Download basics of centrifugal pumps chandrashekhar sonawane

BASICS OF
CENTRIFUGAL PUMPS
History of Pumps
Hydraulic energy (i.e. the idea of using water)
was first converted into mechanical energy in
India about 2000 years back, by passing the water
through water wheels.
Since olden times, man has been trying to
find out convenient ways of lifting water to
higher levels for purposes of water supply and
distribution, supply of water at high pressure and
for filtration. It is believed that the idea of lifting
water by centrifugal force was first given by an
Italian scientist in the end of 16th century. Since
then, continuous advancement of this pump has
brought it to a high degree of perfection, and
today the technology is used all over the world.
Definition of a pump
A pump, in general, may be defined as a machine,
when driven with an external source, lifts the
water or some other liquid from a lower level
to high level. A pump which converts kinetic
energy into pressure energy by the principle of
centrifugal force is called a centrifugal pump.
Working principle of a Centrifugal pump
Details of a centrifugal pump
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/ February 2017 / Indian Plumbing Today
CHANDRASHEKHAR SONAWANE
l Impeller that rotates exerts centrifugal
force on the liquid
l Kinetic energy is created- i.e. the liquid is
made to move at a very high velocit
l Centrifugal force throws the liquid out
l Creates low pressure at the suction eye
l This forces new liquid into the impeller
inlet
l Liquid thrown out of the impeller moves
in the volute towards the outlet
l Liquid slows down due to increasing
sectional area converting velocity
(kinetic energy) into pressure (pressure
energy)
In fluid dynamics, Bernoulli's principle states
that an increase in the speed of a fluid occurs
simultaneously with a decrease in pressure or a
decrease in the fluid's potential energy. Bernoulli's
principle can be applied to various types of fluids
flow. The simple form of Bernoulli's equation is
valid for incompressible flows (e.g. most liquid
flows and gases moving at low speeds).
Bernoulli's principle can be derived from the
principle of conservation of energy. This states
that, in a steady flow, the sum of all forms of
energy in a fluid along a streamline is the same
at all points on that streamline. This requires that
the sum of kinetic energy, potential energy and
internal energy remains constant. Bernoulli's
principle can also be derived directly from Isaac
Newton's Second Law of Motion.
The impeller in a pump rotates at a very high
speed. The fluid that leaves the vane at the edge
of the impeller has a very high velocity (i.e.
high kinetic energy). The volute of the pump is
designed so that the cross sectional area increases
along the flow of the fluid as it travels from the
impeller edge out of the pump. The increase in
area reduces the velocity and simultaneously
increases the fluid pressure which allows it to be
pumped to the required height.
c) Long coupled pumps have a separate pump
and separate motor, connected to each other
with the help of a flexible coupling. These are
generally used for flow up to 1200 m3/hr.
Types of Centrifugal pumps
Pumps can be classified as:
1) End suction pumps
2) Axially split case pumps
3) Vertical inline pumps
4) Submersible pumps
1)End suction pumps: They are also called as
Horizontal pumps, Back pull out pumps, and
Radial split casing pumps. End suction pumps are
further classified as
a) Monoblock pumps
b) Closed coupled pumps
c) Long coupled pumps
a) Monoblock pump is simpler and easy to
handle. The motor & pump are directly
coupled together and therefore base plate and
coupling alignment is not required. These
pumps are more compact compared to closed
coupled and long coupled pumps. These
pumps are available for flows up to 200 m3/hr.
Long coupled pumps
2) Axially split case pumps: An axial split casing
pump is a pump whose casing is split axially,
or whose principal joint is parallel to the shaft
centerline. The casing is split into the upper half
and lower half. An axially split casing is always a
horizontal pump. Pump internals can be rectified
by simply removing the pump top case - there is
no need to remove the motor.
MONOBLOCK pumps
b) Closed coupled pump comes with a spacer or
rigid coupling in between impeller and the
pump shaft. These pumps are generally used
for flow up to 500 m3/hr.
Closed coupled pumps
Axially split casing pumps
Vertical inline pumps
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3) Vertical inline pumps: This pump is a vertical
pump with suction and discharge connections in
line with each other. These are generally used for
high pressure applications.
4) Submersible pumps: These pumps (pump and
motor) are fully submerged in the liquid to be
pumped. There are two basic types of submersible
pumps based on the application -whether they
are used for clear water or waste water. Clear
water submersible pumps come with closed
impellers. Submersible pumps for drainage, waste
water, effluent & sewage application comes with
semi open or open impellers based on particle size
to be handled.
Selection of Centrifugal pumps
A pump is selected based on the differential
head through which it has to operate and the
flow required at the end of the terminal. The
differential head would mean the vertical height
from the water level in the storage sump to the top
most floor to which the water is pumped. Other
factors such as the liquid to be transported, the
temperature, viscosity, particle size in the liquid
will further determine the pump size.
Pump characteristic curves
The flow of centrifugal pump increases with
reduction in head. Head is always mentioned in
metre in the pump curve. The pump selection
should be such that it is operated at highest
efficiency for the required flow rate / head to save
energy.
Drainage pumps for
particle size max 12 mm
Mr. CHANDRASHEKHAR SONAWANE
is Area Manager with India
Liaison Office, Ebara Pumps
Europe SpA. He has 15 years
experience in Sales & Services
of centrifugal pumps.
Submersible pumps
for waste water, sewage
A pump is selected based on
the differential head through
which it has to operate and
the flow required at the end
of the terminal.
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/ February 2017 / Indian Plumbing Today