We have used pumps in our homes to fill the overhead tank with water. Well, the pumps are not limited to that. In various industries like oil refineries, coal plants, chemical plants, and food processing, centrifugal pumps are used to lift oil, chemical solutions, water, soluble liquids, and many others. A mechanical device that transfers electrical energy into hydraulic energy to move fluids (slurries, liquids, or gases) is called a pump. Centrifugal pumps follow the same principle but with some advancements. The centrifugal pump uses a rotating impeller to apply centrifugal force, thereby moving fluids. This article explores the centrifugal pump working principle, types, parts, applications, and more. Centrifugal pumps are particularly suited for low-viscosity fluids. They are widely used in water treatment, chemical processing, oil refineries, and cooling systems. Engineering students must understand these systems deeply, as they form the backbone of various mechanical operations.

Let us learn the centrifugal pump definition, working principle, and parts like impeller, shaft, casing, suction & delivery pipes. We shall also study various types of centrifugal pumps based on the number of impellers, type of casing, fluid orientation, and position of the pump. The topic serves a greater purpose in your preparation for SSC JE ME and GATE ME exams. We have also made sure that you are prepared for the upcoming RRB JE Mechanical examination. Let’s start learning!

What is a Centrifugal Pump?

A centrifugal pump is a hydraulic device that uses the centrifugal force generated by the fluid to convert mechanical energy into hydraulic energy is called a centrifugal pump. It typically uses rotation to impart velocity onto a liquid, which is subsequently transformed into a flow. These pumps convert the kinetic energy of rotating objects into hydrodynamic energy and transfers them to the flowing fluid. Usually, a motor or engine provides rotational energy. They belong to the category of dynamic, axisymmetric work-absorbing turbomachinery. A real-life pump image is shown in fig 1 below.

Fig 1: Centrifugal Pump in a Coal Plant

The name centrifugal comes from the term in physics known as “Centrifugal force.” The centrifugal force in Newtonian physics is an inertial force that is directed away from an axis that is perpendicular to the axis of rotation. Let us learn about the working principle of the pumps.

The Centrifugal Pump comprises various components, and each part plays an important role in operation. The most crucial component is the impeller, which rotates at high speed to generate centrifugal force that moves the fluid. The pump casing surrounds the impeller and is designed to guide the fluid from the suction side to the discharge side while converting velocity into pressure. Centrifugal Pump bearing supports the rotating shaft. Understanding centrifugal pump parts is crucial for design, maintenance, and troubleshooting. The main components of a Centrifugal Pump are explained below.   

Fig 2: Centrifugal Pump Diagram of Parts

Impeller

The impeller is the heart of the centrifugal pump. It is a rotating disc with a curved blade attached to its surface. In the working condition, the impeller spins at high speed and transmits energy to the fluid. The impeller of a centrifugal pump helps to draw fluid from the centre. It accelerates the fluid outward due to centrifugal force. The impeller increases the fluid velocity and pressure. The impeller’s size, shape, and material affect the centrifugal pump's working principle and performance. Impellers are classified into three types provided below. 

• Open Impeller: The vanes of an open impeller are attached to a central hub, which is mounted directly to the shaft. Since no walls or covers surround the vanes, open impellers are weaker than closed ones.
• Closed Impeller: This type consists of back and front cover plates between which the vanes are usually sandwiched. These impellers have double or single inlets and are commonly installed in radial flow pumps.
• Semi-Open Impeller: A back-wall cover plate on semi-open impellers powers the van mechanically while leaving the other side open. Medium-sized pumps employ semi-open impellers.

Pump Casing

The casing of a Centrifugal Pump is the outer shell that surrounds the impeller. It acts like a chamber where kinetic energy is converted into pressure energy. It helps to collect the fluid from the impeller. Casing slows down the fluid velocity to increase the pressure and directs the fluid to the outlet. A good casing ensures that pressure is not lost at any point, maintaining the efficiency. Pump casing is broadly classified into three types provided below.

