Fig. 12.
Let S be a pipe, called the suction pipe, descending into [Pg052] the well or reservoir from which the water is to be raised, and communicating with each of the steam vessels through tubes D D′, by valves A A′, which open upwards. Let F be a pipe continued from the level of the engine to whatever higher level it is intended to elevate the water. The steam vessels V V′ communicate with the force-pipe F by valves B B′, which open upwards, through the tubes E E′. Over the steam vessels and on the force-pipe is placed a small cistern C, already mentioned, which is kept filled with cold water from the force-pipe, and from the bottom of which proceeds a pipe terminated with a cock G. This is called the condensing pipe, and can be brought alternately over each steam vessel. From this cistern another pipe communicates with the feeding boiler ([fig. 11.]), by the cock M.[9]
The communication of the pipes T T′ with the boiler can be opened and closed alternately, by the regulator R ([fig. 11.]), already described.
Now suppose the steam vessels and tubes to be all filled with common atmospheric air, and that the regulator be placed so that the communication between the tube T and the boiler be opened, the communication between the other tube T′ and the boiler being closed, steam will flow into V through T. At first, while the vessel V is cold, the steam will be condensed, and will fall in drops of water on the bottom and sides of the vessel. The continued supply of steam from the boiler will at length impart such a degree of heat to the vessel V, that it will cease to condense it. Mixed with the heated air [Pg053] contained in the vessel V, it will have an elastic force greater than the atmospheric pressure, and will therefore force open the valve B, through which a mixture of air and steam will be driven until all the air in the vessel V will have passed out, and it will contain nothing but the pure vapour of water.
When this has taken place, suppose the regulator be moved so as to close the communication between the tube T and the boiler, and to stop the further supply of steam to the vessel V; and at the same time let the condensing pipe G be brought over the vessel V, and the cock opened so as to let a stream of cold water flow upon it. This will cool the vessel V, and the steam with which it is filled will be condensed and fall in a few drops of water, leaving the interior of the vessel a vacuum. The valve B will be kept closed by the atmospheric pressure. But the elastic force of the air between the valve A and the surface of the water in the well, or reservoir, will open A, so that a part of this air will rush in, and occupy the vessel V. The air in the suction pipe S, being thus allowed an increased space, will be proportionally diminished in its elastic force, and its pressure will no longer balance that of the atmosphere acting on the external surface of the water in the reservoir. This pressure will, therefore, force water up in the tube S until its weight, together with the elastic force of the air above it, balances the atmospheric pressure. When this has taken place, the water will cease to ascend.
Let us now suppose that, by shifting the regulator, the communication is opened between T and the boiler, so that steam flows again into V. The condensing cock G being removed, the vessel will be again heated as before, the air expelled, and its place filled by the steam. The condensing pipe being again allowed to play upon the vessel V, and the further supply of steam being stopped, a vacuum will be produced in V, and the atmospheric pressure will force the water through the valve A into the vessel V, which it will nearly fill, a small quantity of air, however, remaining above it.
Thus far the mechanical agency employed in elevating the water is the atmospheric pressure; and the power of steam is no further employed than in the production of a vacuum. [Pg054] But, in order to continue the elevation of the water through the force pipe F, above the level of the steam vessel, it will be necessary to use the elastic pressure of the steam. The vessel V is now nearly filled by the water which has been forced into it by the atmosphere. Let us suppose that, the regulator being shifted again, the communication between the tube T and the boiler is opened, the condensing cock removed, and that steam flows into V. At first, coming in contact with the cold surface of the water and that of the vessel, it is condensed; but the vessel is soon heated, and the water formed by the condensed steam collects in a sheet or film upon the surface of the water in V, so as to form a surface as hot as boiling water.[10] The steam then being no longer condensed, presses on the surface of the water with its elastic force; and when that pressure becomes greater than the atmospheric pressure, the valve B is forced open, and the water issuing through it, passes through E into the force-pipe F; and this is continued until the steam has forced all the water from V, and occupies its place.
The further admission of steam through T is once more stopped by moving the regulator; and the condensing pipe being again allowed to play on V, so as to condense the steam which fills it, produces a vacuum. Into this vacuum, as before, the atmospheric pressure will force the water, and fill the vessel V. The condensing pipe being then closed, and steam admitted through T, the water in V will be forced by its pressure through the valve B and tube E into F, and so the process is continued.
We have not yet noticed the other steam vessel V′, which, as far as we have described, would have remained filled with common atmospheric air, the pressure of which on the valve A′ would have prevented the water raised in the suction pipe S from passing through it. However, this is not the case; for, during the entire process which has been described in V, similar effects have been produced in V′, which we have only omitted to notice to avoid the confusion which the two processes might produce. It will be remembered, that after the steam, in the first instance, having flowed from the boiler [Pg055] through T, has blown the air out of V through B, the communication between T and the boiler is closed. Now the same motion of the regulator which closes this, opens the communication between T′ and the boiler; for the sliding plate R ([fig. 11.]) is moved from the one tube to the other, and at the same time, as we have already stated, the condensing pipe is brought to play on V. While, therefore, a vacuum is being formed in V by condensation, the steam, flowing through T′, blows out the air through B′, as already described in the other vessel V; and while the air in S is rushing up through A into V, followed by the water raised in S by the atmospheric pressure, the vessel V′ is being filled with steam, and the air is completely expelled from it.
The communication between T and the boiler is now again opened, and the communication between T′ and the boiler closed by moving the regulator R ([fig. 11.]) from the tube T to T′; at the same time the condensing pipe is removed from over V, and brought to play upon V′. While the steam once more expels the air from V through B, a vacuum is formed by condensation in V′, into which the water in S rushes through the valve A′. In the mean time V is again filled with steam. The communication between T and the boiler is now closed, and that between T′ and the boiler is opened, and the condensing pipe removed from V′, and brought to play on V. While the steam from the boiler forces the water in V′ through B′ into the force-pipe F, a vacuum is being produced in V, into which water is raised by the atmospheric pressure.