The illustrations show the principle upon which the pump works and the most approved way of setting pumps and engines. Centrifugal pumps usually are set in dry wells a few feet above the water-table. While these pumps have a certain amount of suction, it is found that short supply pipes are much more efficient. Where water is found in abundance within from 15 to 30 feet of the surface, and the wells may be so constructed that the pull-down, or the lowering of the water while pumping is not excessive, then it is possible to lift water profitably to irrigate crops in the humid sections. Irrigation in such cases, in the East, is more in the nature of insurance against drouth. Valuable crops, such as potatoes and strawberries, may be made to yield double, or better, by supplying plenty of moisture at the critical time in crop development. It is a new proposition in eastern farming that is likely to develop in the near future. [Illustration: Figure 119.--Centrifugal Pump. This style of pump is used in many places for irrigation. It runs at high speed, which varies according to the size of the pump. It takes water at the center and discharges it at the outside of the casing.] [Illustration: Figure 120.--Air Pressure Pump. Pumping water by air pressure requires a large air container capable of resisting a pressure of 100 pounds per square inch. This illustration shows the pressure tank, engine, air-compressor, well and submerged pump.] _Air Pressure Pump._--Instead of pumping water out of the well some farmers pump air into the well to force the water out. A double compartment cylindrical tank is placed in the water in the well. These tanks are connected with the farm water distributing system to be carried in pipes to the house and to the stock stables. Air under a pressure of from 50 to 100 pounds per square inch is stored in a steel tank above ground. Small gas-pipes connect this air pressure tank with the air-chamber of the air-water tank in the well. A peculiar automatic valve regulates the air so that it enters the compartment that is filled, or partly filled, with water, and escapes from the empty one so the two compartments work together alternately. That is, the second chamber fills with water, while the first chamber is being drawn upon. Then the first chamber fills while the second is being emptied. This system will work in a well as small as eight inches in diameter, and to a depth of 140 feet. It might be made to work at a greater depth, but it seems hardly practical to do so for the reason that, after allowing for friction in the pipes, 100 pounds of air pressure is necessary to lift water 150 feet. An air tank of considerable size is needed to provide storage for sufficient air to operate the system without attention for several days. Careful engineering figures are necessary to account for the different depths of farm wells, and the various amounts of water and power required. For instance: The air tank already contains 1,000