• Volute Casing: This casing has an impeller surrounding it. Such a casing offers a gradual rise in the flow area, which increases water pressure and decreases its velocity.
• Vortex Casing: A circular chamber is inserted between the casing and the impeller. The fluid generated by the impeller passes through the vortex chamber, followed by the volute casing. The vortex casing has a higher efficiency than the volute casing.
• Casing with Guide Blades: The impeller is surrounded by the blades in this casing. These blades are positioned to allow water from the impeller to enter the guide vane without shock and eventually arrive at the delivery with increased pressure.

Suction and Delivery Nozzles

The suction pipe of the Centrifugal Pump carries the fluid from he source to the pump, entering through the suction nozzle. It helps to bring the fluid to the impeller eye. The suction nozzle maintains a continuous flow for smooth operation. It must be air-tight to avoid cavitation. Correct sizing and design of the suction pipe are critical for priming. 

Shaft

Centrifugal Pump is a mechanical rod that connects the impeller to the electric motor. It rotates the impeller and transmits power. It helps to transfer the mechanical energy from the motor to the impeller. The shaft supports the rotating components inside the pump. The shaft of the Centrifugal Pump must be strong, durable and properly aligned. 

Bearing

It is used to support the shaft and allow it to spin smoothly without friction or vibration. It helps to provide support to the shaft of the Centrifugal Pump. Bearing reduces the friction and wear. It helps to maintain proper shaft alignment. If bearing is not maintained properly, then it can lead to overheating and failure of the pump. The bearing of the Centrifugal Pump is classified into two types. 

• Radial bearings – Control sideways movement.
• Thrust bearings – Handle axial (back-and-forth) forces.

Volute/Diffuser 

These are the special types of design inside the valve which is used to convert the fluid velocity into pressure. The volute of a Centrifugal Pump is a spiral casing that widens gradually, while the diffuser is a series of stationary vanes that surround the impeller. Both are designed to improve energy efficiency and reduce turbulence. 

Base Plate and Mounting Frame

These are the supporting structures of the pump assembly. It helios to holds the pump and motor piece of the Centrifugal Pump. Improper mounting can lead to misalignment, excessive vibration, and mechanical failure.

Centrifugal Pump Working Principle

The pump operates using the forced vortex flow principle or centrifugal action. The centrifugal pump transforms rotational energy, commonly from a motor, into the kinetic energy of the fluid. It indicates that when an external torque rotates a liquid mass, the rotating liquid pressure head rises. The rise in pressure head is proportional to the liquid's velocity at that position. The liquid moving through a rotating impeller generates a change in angular momentum, which increases the liquid's pressure. The casing of the Centrifugal Pump serves as the axial entry point for fluid, which is then captured in the impeller blades. The impeller installed on the primary mover shaft rotates, creating a suction lift at the impeller's eye. The impeller vanes impart kinetic energy to the water, which then departs and travels through a volute, where this energy is transformed to pressure (head). The hydraulic centre at the suction side and the water surface are separated by a pressure gradient measured by the pump's suction lift. This is negative pressure, and the atmospheric pressure outside the pump determines the maximum value it can reach. Check the working principle of the Centrifugal Pump step-by-step, with the role of each part explained in detail.

Priming (Preparation Phase)

Before the pump starts, priming is essential. This involves filling the pump vessel and suction pipe with liquid so that no air pockets remain. Since centrifugal pumps are not self-priming, any air present would prevent proper suction. Without priming, the impeller would rotate in air, and no suction would be created.

Starting the Pump (Motor Activated)

Once the motor is turned on, it rotates the shaft connected to the impeller of the centrifugal pump. The shaft is supported by beading to reduce friction. This imparts rotational energy to the impeller. The smooth rotation helps to ensure efficient energy transfer without damage. 

Fluid Enters Through the Suction Pipe

As the impeller starts rotating, a low-pressure region is created at the center (eye) of the impeller. Due to this pressure difference, the fluid is drawn into the pump through the suction pipe.

Impeller Accelerates the Fluid

When fluid enters the impeller, it gets trapped between the vanes of the rotating impeller. It is operated at high speed, which helps to gain kinetic energy and is pushed outward due to centrifugal force. The impeller of a Centrifugal Pump is the key part responsible for converting mechanical energy into kinetic energy.

Pressure Conversion in Pump Casing

As the high-velocity fluid exits the Centrifugal Pump impeller, it enters the pump casing, which is usually designed as a volute or diffuser. The casing converts the kinetic energy into pressure energy by gradually expanding the flow area.

