Centrifugal pump
Centrifugal pumps work by rotating the impeller to cause the
water to move centrifugally. Before starting the pump, the pump
casing and the suction pipe must be filled with water, and then
the motor is started to drive the impeller and the water to
rotate at a high speed. The water undergoes centrifugal motion
and is thrown to the outer edge of the impeller, and flows
through the volute pump casing. The pressurized water line of
the water pump
Working Principle of Centrifugal Pumps
The following steps are taken to complete an energy conversion
by a centrifugal pump:
Fluid enters the pump suction.It
enters the rotating impeller eye. Impeller gets its energy from
a motor, engine, or turbine.
The impeller pushes fluid
outward by centrifugal force. During this process, the fluid
reaches velocity and pressure.
Fluid enters inside the
volute (sometimes with a diffuser), reducing its velocity and
increasing the pressure. It also delivers fluid into the
discharge nozzle.
Types of Centrifugal Pump
Classification of Centrifugal Pumps Based on Number of Suctions
Most centrifugal pumps are single-suction designed; however,
sometimes it is necessary to have double-suction designs.
Single Suction
In a single-suction centrifugal pump, the fluid flows into the
inlet, and the entire liquid immediately flows into the
impeller eye (the inlet of the impeller). The centrifugal
force then produces pressure as the water leaves the impeller.
Double Suction
Single-suction will not suffice when the flow rate is too
high. In this case, double suction centrifugal pumps are used.
The impeller of this pump is engineered so that fluid enters
from both sides in comparison with the single side in a normal
case.
However, the name “double suction” must not confuse
you. Even in the double suction design, there is only a single
suction and discharge flange. The difference is in the design
of the impeller and casing.
The centrifugal pumps can be
classified based on many factors such as construction, design,
application, service, and industrial standards. Therefore, one
centrifugal pump can be placed into different groups at the
same time. Another common way of classification is based on
the number of impellers applied within the pump.
According to the principle can be divided into
Radial Pumps
In radial pumps, the fluid comes out of the impeller after 90
degrees of rotation relative to the suction. The most common
centrifugal pumps are in this category. Fluid enters the
horizontal suction flange and exits through a vertical outflow
flange. So, the discharge is perpendicular to the shaft of the
pump. This design is applied when there is a flow limitation
and you want to raise discharge pressure. Therefore, radial
design is high pressure and low flow rate pump. Most pumps
utilized in the oil and gas industries fall into this
category.
Mixed Pumps
As the name implies, in a mixed flow pump, the fluid flows
mixing both radial and axial properties. So, that is a
tradeoff between axial and radial pumps. Mixed pumps operate
at high flow rates with a decent increase in the head.
Axial Pumps
In an axial flow pump, the fluid moves parallel to the shaft.
This procedure resembles the working of a propellant. The most
significant application of this pump is when there is a large
flow rate and very little pressure head. For example, they are
common in dewatering pumps and water circulation pumps.
Application field
Centrifugal pumps are considered for many of the fluid transfer
activities. Therefore, these pumps hold more preference in various
industries. The most common applications of centrifugal pumps
include pumping water, water supply, supporting fire safety
systems, and regulating hot water. Some of the areas where
centrifugal pumps are utilized are as follows:
Energy and oil industries for pumping oil, mud, slurry, and
refining purposes and power plants.
Wastewater treatment
systems, irrigation, municipal plants, flood protection
procedures, and gas systems.
The chemical and petrochemical,
food, and medicinal industries such as hydrocarbons, cellulose,
sugar distilling, and beverage production.
Aerospace and
industrial applications in refrigerants and cryogenics.
Industrial
and fire protection systems for ventilation and heating, air
conditioning, boiler feed water, pressure boosting, and fire
security sprinkler systems.
Performance specifications for centrifugal pumps
Centrifugal pump selection is defined by a few key specifications,
including flow rate, head, power, and efficiency.
Flow rate
describes the rate at which the pump can move fluid through the
system, typically expressed in gallons per minute (gpm). The rated
capacity of a pump must be matched to the flow rate required by
the application or system. Pressure is a measure of the force per
unit area of resistance the pump can handle or overcome, expressed
in bar or psi (pounds per square inch). As in all centrifugal
pumps, the pressure in axial flow pumps varies based on the pumped
fluid's specific gravity. For this reason, head is more commonly
used to define pump energy in this way.
Head is the height
above the suction inlet that a pump can lift a fluid. It is a
shortcut measurement of system resistance (pressure) which is
independent of the fluid's specific gravity, expressed as a column
height of water given in feet (ft) or meters (m).Net positive
suction head (NPSH) is the difference between the pump's inlet
stagnation pressure head and the vapor pressure head. The required
NPSH is an important parameter in preventing pump cavitation.
Output
power, also called water horsepower, is the power actually
delivered to the fluid by the pump, measured in horsepower (hp).
Input power, also called brake horsepower, is the power that must
be supplied to the pump, measured in horsepower (hp).Efficiency is
the ratio between the input power and output power. It accounts
for energy losses in the pump (friction and slip) to describes how
much of the input power does useful work.
