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Pumps Page

A Little Bit of History

Pumping devices have been an important way of moving fluids for thousands of years.  The Ancient Egyptians invented water wheels with buckets mounted on them to move water for irrigation.  In the 200's B.C.  Ctesibius, a Greek inventor, made a reciprocating pump for pumping water.  At about the same time, Archimedes, a Greek mathematician, invented a screw pump made of a screw rotating in a cylinder (now known as an Archimedes screw).  This type of pump was used to drain and irrigate the Nile Valley.  Force pumps, utilizing a piston-and-cylinder combination, were used in Greece to raise water from wells.  Similar air pumps operated spectacular devices in Greek temples and theaters, such as the water organ. Times may have changed but pumps still operate in the same basic way.

Every pump can add different amounts of head to the liquid it is pumping depending on the flowrate. A pump curve is the characteristic curve showing the ability of the pump to add head at different flow rates. A system curve represents the head losses due to minor losses and friction as well as the static lift in the pumping situation of interest. The point where the curves cross is the operating point of the pump in the system.  

1.Centrifugal Pumps: True centrifugal pumps were not developed until the late 1600's, when Denis Papin, a French born inventor, made one with straight vanes.  The curved vane was introduce by British inventor John G. Appold in 1851.  Centrifugal pumps are inexpensive and can handle large amounts of fluid.  They are widely used in chemical processing plants and oil refineries.
 
There are several kinds of centrifugal pumps including radial-flow, mixed-flow, and axial flow. Every centrifugal pump has two characteristics that are same; each has an impeller that forces the liquid being pumped into a rotary motion, and each has a casing, which directs the liquid to the impeller. The liquid leaves the impeller as the impeller rotates. The liquid leaves with a higher velocity and pressure than it had when it entered. There is a conversion of some of the velocity to pressure that takes place before the liquid leaves the pump; this partial conversion takes place in the pump casing. Head loss is associated with conversion and must be taken into account.

The size of the impeller and the pump casing vary greatly with the type of centrifugal pump. Centrifugal pumps are often classified by a type number known as the specific speed that varies with the shape of the impeller.

2.Electromagnetic Pumps:   These pumps are chiefly used to move liquid sodium and liquid potassium, which serve as coolants in nuclear reactors.  They consist of electrical conductors and magnetized pipes.  These conductors send current through the fluid.  The fluid is then moved by the magnetic attraction and repulsion between the fluid's magnetic field and the magnetic field of the pipes.

3.Jet Pumps:  They operate on the principle that high-velocity fluid will carry along any other fluid it passes through.  Most jet pumps need a jet of steam or water through the fluid that needs to be moved.  The jet carries the fluid with it directly into the outlet pipe and, at the same time, creates a vacuum that draws more fluid into the pump.  The amount of fluid that is carried out of most jet pumps is several times the amount of fluid that is in the jet itself.  Jet pumps can be used to raise water from wells that are deeper than 200 feet.  They are also used to create a vacuum in an enclosed area; these are referred to as high-vacuum diffusion pumps.

4.Screw Pumps: These pumps are also known as positive-displacement pumps. It is also probably the world's oldest type of pump. Recently, it has become accepted in the United States for general use in pumping wastewater. It was based on the archimedes screw principle that has a revolving shaft fitted with one, two, or three helical blades to rotate in an inclined trough and push the wastewater up the trough. This type of pump has two very evident advantages over the afore-mentioned centrifugal pumps, (1) it can pump large solids without clumping, (2) it operates at a constant speed over a wide range of flows with good efficiencies. The photo to the left is of a screw pump from the Blacksburg Wastewater Treatment Plant. Photo courtesy of Daniel Gallagher. To learn more about screw pumps, visit (insert link to screw pump page).

5.Other Pumps : Among the other types of pumps are axial-flow, rotary, and reciprocating pumps. Axial-flow pumps use a motor to direct fluid along a path that is parallel to the pump's axis. This is a straight-line path for the fluid from its entrance at the inlet pipe through the pump to the outlet pipe. These type of pumps are most often used as compressors in turbojet engines. There are several types of rotary pumps in use today. They are the most widely used positive displacement pumps. They are used to pump such viscous liquids as motor oil, syrup, and paint. There are three main types of rotary pumps including: (1) gear pumps, (2) lobe pumps, (3) sliding vane pumps. Reciprocating pumps are among the oldest types of pumps used. They consist of a piston that moves back and forth within a cylinder. Common reciprocating pumps are lift pumps, force pumps, and bicycle tire pumps. Lift pumps are used to draw water from wells. The outlet valve is on a piston, which moves up and down in the pump's cylinder. The inlet valve is at the closed end of the cylinder. An example of a lift pump can be seen in the title of this page.

This is a positive displacement pump. It's a small model and very portable. One clear pipe is inserted into a well, and water is pumped out through the other pipe. The mechanism is illustrated to the left. Initially the positive displacement pump pumps air and so a slight vaccum is created. The pumping action is due to the mechanism that is literally forcing slugs of water from the intake pipe to the outlet. Due to the forcing action of the mechanism, the pump head curve for this pump is almost flat. Photo courtesy of Daniel Gallagher.

Pumps are classified and named based on their characteristics. The following diagram, attributed to Tchobanoglous, shows the classification of pumps.

A Serious Pump Problem:

Cavitation  

To learn more about pumps visit the website of Vanton, a company that makes pumps. www.vanton.com

References:  

Burstall, Aubrey. "pumps". Academic American Encyclopedia.Danbury Connecticut: Groiler Incorporated, 1995.622-623.

Lindstrom, Marilyn: authorized use of World Book diagrams

Tchobanoglous, George. Wastewater Engineering: Collection and Pumping of Wastewater. New York: McGraw-Hill, Inc., 1981. 276-289.

Visich, Marian, Jr. "pumps". The World Book Encyclopedia. Chicago: World Book, Inc., 1997. 898-900.

Any questions or comments may be sent to kigates@vt.edu or junovak@vt.edu

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