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.
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 gallons of air at atmospheric pressure—then: Forcing 1,000 gallons of atmospheric air into a 1,000-gallon tank will give a working pressure of 15 pounds per square inch; 2,000 gallons, 30 pounds; 3,000 gallons, 45 pounds, and so on. Therefore, a pressure of 100 pounds in a 1,000-gallon tank (42 inches by 14 feet) would require 6,600 gallons of free atmosphere, in addition to the original 1,000 gallons, and the tank would then contain 1,000 gallons of compressed air under a working pressure of 100 pounds per square inch. A one cylinder compressor 6 inches by 6 inches, operating at a speed of 200 R.P.M. would fill this tank to a working pressure of 100 pounds in about 50 minutes. One gallon of air will deliver one gallon of water at the faucet. But the air must have the same pressure as the water, and there must be no friction. Thus, one gallon of air under a working pressure of forty-five pounds, will, theoretically, deliver one gallon of water to a height of 100 feet. But it takes three gallons of free air to make one gallon of compressed air at forty-five pounds pressure. If the lift is 100 feet, then 1,000 gallons of air under a pressure of forty-five pounds will theoretically deliver 1,000 gallons of water. Practically, the air tank would have to be loaded to a very much greater pressure to secure the 1,000 gallons of water before losing the elasticity of the compressed air. If one thousand gallons of water is needed on the farm every day, then the air pump would have to work about one hour each morning. This may not be less expensive than pumping the water directly, but it offers the advantage of water fresh from the well. Pure air pumped into the well tends to keep the water from becoming stale.
Figure 121.—(1) Single-Gear Pump Jack. This type of jack is used for wells from 20 to 40 feet deep. (2) Double-Gear, or Multiple-Gear Pump Jack. This is a rather powerful jack designed for deep wells or for elevating water into a high water-tank.