The principle upon which the pump operates has already been taken up in the Instruction Paper, "Mechanics." The more common forms are known as the "lift pump," the "suction pump" and a combination of the two called the "deep well pump."

Fig. 1 shows a pump of the first kind. In this pump A is the cylinder, B the plunger, C the bottom valve and D the plunger valve. When the plunger is drawn up, a vacuum is formed in the cylinder, and water flows in through C to fill it. When the plunger is forced down, valve D opens and allows the water to flow through the plunger while C remains closed. As this operation is repeated, the water is raised by the plunger at each stroke until the entire length of the pump barrel is filled, and it will then flow from the spout in an intermittent stream.

In the suction pump shown in Fig. 2, the cylinder and valves are the same, but they are placed at the top of the well and are connected with the water below by means of a pipe, as shown. When the pump is operated, a vacuum is formed in the cylinder and pipe below the plunger, and the pressure of the atmosphere upon the surface of the water forces it up the pipe and fills the chamber, after which the action becomes the same as in the case of a lift pump. The pressure of the atmosphere is approximately 15 pounds per square inch, which corresponds to the weight of a column of water 34 feet high, which is the height that the water may be raised theoretically by suction.

When the surface of the water is a greater distance than this below the point of discharge, a pump similar to that shown in Fig. 3 must be used. A is a cylinder with plunger and valves similar to those of a suction pump. The cylinder is supported in the well at some point less than 34 feet above the surface of the water; E is an air chamber connecting with the upper part of the pump cylinder, and F a discharge pipe leading from the bottom of the air chamber E. The action is as follows: water is pumped into the bottom of the air chamber, and as it rises and seals the end of the discharge pipe, the air in the upper part of the chamber is compressed, and as soon as sufficient pressure is obtained the water is forced out through the discharge pipe F. The pressure required in the air chamber depends upon the height to which the water is raised.