The cistern in Fig. 139 is provided with a catch basin which acts as a strainer for removing leaves, etc., that would stain the water. It is made in the form of a concrete basin and partly filled with gravel. The filter in this case is formed by a depression in the cistern floor. A section of tile is placed on the floor, and around it is filled the filtering material of gravel and sand. Filters of this kind are often filled with charcoal or other materials that are expected to purify the water. They are usually inefficient because their value as absorbers of polluting agents is short-lived and unless the materials are frequently renewed they are valueless and sometimes a detriment to rapid filtration.
Fig. 139.—Cross-section of a concrete cistern, containing a sand filter.
THE HYDRAULIC RAM
In places where its use is possible, the hydraulic ram is a most convenient and inexpensive means of mechanical water supply. It is simple in construction, requires very little attention and its cost of operation is only the labor necessary to keep it in repair. Whenever a sufficient supply of water will admit of a fall of a few feet, the hydraulic ram may be used as a pump for forcing the water to a distant elevated point, where it may be utilized for all domestic purposes. The water may be used directly from the ram or stored in an elevated tank as a reserve supply; or accumulated in a pressure tank, where additional pressure is required.
The hydraulic ram has been used since 1796, when it was invented by Joseph de Montgolfier. The principle of its operation is that of the utilization of the energy of flowing water. The running water is made to give up a portion of its momentum to elevate a part of the water, and transport it to a considerable distance. If the source of supply and the fall is sufficient, almost any amount may be elevated and carried to a great distance. Large rams are sometimes used as a means of water supply for small towns. In the use of the double-acting ram, one source of water may be used to operate the ram and water from an entirely different source may be delivered. It sometimes happens that a muddy stream and a clear spring are so located, that the water of the stream can be utilized to furnish the energy for conveying the spring water to a point where it is desired for use. This is accomplished by the double-acting ram in a most efficient manner.
Single-acting Hydraulic Ram.
—Fig. 140 represents the installation of a single-acting hydraulic ram, placed to take water from a spring E, and deliver it to an elevated tank at the house on the hill.
Fig. 140.—Hydraulic ram driven by the water from a spring.