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. [Illustration: FIG. 140.--Hydraulic ram driven by the water from a spring.] In case the ram must be located at a considerable distance from the spring in order to attain the required fall, a standpipe _D_--slightly larger than the supply pipe--is used to take advantage of the full force of the water. In long pipes, the friction of the flowing water absorbs a considerable amount of the energy of flow and a standpipe, located as indicated at _D_, in the picture, will assure the full force of the flowing water in the ram. The ram is commonly placed in an underground pit as protection from freezing during cold weather, and a drain from the bottom of the pit conducts the waste water away. The supply pipe or drive pipe _B_ and delivery pipe _C_ are buried underground below the frost line as a protection from freezing. In Fig. 141 a sectional view of the ram shows all of the working parts. The air chamber _G_ is shown partly filled with water; the impetus valve _D_ is that part of the ram which checks the flow of the running water and forces a part of it through the valve _E_, at the bottom of the air chamber.