# Centrifugal Pump Construction and Working Principle

The pump which uses centrifugal force to lift water or any similar liquid to the higher head is the centrifugal pump. For lifting the water or similar liquid to the higher head this pump only increases the pressure head energy of the liquid. Also, we refer to this pump as the rotodynamic pump. Because the pump increases the head pressure of the water or its fluid consistently without any periodic fluctuation.

The rotor of a centrifugal pump consists of several vanes. The vanes are attached in the rotor body radially. Generally, the rotor has a hollow construction. So it can contain water in its body. The vanes have a certain curvature along the direction of the rotation. Due to the rotation of the rotor inside the centrifugal pump the water inside the rotor also rotates. The water inside the rotor gets a rotational motion because the rotating vanes push the water inside the rotor. In this way, the water or any other liquid inside the rotor gets rotational kinetic energy. Ultimately this rotational kinetic energy helps to lift the water. This is the reason, we call the rotor of a centrifugal pump as the impeller. Because the rotor impels or forces the water to be lifted at a higher level of the head.

## Construction of a Centrifugal Pump

The impeller is the main part of a centrifugal pump. Actually the impeller or the rotor of the centrifugal pump has a circular structure. The impeller mainly consists of a number of radially attached concentric concaved vanes. A metallic casing holds the impeller inside it. The impeller is free to rotate about its axial shaft inside that casing without any physical obstruction. We have to design the casing in such a way that it provides a gradually increasing cross-section to the pathway of the flowing water in the centrifugal pump. Such a typically designed casing of the pump is known as volute casing.

These are the only two main parts of a centrifugal pump. In addition to these two parts, there are the inlet and outlet of the pump. Here, are the basic construction of the centrifugal pump ends.

An electric motor coupled with the shaft rotates the impeller inside the volute. The inlet of the pump holds the suction pipe. Similarly, the outlet holds the delivery pipe.

## Working Principle of Centrifugal Pump

Whenever anything rotates in a circular path it tries to run away from the center of the path due to the centrifugal force. The centrifugal force acts on the body tangentially at each position of the body on the circular path.

Similarly, if we can rotate a mass of water or any other liquid it also experiences a centrifugal force. Whenever the water gets released from this rotation it will get a linear motion along the tangent of the circular rotational path.

In a centrifugal pump, we need to rotate the water coming through the inlet of the pump. But water or any other similar liquid cannot rotate like a solid body. So, to provide rotational motion in the water, we need to get the help of an impeller or rotor. The vanes of the impeller push the water inside it in the direction of rotation. Therefore the water gets a circular motion. Due to the circular motion, a centrifugal force acts on the water. As a result, the water tends to reach the periphery of the impeller. Then the water comes out from the edge of the impeller with a tangential linear motion.

This kinetic energy of the water helps to flow the water in the water flow path in the volute. Therefore it creates an upward pressure in the water column inside the delivery pipe. Consequently, the centrifugal pump delivers the water to the reservoir placed on the upper head.

#### Why do we need to fill the centrifugal pump before it first starts?

Due to the continuous rotation, the impeller creates pressure in the water inside it. The impeller creates maximum pressure when it rotates with the full of water inside it. If the impeller is not fully filled with water, or it has any water leakage, it will not be able to create the required pressure for lifting the water. This is the reason we have to fill the impeller with full of water before starting the centrifugal pump.

### Installation of Centrifugal Pump

The suction pipe is inserted below the water level or the level of the liquid to be lifted. There is a foot valve at the opening of the suction pipe inside the water. Also, we can use a stainer at the opening of the suction pipe to prevent the entry of unwanted substances.

The foot valve acts as a non-return valve which helps the water to flow in the upward direction only. That is from source to pump. We have already told that we have to fill the impeller chamber with water before starting the centrifugal pump. In doing that the nonreturn valve takes a vital role. It prevents the water to come out from the opening of the suction pipe when we fill the impeller chamber with extra water. This is because the foot valve does not open downward.

The outlet opening of the centrifugal pump is tangential with the periphery of the circular impeller. The flow area or in other words the cross-sectional area of the water flowing path is maximum at the outlet of the centrifugal pump. Due to this typical design volute, the water comes in the entry of the delivery pipe through the outlet due to the pressure created by the centrifugal force of the rotating impeller.

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