Fluid Exits Through Delivery Pipe

Once the fluid pressure is sufficiently increased, it is directed out of the pump through the discharge nozzle and travels through the delivery pipe to its desired destination.

Continuous Operation

When the motor is running and the impeller is spinning, the above steps repeat continuously. A balance between suction pressure and centrifugal head at the outlet is maintained, ensuring smooth and uninterrupted flow.

Shutting Down the Pump

Before stopping the Centrifugal Pump, the delivery valve is closed to prevent backflow from the destination to the pump. Once the motor is turned off, rotation stops, and fluid flow ceases.

Role of Each Component in Working of Centrifugal Pump

Each part in the Centrifugal Pump performs a different function, explained in the table provided below. 

Types of Heads in Centrifugal Pumps

The highest point at which a pump can lift fluid against gravity is called the head of a pump. The head is a unit used to describe the height of a liquid column that a centrifugal pump may be able to generate as a result of the kinetic energy it imparts to the liquid. lThere are four types which are necessary while discussing pumps.

• Suction Head: The vertical height measured above the water surface in a pump from its centre line from which the water is to be pumped is called the suction head of the pump. It is denoted by ‘\(h_s\)’.
• Delivery Head: The distance measured vertically above the water surface from the centre line of the pump from which water is to be pumped is called the delivery head ‘\(h_d\)’.
• Static Head: The static head is the sum of the suction and delivery heads which is denoted by ‘H’. Mathematically, \(H = h_s + h_d\).
• Manometric Head: Theoretically, the energy given to the impeller will be equal to the manometric head of the pump. Mathematically, it is the distance through which water has to be pumped by a centrifugal pump and is denoted by ‘\(h_m\)’. 

The expression is given as, \(h_m = h_s + h_d + h_{fs} + h_{fd}\) + velocity head of water. 

Here,

• \(h_{fs}\) = Head loss due to friction in the suction pipe, in m
• \(h_{fd}\) = Head loss due to friction in the delivery pipe, in m.

3 Types of Centrifugal Pumps

Centrifugal pumps are broadly classified based on the direction of fluid flow through the impeller. The 3 types of centrifugal pumps are radial flow, axial flow, and mixed flow pumps. Each type is designed to serve different industrial and engineering needs based on pressure and flow requirements.

Radial Flow Centrifugal Pump

In a radial flow centrifugal pump, the liquid enters teh impeller axially and exits radially. The fluid is drawn into the eye of the impeller. As the impeller spins, the fluid is pushed outward at the right angle to the shaft. Velocity increases and is converted into pressure in the casing. It is used in water supply systems, boiler feed pumps, chemical processing undsutiris and others. 

Axial Flow Centrifugal Pump

An axial flow centrifugal pump pushed the fluid in the direction parallel to the shaft. The impeller acts as a propeller. It adds energy along with same axis as the fluid flow. Axial Flow centrifugal pump is ideal for low-pressure and high-volume movement. It is used in flood control, irrigation systems, cooling water circulation and others. 

Mixed Flow Centrifugal Pump

A mixed-flow pump combines characteristics of both radial and axial pumps. Fluid is discharged at an angle (between 0° and 90°) to the shaft. It creates both axial thrust and centrifugal force. The fluid moves in a spiral path, gaining both pressure and flow velocity. It is used in cooling towers, agricultural irrigation, cooling towers and others.

Three Types of Centrifugal Pump: A Detailed Comparison

Centrifugal pumps are categorized into three main types: radial flow, axial flow, and mixed flow pumps. Radial flow pumps discharge fluid perpendicular to the shaft and are ideal for high-pressure, low-flow applications. Axial flow pumps, in contrast, move fluid parallel to the shaft, offering high flow at low pressure, suitable for flood control and circulation. Mixed flow pumps combine both principles, delivering moderate pressure and flow, perfect for industrial and agricultural use. The comparison helps aspirants to choose the right pump based on system requirements, enhancing performance and energy efficiency across various applications.

Types of Centrifugal Pumps

The study of various types of centrifugal pumps is classified based on numerous factors. Below is the classification of centrifugal pumps.

