Centrifugal pumps transfer energy to the fluid primarily by means of the impeller, which is the principal component causing increased pressure and flow rate by virtue of its rotational motion.
In almost all industrial projects, from power plants and refineries to HVAC systems in high-rise buildings, centrifugal pumps play the main role in fluid transportation. But what makes the operation of these pumps possible and sits at the center of all processes is a seemingly simple yet very important component: the impeller. The centrifugal pump impeller is the main element in generating pressure and flow in this type of pump. Through the rotation of the centrifugal pump impeller, the motor’s mechanical energy is converted to kinetic energy and then to pressure, and this very process enables fluid transportation within the circuit.
An example of this component can be oriented at its applications in order to see its significance. In a thermal power plant, if the centrifugal pump impeller cannot provide the required flow rate for the boiler, electricity generation efficiency directly decreases. In a refinery, incorrect selection of the centrifugal pump impeller type may result in premature corrosion and complete process shutdown. Even in cooling systems of high-rise buildings, the impeller type directly affects output pressure and uniform fluid distribution across floors.
The centrifugal pump impellers are commonly cataloged into three types- closed, semi-open, and open impellers, depending upon the fluid conditions and applications.
Definition and Function of Centrifugal Pump Impellers
A pump impeller is one of the major parts of a centrifugal pump, and its primary role is to increase the energy which is contained in a fluid and keep the fluid flowing continuously. A rotating element which by rotation pushes fluid from an inner to an outer area. Increased fluid velocity and, thus, pressure is the result of this motion.
From a mechanical point of view, the centrifugal pump impeller consists of a number of curved vanes which are attached to a central disc. The design of these vanes is for maximum efficiency under different operating conditions. Typically, an electric motor on the pump shaft supplies the energy required for impeller rotation.
In essence, the centrifugal pump impeller is responsible for converting mechanical energy to hydraulic energy. Without proper design and selection of this component, pump performance suffers from efficiency reduction, premature wear, and even complete failure. Because of this, any engineer working in the fields of fluid mechanics, facility systems or industry needs an understanding of the types of centrifugal pump impellers and what they are used for.
Classification of Centrifugal Pump Impellers
Impellers of centrifugal pumps are normally grouped into three main classes: Closed Impeller, semi-open impeller, and Open Impeller.
Comparative Analysis of Centrifugal Pump Impeller Types
| Characteristic/Impeller Type | Closed | Semi-Open | Open |
| Efficiency | High | Medium | Low |
| Solid particle tolerance | Low | Medium | High |
| Clogging probability | Low | Medium | High |
| Cleaning capability | Difficult | Acceptable | Easy |
| Precision adjustment requirement | High | Medium | Low |
| Maintenance ease | Low | Medium | High |
| Wear resistance | High | Medium | Low |
| Clean fluid applications | Ideal | Acceptable | Limited |
| Contaminated fluid applications | Unsuitable | Suitable | Ideal |
| Manufacturing and purchase cost | High | Medium | Low |
| Common applications | Power plants, food industries, HVAC | Chemical industries, agriculture, pre-treatment | Wastewater, mining, sludge and slurry |
Closed Impeller
Closed impellers consist of vanes that are attached to a completely enclosed shroud with no openings or gaps at the edges. By a design of this sort, much more energy can be transferred to the fluid with higher pump efficiency. Such an impeller is employed, ideally, in pumps intended for transporting clean and particle-free liquids, e.g., in water supply systems, ventilation systems, or process pumps in refineries.
Advantages of Closed Impellers
- High Efficiency: Due to the enclosed design, greater energy is transferred to the fluid.
- Superior Wear Resistance: These impellers exhibit greater resistance to damage, including wear caused by suspended particles in the fluid.
- Enhanced Performance at High Pressures: Due to optimal design, closed impellers are highly suitable for high-pressure fluids.
Disadvantages of Closed Impellers
- More Difficult Maintenance: Repair or replacement operations are very time consuming because of structural complexity and limited access to vanes.
- Limitations in Transporting Fluids with Large Solid Particles: Closed impellers cannot transport fluids containing coarse particles as the vanes may become blocked.
Semi-Open Impeller
The semi-open impeller is a mixture of closed and open impeller. In this impeller, the vanes are tied to a closed shroud on one side while being open on the other. With this design, the semi-open impeller can operate at relatively good efficiency, and it can transport fluid containing solid particles.
