and as the 

 piston is again depressed, the valve s will close, and the water 

 will then open the valve in the plunger and rise above it. 

 This water is by the next rise of the piston brought to the 

 level of the spout, from which it issues, while at the same tiro* 

 a fresh supply of water rises into the barrel. Thus at each 

 stroke tho quantity of water contained in the barrel between 

 the two valves is raised and issues from the spout. It i 

 clear that here, too, the weight of the whole column of 

 water in the suction-pipe has to be supported by the power 

 applied. 



Pumps of this kind were employed long before it was known 

 on what principle they acted. The explanation then given was 

 that when the piston was raised a vacuum was created, and. 

 since " Nature abhorred a vacuum," the water rushed in to fill 

 it. This explanation satisfied people for some time, but one day 

 some men were fixing a pump in an unusually deep well, and 

 found to their surprise that they could not raise the water above 

 thirty or thirty-two feet. Having tried in vain to solve the 

 difficulty, they consulted Galileo, the most celebrated philosopher 

 of tho day, who replied that " Nature only abhorred a vaeoum 

 to the height of thirty-two feet." Thin explanation, however. 

 ili.l not satisfy on<> of his pupils, named Torrioelli ; so he, and 

 afterwards Pascal, tried various experiments with different 

 li.iuMs in the place of water, and at length hit on the eorreet 

 explanation- -that it was the pressure of the external air whioh 

 caused the liquid to rine in the pump, and that therefore it wooM 



