Common uses include water, sewage, petroleum and petrochemical pumping. The reverse function of the centrifugal pump is a water turbine converting potential energy of water pressure into mechanical rotational energy.
==History==
According to
Reti, the first machine that could be characterized as a centrifugal pump was a
mud lifting machine which appeared as early as 1475 in a treatise by the
Italian Renaissance engineer [[Francesco di Giorgio Martini]].<ref
name="Ladislao Reti 290">Ladislao Reti, “Francesco di Giorgio
(Armani) Martini's Treatise on Engineering and Its Plagiarists”, ''Technology
and Culture'', Vol. 4, No. 3. (Summer, 1963), pp. 287-298 (290)</ref>
True centrifugal pumps were not developed until the late 17th century, when
[[Denis Papin]] built one using straight vanes. The curved vane was introduced
by British inventor [[John Appold]] in 1851.
==How it works==
Like most pumps,
a centrifugal pump converts mechanical energy from a motor to energy of a
moving fluid. A portion of the energy goes into kinetic energy of the fluid
motion, and some into potential energy, represented by fluid pressure
([[Hydraulic head]]) or by lifting the fluid, against gravity, to a higher
altitude.
{{details|Centrifugal
compressor}}
The transfer of
energy from the mechanical rotation of the impeller to the motion and pressure
of the fluid is usually described in terms of [[centrifugal force]], especially
in older sources written before the modern concept of [[centrifugal force
(rotating reference frame)|centrifugal force as a fictitious force in a
rotating reference frame]] was well articulated. The concept of centrifugal force is not
actually required to describe the action of the centrifugal pump.
In the modern
centrifugal pump, most of the energy conversion is due to the outward force
that curved impeller blades impart on the fluid. Invariably, some of the energy also pushes the
fluid into a circular motion, and this circular motion can also convey some
energy and increase the pressure at the outlet.
The relationship between these mechanisms was described, using the
typical mixed concept of centrifugal force, in an 1859 article on centrifugal
pumps:<ref>
{{cite journal
| journal = The Mechanics' magazine, and
journal of engineering, agricultural machinery, manufactures and shipbuilding
| title = Professor Thomson's Centrifugal Pump
| author = James Thomson
| volume = II
| publisher = Robertson, Brooman, & Co.
| pages = 408–410
| date = Dec. 23, 1859
| url =
}}</ref>
<blockquote>
"To arrive
by a simpler method than that just given at a general idea of the mode of
action of the exterior whirlpool in improving the efficiency of the centrifugal
pump, it is only necessary to consider that the mass of water revolving in the
whirlpool chamber, round the circumference of the wheel, must necessarily exert
a centrifugal force, and that this centrifugal force may readily be supposed to
add itself to the outward force generated within the wheel; or, in other words,
to go to increase the pumping power of the wheel. The outward force generated
within the wheel is to be understood as being produced entirely by the medium
of centrifugal force if the vanes of the wheel be straight and radial; but if
they be curved, as is more commonly the case, the outward force is partly
produced through the medium of centrifugal force, and partly applied by the
vanes to the water as a radial component of the oblique pressure, which, in
consequence of their obliquity to the radius, they apply to the water as it
moves outwards along them. On this subject it is well to observe that while the
quantity of water made to pass through a given pump with curved vanes is
perfectly variable at pleasure, the smaller the quantity becomes the more
nearly will the force generated within the wheel for impelling the water
outwards become purely centrifugal force, and the more nearly will the pump
become what the name ordinarily given to it would seem to indicate—a purely
centrifugal pump. When, however, a centrifugal pump with vanes curved backwards
in such forms as are ordinarily used in well-constructed examples of the machine,
is driven at a speed considerably above that requisite merely to overcome the
pressure of the water, and cause lifting or propulsion to commence, the radial
component of the force applied to the water by the vanes will become
considerable, and the water leaving the circumference of the wheel will have a
velocity less than that of the circumference of the wheel in a degree having
some real importance in practice."
</blockquote>
The statement
"the mass of water ... must necessarily exert a centrifugal force" is
interpretable in terms of the [[reactive centrifugal force]]—the force is not
an outward force on the water, but rather an outward force exerting ''by'' the
water, on the pump housing (the ''volute'') and on the water in the outlet
pipe. The outlet pressure is a
reflection of the pressure that applies the [[centripetal force]] that curves
the path of the water to move circularly inside the pump. On the other hand, the statement that the
"outward force generated within the wheel is to be understood as being
produced entirely by the medium of centrifugal force" is best understood
in terms of centrifugal force as a [[fictional force]] in the frame of
reference of the rotating impeller; the actual forces on the water are inward,
or centripetal, since that's the direction of force need to make the water move
in circles. This force is supplied by a
pressure gradient that is set up by the rotation, where the pressure at the
outside, at the wall of the volute, can be taken as a [[reactive centrifugal
force]]. This was typical of nineteenth
and early twentieth century writings, mixing the concepts of centrifugal force
in informal descriptions of effects, such as those in the centrifugal pump.
[[File:Centrifugal
pump volute Richards 1894.png|right|thumb|John Richards's drawing of a
theoretical shape for the volute casing around the impeller, which he calls a
"mistake" due to the constriction at "a" shown in
diagram.]]
