As the common, or sucking pump, operates by the production of a vacuum within the working-barrel, by which the external atmospheric pressure is called into action, and forces the water of the well up the suction-pipe, it follows, that the piston, at its greatest elevation, should never exceed the height of thirty-three feet from the surface of the water in the well.
Notwithstanding the common lifting pump, is incapable of raising water from more than thirty-three feet (in practice but thirty feet) below the place where it may be fixed, yet it may be made to deliver water at almost any required height above its piston, by the application of a continued straight pipe into the top of the working-barrel a b of the preceding figure. Thus, if we suppose twenty or thirty feet more of pipe to be so added to it, since the water once raised cannot pass downwards again through the piston valve, it must continue to rise with each stroke of the pump, until at length it will flow over the top of the pipe, or through a spout inserted in any part of its side. in this case atmospheric pressure has nothing to do with the elevation of the piston, consequently it may be carried to any height that the strength of the pump, or the force employed, is capable of; but the handle k, or any other contrivance by which the pump is worked, must be fixed at the top of the additional pipe, and the piston-rod equally extended, in order that the working-barrel may be kept within the limits of atmospheric which makes apump thus arranged inappli cable to very great depths, on account of the bending of the piston-rod. Where cast-iron pipes are used, this may in a great measure be prevented, by placing small pieces, with projecting arms of sufficient length to touch the inside of the pipe at each joint of the piston-rod, or about ten or twelve feet asunder, when this pump may be used for considerable depths with advantage. In using pumps to draw muddy or sandy water, It is always advisable to set the bottom of the pump in a close wicker basket, or other strainer, because sand and small stones very soon destroy the leather and working parts of any pump ; and when pumps are used for hot liquors, which is the case in many manufactories, thick hempen canvas must be for leather, unless the valves and pis tons are made entirely of metal, which is of course preferable.
The forcing pump is generally employed in mines or in situations where it is required to draw water from great depths. Pumps of this kind act by cam. pression instead of exhaustion. Although atmo spheric pressure is not necessary to the construc tion of forcing pumps, yet it is in most cases resorted to for raising the water, in the first instance, into the body of the pump where the forcing action commences and takes place ; and when so constructed, such pumps are usually called aft andforce pernix ; and in all the machines of this description, the water may be raised to any required height, without any limit, consistent with the strength of the parts and the power at command. Forcing pumps do not differ mate rially in construction from the common pump already described ; indeed, that pump, by a mere inversion of its parts, may be made into a forcing pump ; that is to say, placing the piston below, and the stop-valve and delivering-pipe above, as shown in the subjoined figure, where h h shows the inverted working-barrel, and i the inverted piston and rod, with a valve opening upwards; k is the stop-valve placed at the top, instead of the bottom, and also opening upwards into the rising pipe 11, which may be continued to any required height ; the lower end of the working-barrel is quite open, and must stand in, and be covered with the water it has to raise, so that no suction or feed-pipe is necessay to this pump; and the piston i may be worked by a frame o o, or in any other convenient manner. After the description already given of the common lift pump it will be needless to say anything of the action of this machine, as it is presumed the figure will render it sufficiently obvious. While the lower end of the working barrel h k is immersed in water, and the piston i moves upwards and downwards, the barrel will be filled through the piston-valve at each down-stroke, and at each up stroke its contents will be expelled through the stop-valve k, into the ascending pipe 11; and whatever the diameter of this pipe may be, will its resistance will constantly be equal to the weight of a column of water of the size of the work ing-barrel, and of a height equal to the perpendicular altitude of the water in the ascending pipe ; for this pipe may be placed horizontally or obliquely, so as materially to alter its length: but it is the perpendicular height between the surface of the water to be raised, and its point of discharge, which must alone be taken into account in estimating the load upon a pump ; since increase of length without height in the pipe produces no other resistance than that of fric tion, which is easily overcome by increasing the capacity of the pipe. It may
appear that the preceding pump is applicable to every purpose and to every situa tion, such as raising water from mines and the deepest places; but this is not the case, owing to the almost imperceptibly small elasticity of water, and the effects of the vu inertia, which belongs to fluids in common with solid matter. In working the pump shown in the last figure, if we presume the pipe 11 to be full of water, that water has not sufficient elasticity to permit the barrel h hi to discharge its contents through the valve k, without putting all the water contained in 11 into motion, while, when the piston descends, that motion will be at an end. The water in 11 will therefore be in an alter nate state of rest and motion ; and if the column is long, and its quantitythe cis inertia will be very that is to say, it will require a considerable exer tion of force to get it from a state of rest into motion • and when it has once begun to move, it will have no immediate tendency to return again to rest, but might be con tinued in its motion with lees force than that which was originally employed to move it. The descent of the piston, however, allows sufficient time for all the motion that was communicated to be completely lost; and hence, in working this pump, we not only have the weight of the column to over come, but the natural inertia to combat with at every stroke. This may, in a great measure be removed, by keeping two, or what is still better, three pumps constantly at work by a triple or three-throw crank; and accordingly this expedient is generally resorted to in all small engines for throwing water to a great height, for by this means i the water is never permitted to stand still in the pipes, but a constant flow or stream is maintained. No illustration is necessary to explain to the reader the combination of three pumps worked by a triple crank, each throw giving the alternating motion to one pump of the series, at equal dis tances of time and space throughout the revolution ; but a mechanical arrangement, wherein a triple crank is employed to work one pump, containing three buckets alternating in the same working barrel, and producing the same effect as three pumps, seems to require the aid of graphic delineation ; accordingly, we annex a cut, in which the process of raising water is thus conducted ; it is the inven tion of Mr. Downton, of Blackwell, and was the subject of a patent granted to him in 1826. The figure in the margin may be called a front elevation, a portion of the working barrel or cylinder being broken away to show the buckets, &o. a is the uppermost bucket or piston, the rod of which b b is hol low, and being connected to a bent arm d, it ts thereby attached to one of the limbs of a revolving three-throw crank e. The middle bucket f has also a hollow rod g g, which, being of smaller dimensions than the former, slides freely through it, and is connected to the crank e by another bent arm h. The lower most bucket i has a solid rod k k which passes entirely through the hollow rods of the other buckets, and is attached directly to the middle of the crank. Upon each of the limbs of the crank are placed anti-friction wheels, working in elliptical slots at the upper end of each rod, by which the attrition of the rubbing surfaces is considerably reduced.