A pump is a machine made to raise or move liquids or gases by suction or pressure.
Pumps serve many purposes. In rural areas, hand or electric-powered pumps lift water from a well. A pump removes water from washing machines. Pumps circulate water, gasoline, and oil within an automobile engine. Large electric pumps force water to houses in the city. Oil, gasoline, and natural gas are transported hundreds of miles through pipe lines by means of pumps. The animal heart is a very important pump.
One of the earliest known pumps was the Egyptian "chain of pots." This pump obtained water from the Nile river. Romans used pumps in connection with their skill-fully-developed aqueduct and city water system.
Today, many types of pumps perform various jobs. Basically, pumps fall into three classifications: (1) suction or reciprocating pumps, including lift pumps, (2) force pumps, and (3) centrifugal pumps.
The suction pump is often found on farms. It consists of a piston which fits air-tight into a barrel or tube. On the piston, a valve opens upward. A handle is attached to a rod; and, in turn, the rod moves the piston up and down. At the bottom of the tube is another valve which also opens upward. When the handle moves the piston downward, the air in the tube is pushed out through the valve on the piston. When the piston is moved upward, gravity closes this valve and produces a partial vacuum above the water in the bottom of the tube. The water is forced upward into the tube by the pressure of the air on the surface of the water in the well. After a few strokes of the handle, the tube is filled and water flows out the spout. Since it depends on air pressure, it can lift water only to a height equal to that pressure, about thirty-two feet.
A lift pump is a variety of the common suction pump. This type of pump is placed at the bottom of a well. It relies less upon the efficiency of its suction, but relies more on mechanically lifting water.
The force pump has no valve in the piston, but rather has a valve at the spout or delivery tube. This type of pump is used in deep wells and by fire engines. It works independently of air pressure. Force pumps are usually run by electric or gasoline engines.
A mercury vapor pump uses mercury as a piston. By removing mercury from a bulb or tube, a vacuum is created. Early light bulbs had air removed from them by this type of pump.
Centrifugal pumps are employed for removing a large quantity of water or other liquid, provided the lift is not great. Generally, a centrifugal pump consists of a fanshaped impeller, or blade. Inlets lead from the pump's center to its outer edge. An outlet is located on the edge of the pump. The impeller rotates rapidly, thus pumping the water by centrifugal force to the outlet. Washing machines use centrifugal pumps to pump out water. Modern water and sewage plants use this type of pump.
