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A water pump is a machine used to increase the
pressure of water in order to move it from one point to another. Modern
water pumps are used throughout the world to supply water for municipal,
industrial, agricultural, and residential uses. Water pumps also are used to
move wastewater in sewage treatment plants. Modern water pumps most often
are driven by electricity, but other power sources also are used—for
example, diesel or gasoline engines. In some remote areas, such as desert
regions, solar panels may be used to supply power to small pumps.
Reciprocating Pumps
Reciprocating pumps move water by means of a piston that moves back and
forth in a cylinder with valves to help regulate the flow direction (intake
and output) of the water. As it moves in one direction, the piston expands
the room inside the cylinder and creates a partial vacuum that draws water
into the cylinder. An intake valve closes, trapping the water that was drawn
into the cylinder; then an output valve opens concurrently with the piston
reversing direction, which forces the water out at a higher pressure than
when it entered the pump. Electric-powered reciprocating pumps most often
are double-acting, meaning that the pumping action takes place on both sides
of the piston.
Rotary Pump
Rotary pumps are by far the most prevalent kind of machine-powered pump in
use today. Rotary pumps move water using a part, or parts, that move in a
circular motion. They use their rotating components in place of the piston
found in reciprocating pumps. Moreover, unlike reciprocating pumps, rotary
pumps have no valves to direct water flow. There are many varieties of
rotary pumps that are used in wide-ranging applications.*
Centrifugal Pumps
A centrifugal pump is the most common type of rotary pump. It possesses
rotating blades—called impellers—that impart energy to water as they rotate.
The action is similar to that seen in a household blender; when a blender is
filled with water and turned on, its rotating blades cause the liquid to
swirl. The impellers are housed in a casing. Water typically enters the
casing near the shaft of the spinning impeller. The blades of the impeller
are immersed in the water to be pumped. As the impeller turns, water is
swept out from near the axis of the impeller toward a peripheral outlet.
Some centrifugal pumps employ diffusers. Typically, diffusers are stationary
blades that sit outside and near the rim of the impellers. Diffusers help
smooth the outward flow of water expelled by the inner impellers, thus
increasing the efficiency of the pump. When high pressures are needed (as in
the case of a deep well, for instance) a number of impellers may be used in
series, and the diffusers following each impeller may contain guide vanes to
gradually reduce the liquid velocity. For lower-pressure pumps, the diffuser
generally is a spiral passage, known as a volute, with its cross-sectional
area increasing gradually to reduce the velocity efficiently.
Centrifugal pumps come in a variety of sizes and shapes, and are used in
applications big and small: for pumping water from a well; for irrigation;
in wastewater treatment plants; and to circulate the water in whirlpools, to
name just a few applications.
Turbine Pumps
A turbine pump is a special kind of centrifugal pump. It resembles the
turbine blade found on a modern jet engine, and has many more individual
blades than are found on conventional centrifugal impellers. Turbine pumps
are usually more expensive and more difficult to maintain than centrifugal
pumps, but have certain advantages, such as high flow rates at high
efficiency. Turbine pumps are used to pump surface waters from lakes and
reservoirs, and for irrigation; they also are employed extensively as
deep-well pumps, which sometimes extend hundreds of meters below the ground
surface.
Jet Pump
The jet pump is fundamentally different than reciprocating or rotating
pumps: namely, it has no moving parts. Jet pumps are used extensively in
both shallow and deep wells. Jet pumps employ two pipes: the usual main well
pipe that carries water up from the subsurface, and a pressure pipe. A
standard centrifugal pump operates from the surface. The output of the
centrifugal pump is split, and roughly three-fourths of the water pumped to
the surface is sent back down through the pressure pipe where the water is
pressurized by moving through a small diameter nozzle. Below ground, where
the high-pressure pipe meets the well pipe, the pressurized water enters an
enlarged chamber in the pipe. When the water moves into the chamber, the
pressure is reduced to below the surrounding area, and water from the well
is drawn upwards into the well pipe.
Shallow-Well and Deep-Well Pumps
Both centrifugal and jet pumps are used to pump water from shallow wells
(wells that are 7 meters [25 feet] or less in depth). Jet, centrifugal, and
turbine pumps are all used for deep-well applications (from just over 7
meters [25 feet] to over 100 meters [several hundred feet] deep).
Centrifugal and turbine pumps are placed deep in the well. Sometimes a
surface motor using a shaft that runs down the well to the pump turns them.
In contrast, submersible pumps have both the motor and pump below the water
level in the well, powered through an insulated wire running to the surface.
Approximately 60 percent of domestic self-supply (i.e., home) wells in the
United States use electric submersible pumps. |
