By this arrangement it will be seen that, on turning the crank by the winches, the buckets alternately receive and lift the water which has passed upwards through their valves. On raising the bucket i a vacuum is effected underneath, and the water rises from the main pipe l, and fills the lower part of the cylinder; on the descent of i, the water is received above it through its valve; while i descends, f rises, so that the water fills the space between the two; on the re-action of the bucket i, more water is received into the barrel from the main, while the upper bucket a operates upon the middle one f in the same manner as fhas been described to operate upon i; thus, by the simultaneous alternating motion of the three buckets or pistons, the water is discharged in one continuous stream. Although this invention reflects credit upon the ingenuity of the inventor, we must be permitted to question its superiority over simpler machines. It will be evident that the patentee's object, (and, if we recollect rightly, it is stated so in his specification,) is to obviate the employment of an air vessel.
But in doing this he has constructed a machine quite as expensive, and has incurred a greater waste of power, owing to the friction that must take place in his concentric tubular piston-rods; besides a greater liability to derangement by the multiplicity of parts
The forcing pump is made in two forms, suited to the situation and cir-cumstances under which it has to work. The simplest construction is shown in the annexed cut. It consists of a truly-bored cylindrical working-barrel f, the top of which is quite open to admit the solid piston, which works it in a perfectly air and water-tight state, by means of the lever or handle, or any other more convenient application of power; h is the feeding-pipe, dipping into the water to be raised, as in any other pump, and this pipe may, of course, be made of any length under thirty-three feet; k is the stop-valve covering the top of the feed-pipe, and permitting water to rise into the working-barrel as the piston ascends, but not permitting it to return again; so that whenever the piston is raised by its handle, the barrel will be filled with water forced up the pipe h by atmospheric pressure; and when the piston descends again, since there is no valve in it to permit the water to pass through it, it will be forced up the lateral pipe l (opening into the bottom of the working-barrel) and through the valve m, which prevents its returning back again, so that it is constrained to find its way up the rising pipep, fixed above the valve m; and this pipe may be continued to any required height, without regard to the pressure of the atmosphere, since the ascent of the water does not depend upon its action, but upon the mechanical force that is applied to the handle to depress the piston.
While the piston rises to fill the working-barrel, the valve m will be shut, and of course all motion of the fluid in the pipe p will cease, and hence the use of the air-vessel n; for it will be seen that the pipe p is not joined on immediately above the valve m, but that it passes through the top of an air-tight copper, or other hollow vessel n, and proceeds nearly to the bottom of it. Air being a lighter fluid than water, will of course occupy the upper part of this vessel; and as soon as the action of the pump has filled it with water up to the line o o, or just above the lower end of the open pipe p, all air that is above the water will be confined, and unable to escape. If, now, the working of the piston be supposed to throw water more rapidly into the air-vessel than it can escape by the pipe p, it is evident that such confined air will be condensed into less compass than it naturally occupies, in order to make room for the water; and as the elasticity of air is constant, and increases in power with its degree of condensation without limitation, so the spring of the air in the air-vessel will become a counterpoise or equivalent for any height to which the pipe p may be carried; and although the water in the pump explained at page 357, would not admit of condensation so as to permit a fresh quantity of water to enter the ascending-pipe without putting all its contents into motion, yet the introduction of the air-vessel obviates this difficulty; for now the new quantity of water is not delivered into a former quantity of inelastic water, but into a vessel filled with air, which readily allows a change of dimensions; and while the piston is rising, and projecting no water, the previously condensed air in n has time to re-expand into its former volume, by expelling an equivalent quantity of water up the pipe pp; and thus, if the air-vessel is large enough, a constant and equable current may be maintained.
The annexed figure shows another form of the forcing pump, though this construction is generally called the lift and force pump; its formation is the same as the last-described figure, except that the piston is not solid, but is perforated, and covered by a valve opening upwards, as in the common lifting-pump; the piston-rod q likewise moves in an air-tight manner through a stuffing-box, or collar of leather, on the top of the working-barrel, which, in this case, is closed; and the lateral deliver-ing-pipe, with its air-vessel, proceeds from the upper instead of the lower part of the working-barrel. This pump not only has the stuffing-box, but three valves, instead of two, as in the last example: it is, consequently, rather more intricate and expensive in its construction, with no other advantage than that it is rather more cleanly in its working; for if the piston of the former pump is not quite water-tight, a quantity of water may flow over the open top of its working-barrel, which cannot be the case in this pump, if well made.