This type of impeller is employed in agricultural pumps, wastewater pumps, and industrial pumps that require handling fluids with suspended particles.
Advantages of Semi-Open Impellers
- High Flexibility: Capable of transporting fluids with fine particles while maintaining higher efficiency compared to open impellers.
- Easier Maintenance: Due to better access to vanes, repair and maintenance are simplified.
- Suitable for Dirtier Fluids: Semi-open impellers can transport fluids containing small suspended particles.
Disadvantages of Semi-Open Impellers
- Lower Efficiency than Closed Impellers: Less energy is transferred to the fluid because the semi open design.
- Potential Reduction in Service Life under Specific Conditions: The vanes may wear more rapidly if the fluid contains abrasive material.
Open Impeller
The open impeller represents one of the simplest types of centrifugal pump impellers, wherein the vanes are positioned without any surrounding shroud. The vanes are freely placed within the pump and operate through direct contact with the fluid. Open impellers are primarily used in wastewater pumps, irrigation pumps, and pumps designed for transporting fluids containing large solid particles.
Advantages of Open Impellers
- Suitable for Fluids Containing Large Particles: Open impellers can pump fluids containing coarser particles without difficulty.
- Simple and More Economical Design: Due to simpler construction, the manufacturing cost of open impellers is lower than other types.
- Very Easy Maintenance: Due to complete access to vanes, repair and maintenance of these impellers are very simple.
Disadvantages of Open Impellers
- Lower Efficiency: Due to the open design, less energy is transferred to the fluid.
- Reduced Wear Resistance: Compared to closed impellers, these impellers are more susceptible to wear.
Engineering Guide for Impeller Selection: Key to Sustainable Centrifugal Pump Performance
Multiple factors must be evaluated to ensure that the selected impeller is fully compatible with the operating conditions and the intended fluid. Generally, no single impeller type exists that represents the optimal choice under all conditions. Proper selection results from careful examination of fluid conditions, operating environment, and operational objectives.
Correct selection not only extends pump and system life but also significantly reduces energy costs, maintenance expenses, and system downtime. The following section provides a detailed and systematic examination of the most important factors:
Fluid Type (Clean, Contaminated, Corrosive, Containing Solid Particles)
The physical and chemical characteristics of the fluid constitute the primary and most important factor in impeller selection. For clean fluids with low viscosity, closed impellers represent the optimal choice. When the fluid contains suspended solid or fibrous particles (such as wastewater or industrial return water), open or semi-open impellers are preferred.
However, it is important to mention that if the fluid is corrosive, both the material and structure of the impeller are special.
Required System Efficiency
In many industrial systems, even a slight improvement of a few percentage points in pump efficiency can have a significant impact on energy consumption and operational costs.
If efficiency is the priority (such as in power plants, pressure-boosting stations, and energy recovery systems), closed impellers are recommended. In cases where medium efficiency is sufficient, and priority lies with flexibility in fluid type, semi-open impellers are more logical.
Probability of Solid Particles or Suspended Materials
Solid particles may cause clogging, corrosion, or impeller wear. Closed impellers typically perform poorly under these conditions. Open impellers, due to the open space between vanes, provide the best resistance against clogging.
Semi-open impellers provide a balance between the two when better efficiency is required than what is provided by open impellers.
Expected Pump Flow Rate and Head
Impeller design directly affects the hydraulic performance of the pump. For high flow rates and high head applications, closed impellers are often used. For applications with medium flow rates and low head, semi-open or open impellers are better choices.
Maintenance Costs and Repair Ease
Easy impeller maintenance and industrial pump repair are important in projects where system downtime is costly. Repair of open impellers is easier because of open access and simple design. Repair of closed impellers must be performed precisely using specialized tools. Semi-open or open impellers are better if the pump is installed in an area with limited access to technical personnel.
Installation Environment and System Operating Conditions
Pressure, temperature, installation height, system type (horizontal or vertical), and even spatial limitations all influence the selection of impellers. In closed systems with high pressure, closed impellers have priority due to their more stable design. Conversely, in contaminated or corrosive environments, the simple and robust design of open or semi-open impellers gains an advantage
Where can we purchase pump impellers?
Abrovan Company, in addition to manufacturing various types of industrial pumps, is also active in the sales of pump parts. You can contact the company’s phone numbers to consult with the company’s engineers before purchasing and then proceed to buy pump spare parts.