A pump impeller is a rotating component of a centrifugal pump that transfers energy from the motor to the fluid. It consists of a number of blades or vanes that are attached to a hub and a shaft. The impeller is usually enclosed by a casing or a volute to create a pressure difference between the inlet and the outlet of the pump.
It works by accelerating the fluid outward from the center of rotation, increasing its velocity and pressure for efficient flow. There are many types, features, and applications of pump impellers, depending on the design, shape, angle, number, and size of the blades, as well as the characteristics and requirements of the fluid and the pump.
Types of Pump Impellers
One of the main factors that determine the performance and efficiency of a pump is the type of impeller. The type of impeller affects the flow pattern, pressure, and power consumption of the fluid. There are three basic categories of centrifugal pump impellers: open, semi-open, and closed.
Open impeller
Open impellers feature vanes without surrounding shrouds or coverings, allowing the fluid to enter and exit freely.
- Simple and easy to clean
- The blades are exposed to liquid and are prone to wear and corrosion
- low efficiency
Open impellers are suitable for handling fluids with high viscosity, solids, or abrasives, such as sewage, sludge, or slurries. An example of a pump that uses an open impeller is a trash pump, which can pump water containing debris, sand, mud, etc.
Semi-open impeller
Semi-open impellers have a cover or shroud on one side of the blades, usually the backside. This configuration allows the handling of liquids with small solids or fibers while providing a balance between efficiency and resilience against clogging.
- More efficient and durable than open impellers
- Requires frequent maintenance and adjustments to prevent clogs and leaks
Semi-open impellers can handle fluids with moderate viscosity, solids, or abrasives, such as wastewater, pulp, or paper. An example of a pump that uses a semi-open impeller is a chemical pump, which can pump corrosive, toxic, or flammable liquids.
Closed impeller
A closed impeller consists of blades sandwiched between two discs with covers or shrouds on both sides to form a channel between them.
- The most efficient and stable impeller type
- The most complex and expensive to manufacture and maintain
They can only handle fluids with low viscosity, solids, or abrasives, such as water, oil, or gas. An example of a pump that uses a closed impeller is a boiler feed pump, which can pump high-pressure and high-temperature water.
Features of Pump Impellers
Another factor that affects the performance and efficiency of a pump is the feature of the impeller. The feature of the impeller refers to the shape, angle, number, and size of the blades, which determine the flow pattern, pressure, and power consumption of the fluid. There are three common features of pump impellers: radial flow, axial flow, and mixed flow.
Radial flow impeller
Radial flow impellers have blades that are perpendicular to the impeller axis. They create high pressure and low flow rates. They are suitable for high-head and low-flow applications, such as water supply, irrigation, or fire fighting. Some of the advantages of radial flow impellers are:
- Handles high pressure fluids without cavitation.
- Provides stable, uniform flow over the impeller.
- Can be designed with various types of blades such as back-curved, forward-curved or straight.
- Available in single or multi-stage pumps.
An example of a pump that uses a radial flow impeller is a turbine pump, which can pump water from deep wells or underground sources.
Axial flow impeller
Axial flow impellers have blades that are parallel to the impeller axis. They create low pressure and high flow rate. They are suitable for low-head and high-flow applications, such as cooling, ventilation, or drainage. Some of the advantages of axial flow impellers are:
- Can handle large volumes of fluids with low power consumption
- Provides smooth laminar flow along the impeller
- Can be designed with various types of blades such as fixed, adjustable or variable pitch
- For single or multi-stage pumps
An example of a pump that uses an axial flow impeller is a propeller pump, which can pump water from a lake, river, or canal.
Mixed flow impellers
Mixed flow impellers have blades that are inclined to the impeller axis. They create a combination of pressure and flow rate. They are suitable for medium-head and medium-flow applications, such as circulation, heating, or air conditioning. Some of the advantages of mixed flow impellers are:
- Handles a wide range of fluids of varying viscosities and densities.
- Provides turbulent and dynamic flow through the impeller.
- Various types of blades can be designed such as radial, axial, or diagonal.
- Available in single or multi-stage pumps.
An example of a pump that uses a mixed-flow impeller is a centrifugal fan, which can pump air or gas for ventilation or combustion.
Applications of Pump Impellers
Pump impellers are widely used in various industries and sectors, such as water supply, irrigation, cooling, heating, circulation, drainage, etc. Pump impellers can meet the specific requirements and challenges of each application, such as pressure, flow rate, viscosity, density, temperature, solids content, corrosion, abrasion, etc.
Some of the examples of pumps that use impellers for different applications are:
Water supply pumps
- Water supply pumps are used to pump water from wells, reservoirs, lakes, rivers, or oceans to the distribution system or the end users.
Water supply pumps require high pressure and flow rate, low viscosity and density, and moderate temperature and solids content.
Water supply pumps often use closed impellers with radial or mixed flow, such as turbine pumps, centrifugal pumps, or jet pumps.
Irrigation pumps
- Irrigation pumps are used to pump water from sources to the fields or crops.
Irrigation pumps require moderate pressure and flow rate, low viscosity and density, and high temperature and solids content.
Irrigation pumps often use open or semi-open impellers with radial or mixed flow, such as trash pumps, propeller pumps, or submersible pumps.
Cooling pumps
- Cooling pumps are used to pump water or other coolants to the heat exchangers or the cooling towers.
Cooling pumps require low pressure and high flow rate, low viscosity and density, and low temperature and solids content.
Cooling pumps often use axial flow impellers with fixed or adjustable blades, such as propeller pumps, axial flow pumps, or fan pumps.
Heating pumps
- Heating pumps are used to pump water or other fluids to the boilers, radiators, or heating systems.
Heating pumps require high pressure and low flow rate, high viscosity and density, and high temperature and solids content.
Heating pumps often use closed impellers with radial or mixed flow, such as boiler feed pumps, multistage pumps, or positive displacement pumps.
Circulation pumps
- Circulation pumps are used to pump water or other fluids in a closed loop or a recirculation system.
Circulation pumps require low pressure and moderate flow rate, low viscosity and density, and moderate temperature and solids content.
Circulation pumps often use semi-open or closed impellers with mixed flow, such as centrifugal pumps, circulator pumps, or inline pumps.
Drainage pumps
- Drainage pumps are used to pump water or other fluids from low-lying areas, basements, or sewers.
Drainage pumps require low pressure and high flow rate, high viscosity and density, and low temperature and solids content.
Drainage pumps often use open or semi-open impellers with axial or mixed flow, such as sump pumps, sewage pumps, or dewatering pumps.
Conclusion
Pump impellers can increase the pressure and flow rate of the fluid, improve the efficiency and performance of the pump, and reduce energy consumption and operating costs. They can also handle various types of fluids, such as water, oil, gas, slurry, etc., and adapt to different operating conditions, such as temperature, viscosity, solids content, etc.