Differing
concepts and explanations of how centrifugal pumps work have long engendered
controversy and criticism. For example,
the American Expert Commission sent to the Vienna Exposition in 1873 issued a
report that included observations that "they are misnamed centrifugal,
because they do not operate by centrifugal force at all; they operate by
pressure the same as a turbine water wheel; when people understand their method
of operating we may expect much improvement." John Richards, editor of the
San Francisco-based journal ''Industry'', also downplayed the significance of
centrifugal force in his in-depth essay.<ref>
{{cite book
| title = Centrifugal pumps: an essay on their
construction and operation, and some account of the origin and development in
this and other countries
| edition =
| author = John Richards
| publisher = The Industrial Publishing
Company
| year = 1894
| pages = 40–41
| url =
http://books.google.com/books?id=013VAAAAMAAJ&pg=PA41
}}</ref>
<blockquote>
"This
extraordinary report stands printed in a Government publication, signed by men
who were, o
==Vertical centrifugal
pumps==
Vertical
centrifugal pumps are also referred to as cantilever pumps. They utilize a
unique shaft and bearing support configuration that allows the volute to hang
in the sump while the bearings are outside of the sump. This style of pump uses no [[stuffing box]]
to seal the shaft but instead utilizes a "throttle Bushing". A common application for this style of pump
is in a [[parts washer]].
==Froth pumps==
In the mineral
processing industry, or in the extraction of oilsand, froth is generated to
separate the rich minerals or bitumen from the sand and clays. Froth contains
air that tends to block conventional pumps and cause loss of prime. Over
history, industry has developed different ways to deal with this problem. One
approach consists of using vertical pumps with a tank. Another approach is to
build special pumps with an impeller capable of breaking the air bubbles. In
the pulp and paper industry holes are drilled in the impeller. Air escapes to
the back of the impeller and a special expeller discharges the air back to the
suction tank. The impeller may also feature special small vanes between the
primary vanes called split vanes or secondary vanes. Some pumps may feature a
large eye, an inducer or recirculation of pressurized froth from the pump
discharge back to the suction to break the bubbles. <ref>
{{cite book
| title = Pumping Oilsand Froth
| | author = Baha Abulnaga
| publisher = 21st International Pump Users
Symposium, Baltimore, Maryland. Published by Texas A&M University, Texas,USA
| year = 2004
| url =
http://turbolab.tamu.edu/pubs/Pump21/P21pg001.pdf
}}</ref>
==Multistage
centrifugal pumps==
A centrifugal
pump containing two or more impellers is called a multistage centrifugal pump.
The impellers may be mounted on the same shaft or on different shafts.
For higher
pressures at the outlet impellers can be connected in series.
For higher flow
output impellers can be connected in parallel.
All energy
transferred to the fluid are derived from the mechanical energy driving the
impeller.
==Energy usage==
The energy usage
in a pumping installation is determined by the flow required, the height lifted
and the length and [[Darcy friction factor formulae|friction characteristics]]
of the pipeline.
The power
required to drive a pump (<math>P_i</math>), is defined simply
using SI units by:
[[File:Centrifugal
Pump-mod.jpg|thumb|Single-stage radial-flow centrifugal pump]]
:<math>
P_i= \cfrac{\rho\
g\ H\ Q}{\eta}
</math>
where:
:<math>P_i</math>
is the input power required (W)
:<math>\rho</math>
is the fluid density (kg/m<sup>3</sup>)
:<math>g</math>
is the standard acceleration of gravity (9.80665 m/s<sup>2</sup>)
:<math>H</math>
is the energy Head added to the flow (m)
:<math>Q</math>
is the flow rate (m<sup>3</sup>/s)
:<math>\eta</math>
is the efficiency of the pump plant as a decimal
The head added by
the pump (<math>H</math>) is a sum of the static lift, the head
loss due to friction and any losses due to valves or pipe bends all expressed
in metres of fluid. Power is more commonly expressed as kilowatts
(10<sup>3</sup> W, kW) or horsepower (kW = hp*0.746). The value for
the pump efficiency, <math>\eta_{pump}</math>, may be stated for
the pump itself or as a combined efficiency of the pump and motor system.
The '''energy usage'''
is determined by multiplying the power requirement by the length of time the
pump is operating.
==Problems of
centrifugal pumps==
[[File:Open Type
Centrifugal Pump Impeller.ogv|thumb|Open Type Centrifugal Pump Impeller]]
*
[[Cavitation]]—the Net Positive Suction Head ([[NPSH]]) of the system is too
low for the selected pump
* Wear of the
[[Impeller]]—can be worsened by suspended solids
* [[Corrosion]]
inside the pump caused by the fluid properties
* Overheating due
to low flow
* Leakage along
rotating shaft
* Lack of
prime—centrifugal pumps must be filled (with the fluid to be pumped) in order
to operate
* [[Jerk
(physics)|Surge]]
==Centrifugal
pumps for solids control==
An oilfield
solids control system needs many centrifugal pumps to sit on or in mud tanks.
The types of centrifugal pumps used are sand pumps, submersible slurry pumps,
shear pumps, and charging pumps. They are defined for their different
functions, but their working principle is the same.
=== Principle of
operation ===
The impeller of
such a pump is magnetically coupled with the motor, across a separation wall
which is resistant to the fluid pumped. The motor drives a rotor carrying one
or several pairs of [[permanent magnet]]s and these drag around a second
pair(s) of permanent magnets attached to the pump impeller.
==Priming==
Most centrifugal
pumps are not self-priming. In other words, the pump casing must be filled with
liquid before the pump is started, or the pump will not be able to function. If
the pump casing becomes filled with vapors or gases, the pump impeller becomes
gas-bound and incapable of pumping. To ensure that a centrifugal pump remains
primed and does not become gas-bound, most centrifugal pumps are located below
the level of the source from which the pump is to take its suction. The same
effect can be gained by supplying liquid to the pump suction under pressure
supplied by another pump placed in the suction line.