Based on the Number of Stages

There are two types of pumps under this category.

Single Stage Pumps

This pump has a single impeller and a maximum pressure head rise of 125 metres. Single-stage pumps have numerous advantages, including their simple construction, steady operation, high speed, lightweight, high efficiency, small volume, great flow capacity, and simple maintenance. The single impeller is intended for usage with a high flow rate and comparatively low-pressure head. The single stage pumps have their classification: Horizontal, vertical, single-, and double-suction. A schematic of this type is shown below.

Fig 3: Single Stage Pump Schematic 

Multistage Pumps

This has a first impeller that allows fluid to enter under the suction line pressure and exit at high pressure. After the fluid leaves the first stage, it enters the second, where the pressure increases even further.  In the pump casing, many impellers are linked in series to form the multistage pump as shown in the figure below. 

Fig 4: Multistage Pump Schematic

Due to their smaller impeller diameters and closer impeller clearance, these pumps are more efficient. At the end of the pump, where the fluid comes out, the pressure can be very high. Hence, when a high discharge head is required, a multistage pump is utilised.

Based on the Type of Casing

This category also has two types of pumps.

Turbine Pump

A turbine pump is essentially a centrifugal pump with a vane diffusion enclosure. The turbine pump uses a guided impeller to radially direct incoming water as shown in the schematic below. The additional component of these types of centrifugal pumps is the guide wheel, which contains several guide vanes or diffusers. 

Fig 5: Vertical Turbine Pump Schematic Diagram

A vertical turbine pump is taken for illustration of the concept. As shown, the impeller is surrounded by diffuser blades that offer a gradually expanding channel. After passing through the blade, the liquid then flows into the housing. They are utilised in clean liquid applications where low flow, high head, adaptable operation, and compact design are necessary.

Volute Pump

The volute casing completely encloses the impeller in a volute pump. It is constructed so that fluids moving at the same speed can enter the impeller and exit the pump. It passes the fluid that the impeller is pumping while maintaining a constant flow rate through the diffuser. 

Fig 6: Volute Pump Schematic Diagram

The volute pump has a low energy loss rate. The volute casing controls the flow of this highly kinetic liquid as it discharges from the impeller. This type has two classifications as shown in the above figure: Single Volute and Double Volute.

Based on the Flow of Fluid

This is a common classification of pumps that are widely used. There are three types.

Radial Flow Pump

Now, radial pumps have an impeller that displaces fluid after turning 90 degrees to the suction. In this category, centrifugal pumps are widely used. The fluid is drawn in via the horizontal suction flange, and it is expelled via the vertical outflow flange.

Fig 7: Radial Flow Pump

It will discharge perpendicular to the shaft of the pump. When there is a flow restriction and a requirement to increase the discharge pressure, this design is frequently utilised. Radial design is therefore a high-pressure pump with a low flow rate. The majority of pumps used in the petrol and oil sectors are radial flow pumps.

Axial Flow Pump

The fluid flows parallel to the shaft in an axial flow pump as shown in the figure below. This process is identical to how a propellant operates. When there is a large flow rate and a negligibly low-pressure head, this pump is most useful. They are frequently used in dewatering and water circulation pumps.

Fig 8: Axial Flow Pump 

Mixed Flow Pump

With a mixed flow centrifugal pump, the fluid flow combines both axial and radial characteristics. There is a compromise between radial and axial pumps. Mixed pumps function at a much higher flow rate with an increase in the head.

Fig 9: Mixed Flow Pump

Based on Position of Pump

The pumps under this category depend on the position of the shaft too. But there are only three types which are commonly known.

Horizontal Pump

This pump functions by continually pumping fluid from a suction nozzle that is positioned in the middle of the impeller. A drive motor is used by a horizontal pump to convey liquid at a higher rate.

Fig 10: Horizontal Pump 

There is always a fluid flow and hence these pumps are environmentally friendly. The performance is good compared to other pumps.

Vertical Pump

These pumps are also called deep well turbine pumps. These centrifugal pumps have a vertical axis of flow and process the guiding vanes using revolving impellers and stages of stationary bowls. The length and rotational speed of the impeller have a significant impact on the pressure head design.

