Centrifugal Pump Impellers – Classification and Application of Each Impeller Type
As is widely known, among all industrial pump categories, centrifugal pumps are among the most recognized and widely used, owing to their ability to handle a wide variety of chemicals effectively, making them a suitable solution for many pumping and industrial fluid-handling applications.
However, operating a centrifugal pump efficiently and achieving optimal power output depends on factors related to pump selection and installation from the very beginning. One of the first questions Thái Khương receives from customers looking to purchase a centrifugal pump concerns the centrifugal pump impeller (impeller wheel) of the equipment.
This article will help you explore, together with Thái Khương, the different types of centrifugal pump impellers, their functions, and the role each plays in specific fluid pumping applications.
Understanding the Centrifugal Pump Impeller
The centrifugal pump impeller, also known as the pump wheel, is a rotating component designed to transfer energy from the pump motor to the fluid in order to move it. The impeller is constructed with vanes or channels that extend radially outward from the center of the circular wheel. When the impeller rotates, it generates centrifugal force to transport fluid from the pump casing to the discharge port.
There are many types of impellers, each with different characteristics and performance levels, offering a variety of options for specific pumping applications. Therefore, before selecting a centrifugal pump impeller, users should pay attention to the features and applications of each type.
First, let us explore the common types of centrifugal pump impellers available today and the characteristics of each
1. Open Impeller
As the name suggests, an open impeller has vanes on both sides with no shroud (protective cover). Due to the absence of a shroud, open impellers have lower power capacity and are typically installed in small pumps, operating at relatively low efficiency. Open impellers can handle a certain concentration of solid particles in the fluid, but require a high NPSH value to operate without cavitation, damage, or power loss.
Why are centrifugal pump impellers prone to cavitation? Find out in the following article here.
Open-type centrifugal pump impeller2. Semi-Open Impeller
This type of impeller is equipped with a shroud on one side (rear) to improve the mechanical efficiency of the vanes, while the other side remains open. The semi-open impeller is a design that combines features of both open and closed impellers to optimize efficiency and NPSHr values. The semi-open impeller is suitable for installation in medium-sized pumps and is capable of handling a small concentration of soft solid particles in the fluid.
Semi-open centrifugal pump impeller3. Closed Impeller
The closed impeller is similar to the semi-open impeller, but this type is equipped with shrouds on both the front and rear faces, maximizing the performance of the impeller. Closed impellers can operate at low NPSH values while still achieving high flow rate efficiency.
However, this is a type with a complex design, so the installation cost of a closed impeller is typically higher than other impeller types. A characteristic of the closed impeller is that its structure relies on wear rings with tight clearances to help reduce axial thrust and ensure the impeller consistently maintains high efficiency.
In general, the closed impeller is a commonly used centrifugal pump impeller type for large industrial pumps; however, it should only be used to pump clean fluids and chemicals, as it is highly susceptible to clogging when exposed to fluid containing solid particles.
Closed-type centrifugal pump impeller4. Vortex Impeller
Unlike the three impeller types described above, the vortex impeller is a special type with no conventional vane design. In appearance, the vortex impeller resembles a semi-open impeller, but differs in that the vortex area at the impeller center is more open and its operating function is also distinct.
The vortex impeller design is particularly suited for handling dirty fluids containing debris and fibrous solids. During operation, the vortex impeller generates a whirlpool or vacuum zone that prevents solid matter from passing through the impeller along with the pumped fluid, protecting the pump’s internal components from solid ingress.
The vortex impeller significantly reduces the risk of pump clogging and handles solid matter effectively. However, the vortex impeller only achieves low efficiency, so users should select and install this type only when handling fluids containing solid particles that match the impeller’s intended application.
Vortex-type centrifugal pump impeller5. Cutter Impeller
Like the vortex impeller, the cutter impeller is also specifically designed to handle fluids containing solid particles. However, instead of keeping solids from passing through as the vortex impeller does, the cutter impeller has sharp, hard blades that grind and wear down any solids passing through. Although it operates at low efficiency, the cutter impeller is a practical choice for pumping fluids in wastewater treatment industries, compared with other conventional impeller types that tend to clog when used in this field.
Cutter-type centrifugal pump impellerHow Does Impeller Diameter Affect Pump Performance?
As with all other types of impellers, when selecting a centrifugal pump impeller, one should also consider the impeller diameter, as it directly affects pump performance.
A larger impeller means a higher peripheral velocity at the outlet, generating greater flow rate and head. A smaller impeller will have the opposite effect. In many cases, the impeller can be trimmed in size to meet the requirements of specific applications.
Impeller diameterChecking Performance from the Characteristic Curve
In most characteristic curve drawings for centrifugal pumps, the required impeller size for pump operation is indicated. This is used to determine what impeller diameter is needed for the pump to meet the required operational performance.
Trimming the impeller to suit the application is generally less costly than using a variable frequency drive (VFD) to regulate performance. However, excessive trimming or cutting of the impeller will increase the clearance between the pump casing and the impeller, resulting in performance losses.
If you have any questions about impellers or centrifugal pump equipment, please contact Thái Khương directly. We are ready to assist, provide free consultation, and answer all your questions, as well as supply products that match your specific needs.
Thái Khương Pumps is always ready to listen and assist you.
Further reading on Centrifugal Pumps:
- When Should You Replace a Centrifugal Pump with a Screw Pump?
- When Should You Use a Multi-Stage or Single-Stage Centrifugal Pump?
- A Comprehensive Overview of Chemical Centrifugal Pumps
