We were discussing the pumps and basic pumping system and also we have seen the total head developed by the centrifugal pump in our previous post.
Today we will find out the important
parts of centrifugal pump and their function with the help of this post. We
will understand here the construction of a centrifugal pump that will provides
us the information about various important parts of centrifugal pump and their
function.
Parts of centrifugal pump and their function
There are following important parts of a
centrifugal pump as mentioned here.
- Rotor or Impeller
- Casing
- Suction pipe with a foot valve and a mechanical strainer
- Delivery pipe
Above parts are important components of
a centrifugal pump, now we will see each part in detail here.
Impeller
Impeller, which is also termed as rotor
of centrifugal pump, is displayed here in following figure.
There will be one
shaft of centrifugal pump which will be coupled with the shaft of electric
motor.
Impeller or rotor of centrifugal pump is
basically a circular disc mounted over the pump shaft with key assembly. Curved
blades will be mounted on this circular disc.
The center of the impeller will
be termed as impeller eye and liquid will be sucked at this impeller eye and
further liquid will move along the curved vanes of impeller in radial direction.
Sometimes impeller curved blades are
shrouded in order to avoid the leakage across the blade tips from one passage
to another passage.
Casing
The casing of a centrifugal pump will be
similar to the casing of a reaction turbine. Casing is basically an air tight
passage surrounding the impeller and will be designed in such a way that the
kinetic energy of liquid (let us say water) discharged at the outlet of the
impeller will be converted in to pressure energy before the water leaves the
casing and enters to delivery pipe.
There will be basically three types of
casing, as mentioned here, adopted.
Volute casing
Following figure indicates the volute
casing which will surround the impeller. Volute casing will be in the form of
spiral where area of flow will be increased gradually. Velocity of flow will be
reduced with increase in area of flow in volute casing. Therefore pressure of
water flowing through casing will be increased due to decrease in velocity of
flow.
In case of volute casing, there will be
formation of eddies and hence a large amount of energy will be lost here in
case of volute casing.
Vortex casing
In case of vortex casing, there will be
one circular chamber between impeller and casing. Vortex casing is displayed
here in following figure.
As we have studied above that in case of
volute casing, there will be formation of eddies and hence a large amount of
energy will be lost. But with the introduction of circular chamber in case of
vortex casing, loss of energy due to formation of eddies will be reduced up to a
considerable amount.
Therefore, efficiency of a centrifugal
pump with vortex casing will be more as compared to the efficiency of a
centrifugal pump with volute casing.
Casing with guide vanes
Depending on the requirements of static
pressure and flow rate, a diffuser ring is provided inside the casing. In such
type of casing, impeller will be surrounded by a series of guide vanes mounted
on the diffuser ring as displayed here in following figure.
These guide vanes will be static vanes
and provides a passage of diverging in nature and hence it increases the cross
sectional area in the direction of flow which will convert the kinetic energy
in to pressure energy. After these guide vanes, there will be volute
casing.
Suction Pipe
Suction pipe connects the inlet of centrifugal
pump with the sump from where water will be required to lift.
Foot valve is one type of non-return
valve, which will be opened only in one direction i.e. upward direction, will
be fitted at the bottom of suction pipe.
One mechanical strainer is also fitted at
the bottom of suction pipe in order to avoid the entry of any foreign materials
to the centrifugal pump.
Delivery Pipe
Delivery pipe connects the outlet of
centrifugal pump with the destination point.
We must note it here that suction pipe
and discharge pipe are not integral parts of centrifugal pump but without these
pipes, centrifugal pump will not be in use.
So we have seen here the various
important parts of centrifugal pump and their function too with the help of
this post.
Do
you have any suggestions? Please write in comment box.
Reference:
Fluid
mechanics, By R. K. Bansal
Image
courtesy: Google
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