PARTS OF CENTRIFUGAL PUMP AND THEIR FUNCTION

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.

Further we will find out, in our next post,work done by the centrifugal pump on water.