HYDRAULICS. 



a lifting-pump may be used. This is nearly 

 the same with the former; but requires 

 the piston should be forced down beneath 

 the level of the water in the well. In this 

 it is not so indespensably necessary that 

 the leather on the piston should fit so 

 close; though it is the -better for so do- 

 ing. In the lifting-pump, the whole de- 

 pends on actually raising the water from 

 the well as though it were done by means 

 of a bucket ; this occasions many to apply 

 that designation to the piston. The same 

 precautions are necessary, if the water is 

 to be passed into any pipe, as has been 

 stated regarding the debouchure of the 

 sucking-pump. 



The forcing pump has a solid piston, as 

 seen at A in fig. 10, which, after the water 

 has passed the valve at B, is pressed 

 down, and causes the fluid to pass into the 

 conducting pipe C, where there is also 

 a valve d, to prevent its return. The 

 valve at B closes as the piston descends, 

 while that at d rises, to allow its escape 

 from the main pipe. When the piston 

 rises, the water follows, as in the two for- 

 mer instances, through the lower valve 

 B, while the smaller valve at dis also clos- 

 ed by the super-incwmbent water in the 

 conduit, e, and by the attraction of the 

 piston the water rushing after it to pre- 

 vent a vacuum. In this kind of pump, the 

 piston must fit extremely close; both on 

 account of the intended attraction of the 

 fluid from below, and to prevent its 

 escape upwards, when the piston is press- 

 ed downwards. 



The whole of those inventions, which 

 raise water by alternate risings and fall- 

 ings of only one piston, are subject to the 

 inconvenience of having the water issue 

 in jerks, which, in some instances, would 

 prove highly inconvenient. To remedy 

 this, a cistern should be placed near the 

 debouchure, or spout, whence a small 

 stream would flow with much less varia- 

 tion than from the spout itself. But the 

 best mode of regulating the issue of wa- 

 ter is by aid of an air-vessel, as in a fire- 

 engine See PNEUMATICS. 



To detail all the varieties of pumps that 

 are in use would be both beyond the li- 

 mits of this work, and of no real utility to 

 the reader : we shall, therefore, enter 

 upon the description of the valves in ge- 

 neral estimation, and then proceed to give 

 a brief account of hydraulic machinery. 



The most common kind of 'valve con- 

 sists of a piece of stiff leather, such as is 

 applied for soles in shoes, and is generally 

 known by the name of pump-leather. 

 On its upper side apiece of milled lead 



is rivetted firmly, and the part where it is 

 to be fixed on the frame, or shell, of the 

 piston is grooved, for the purpose of giv- 

 ing it pliancy, that it may work up ancl 

 down, as if on a hinge. Fig. 11, shows the 

 plan ; and fig. 12, the profile of this 

 valve, which is cheap, simple, and easily 

 repaired, though it has the defect of be- 

 ing liable to choke, and of not rising high 

 enough to allow a sufficient passage for 

 the water. 



Fig. 13, shows a button-valve, which is 

 merely a piece of turned metal A, having 

 a shank, B, of about eight inches or a foot 

 in length according to the depth of the 

 block, x z. The shank passes through 

 the bar C, at the bottom of the block, 

 and is prevented from coming up too 

 high by the stud or nut o, at its bottom. 

 When the water rises, it forces up the 

 button A, and passes through the hollow- 

 in the block, of which the superior part 

 is expanded so as to fit the bottom, which, 

 being the frustrum of a cone, necessarily 

 fits close into the expanded part as the 

 water presses it, after having passed up- 

 wards in consequence of the descent of 

 the piston, which may either be solid, as 

 in a forcing-pump, or valved, as in a lift- 

 ing or a sucking-pump. This valve may 

 be applied to a piston, as well as to that 

 part of the pipe which retains the water, 

 that may be within reach of the piston's 

 action. An improvement has been made 

 to this valve, by adding a ball of some 

 weight to the bottom of the shank B, and 

 excavating the button, in order to reduce 

 its weight in proportion : this insures the 

 regular descent of the button to its seat. 



The butterfly-valve, exhibited in fig. 14, 

 varies from the two former, in having two 

 semicircular flaps appended by hinges to 

 a bar passing over the centre of the exca- 

 vated piston. This valve is peculiarly 

 eligible, because if one part should be 

 stiff and adhere to the piston, the other 

 will play with an increased effect, though 

 not equal to the action of both valves. 



The simplest valve with which we are 

 acquainted is the sphere, which is made 

 of metal, and fits into a semi-spherical 

 cavity on the top of the piston or block. 

 When the piston (if it be on that) rises, 

 the sphere falls into the socket ; but when 

 the piston is depressed, the rush of water 

 from below forces the sphere upwards. 

 The only inconvenience attendant upon 

 this valve, which is shown at fig. 15, is, 

 that its diameter, being nearly equal to 

 that of the bore, leaves a very narrow- 

 passage for the water. This, however, 

 might perhaps be obviated, by making aft 