Fig 11: Vertical Pump

When the volume of water being pumped by a volute centrifugal pump is less, vertical pumps are employed. Vertical pumps are more expensive to replace and more difficult to install. There are several types of vertical pumps, including in-line, barrel, vertical column, submersible, and deep well pumps.

Difference Between Centrifugal Pump and Reciprocating Pump

We understood the different types of centrifugal pumps. There is another pump that is most commonly used along with this: Reciprocating Pump. We have tried to state the common difference between centrifugal pumps and reciprocating pumps which are provided in the table below.

Priming in Centrifugal Pump

In simple terms, the process of putting liquid into the pump is called priming in centrifugal pumps. All these pumps need liquid in the casing. The impeller gets filled with vapours or air and poses difficulty in the pumping action.

Fig 12: Priming Process in Centrifugal Pumps

Most pumps are incapable of pumping this trapped air. Thus priming removed this difficulty. But the priming is done before starting the pump as the density of the air inside it is low. Without the use of a pump, liquid can pass over the original reservoir before moving down to a lower level through a bent tube called a syphon tube. 

Advantages of Centrifugal Pump

Generally, any mechanical element that is widely used has numerous advantages. Below are some of the commonly known advantages of centrifugal pumps.

1. Centrifugal pumps are relatively simple in design and easy to operate, which makes them a popular choice for many industrial applications.
2. They are capable of handling high flow rates, making them ideal for moving large volumes of fluid.
3. These pumps have few moving parts, which means they require less maintenance compared to other types of pumps.
4. Centrifugal pumps are generally efficient at converting input power into the fluid flow, making them energy-efficient.

Disadvantages of Centrifugal Pump

Below is a list of disadvantages of these pumps which is inevitable in any mechanical system that works.

1. Centrifugal pumps have a limited suction lift, which means they cannot lift fluid from depths greater than a few meters.
2. They are not capable of generating high pressure. 
3. These pumps are sensitive to changes in fluid properties such as viscosity and temperature, which can affect their performance. 
4. Centrifugal pumps can experience cavitation when operating at high flow rates, which can damage the impeller and decrease performance.
5. These pumps can be more expensive compared to other types of pumps, especially when used in applications that require high flow rates or pressure.

Effects of Cavitation in Centrifugal Pumps

We just read a point about cavitation posing a problem to the functioning of a centrifugal pump. Cavitation is a phenomenon that occurs when a liquid's static pressure falls below its vapour pressure, causing tiny vapour-filled cavities to form in the liquid. 

These spaces, sometimes known as "bubbles" or "voids," collapse under greater pressure and might produce shock waves that could harm machinery. These shock waves are powerful while they are extremely near the collapsed bubble, but as they go away from the implosion, they quickly become weaker.

Fig 13: Cavitation in Impellers

Low-pressure regions are created as a fluid accelerates past an impeller blade as it passes through a fluid. Then, when the bubbles burst, they often create shock waves in the fluid that can also harm the blades. Cavitation in pumps happens in two forms: Suction and Discharge Cavitation.

Centrifugal Pump Applications

The applications of these pumps are numerous. It is easier to picture a day with these pumps in a vast majority of the industries that run countries. We have tried to capture some of the notable centrifugal pump applications. 

1. These pumps are deployed in various buildings to pump the water supply.
2. Slurries and sewage can be pumped using these pumps.
3. They are employed in heating & cooling systems along with fire protection systems.
4. These pumps are used in beverage industries such as bottled water, juice, and other drinks. 
5. The dairy sector including buttermilk, milk, and flavoured milk industries utilises these pumps to lift milk and water from lower head to higher.
6. The centrifugal pumps are used for refrigerants and cryogenics in many industries, including manufacturing, industrial, chemical, food processing, pharmaceutical, and aerospace.
7. To treat water, such as wastewater, drinking water, swimming pool water, and boiler water, they can be employed.

Thus, we now come to the end of the discussion on centrifugal pumps. It is quite technical but learning it well increases your chances to crack the AE/JE mechanical engineering exams and GATE ME exams. Practice more to learn more through our GATE ME test series and SSC JE ME test series.

Do not miss any updates. Download the Testbook App now!