The hydraulic ram is a machine that gets its power from the momentum of running water. A ram consists of a pipe of large diameter, an air chamber and another pipe of small diameter, all connected by means of valves to encourage the flow of water in two different directions. A supply of running water with a fall of at least two feet is run through a pipe several inches in diameter reaching from above the dam to the hydraulic ram, where part of the flow enters the air chamber of the ram. Near the foot of the large pipe, or at what might be called the tailrace, is a peculiarly constructed valve that closes when running water starts to pass through it. When the large valve closes the water stops suddenly, which causes a back-pressure sufficient to lift a check-valve to admit a certain amount of water from the large supply pipe into the air-chamber of the ram. After the flow of water is checked, the foot-valve drops of its own weight, which again starts the flow of water through the large pipe, and the process is repeated a thousand or a million times, each time forcing a little water through the check-valve into the air chamber of the ram. The water is continually being forced out into the small delivery pipe in a constant stream because of the steady pressure of the imprisoned air in the air-chamber which acts as a cushion. This imprisoned air compresses after each kick and expands between kicks in a manner intended to force a more or less steady flow of water through the small pipe. The air pressure is maintained by means of a small valve that permits a little air to suck in with the supply of water. [Illustration: Figure 112.--Hydraulic Ram. The upper drawing shows how to install the ram. The lower drawing is a detail section through the center of the ram. Water flows downhill through the supply pipe. The intermittent action of the valve forces a portion of the water through another valve into the air-chamber. Air pressure forces this water out through delivery pipe. Another valve spills the waste water over into the tailrace. An automatic air-valve intermittently admits air into the air-chamber.]