What is Pump Impellers
An impeller is a rotating iron or steel disc with vanes in a centrifugal pump. Impellers transfer energy from the motor that drives the pump to the fluid being pumped by accelerating the fluid radially outwards from the centre of rotation.
The velocity achieved by the water pump impeller transfers into pressure when the outward movement of the fluid is confined by the pump casing. Impellers are available as vortex or channel impellers.
The dimension of the free passage usually refers to the largest spherical object that may pass through the impeller.
For small and medium-sized sewage pumps, a free passage of 80 mm is normally sufficient. Free passage for large pumps (above 100 l/s) should normally be at least 100 mm. The bigger the free passage, the lower the risk of clogging.
Pansto impeller slurry pumps are built using a range of technologies, for example with large free passage through the water pump impeller, where this is required.
Types of Pump Impellers & Pumps Performance
Pump impellers are vital for transferring motor energy into the fluid being pumped. There are three main types of pump impellers: closed, semi-open, and open. While each design brings unique benefits, selecting the right impeller depends on factors like the fluid being pumped, NPSHa (Net Positive Suction Head Available), and required head pressure. The impeller design also affects the pump curve and the Best Efficiency Point (BEP) of the pump. With this in mind, let’s dive into the three different centrifugal pump impeller types.
1. Closed Pump Impellers
Closed pump impellers feature vanes fully enclosed by back plates. This design prevents fluid from bypassing the vanes thus leading to higher efficiency and pressure output. These impellers are ideal for applications involving high-viscosity liquids, such as oils, or when high pressure is required. They work particularly well for water boosting applications in water and wastewater treatment facilities.
- Pros: Higher efficiency, better pressure output.
- Best for: High-viscosity liquids, pressure-sensitive applications.
2. Semi-Open Pump Impellers
Semi-open pump impellers have partially enclosed vanes, balancing the performance of open and closed impellers. This type offers flexibility, making it a suitable option for applications that require the benefits of both designs. If your fluid has too many free particles for a close impeller, then switch to a semi-open impeller. If you need more pressure or feet of head with an open impeller, switch to a semi-open impeller.
- Pros: Balance between open and closed designs, good for flexible applications.
- Best for: Versatile applications with moderate pressure and fluid types.
Semi Open Pump Impellers
Rubber Pump Impellers
3. Open Pump Impellers
Open impellers allow for large amounts of suspended solids to pass through because the vanes are not attached to a plate. This allows for free flowing particles to easily pass through the volute and leave via the outlet. Open pump impellers excel at pumping slurries and solids laden liquids, but it comes at a cost to efficiency and durability.
- Pros: Able to pump a high amount of solids and heavy slurries.
- Best for: Paper stock pumps and mining applications with heavy slurry.
How to Choose the Right Pump Impeller
Choosing the right impeller design can ensures optimal pump performance. Consider factors like fluid type, system pressure, and NPSHa when making your selection. For expert advice, consult with pump specialists who can assess your system’s needs and recommend the best impeller for your application.
The impact of impeller diameter
As well as the type of impeller, it is important to consider the impeller diameter when specifying a centrifugal pump as this can affect its performance. As you can see, the graph below shows multiple pump curves that represent different impeller sizes and the impact that these have on the flow and head of the pump model in question.
The larger the impeller, the higher the circumferential speed at the impeller output and therefore the greater the head and flow produced by the pump, and vice versa. With this being the case, impellers can be trimmed to meet the specific duty point required by the application at hand. Most centrifugal pumps’ performance curves display the range of impeller trim sizes at which the pump can operate sufficiently. This is then used to determine the impeller diameter needed to achieve the performance requirements.
Impeller trimming is a lot cheaper than using a variable frequency drive to achieve the required duty point. However, the more an impeller is trimmed, the larger the clearance between it and the casing which results in efficiency losses. This is why there is a limit to which a pump’s impeller should be trimmed.
If you have any question about Choosing Pump Impeller,Please Contect us anytime.
Conclusion
Understanding the different types of pump impellers — closed, semi-open, and open — and their unique applications can help you choose the right design for your pump system. Each impeller design offers distinct advantages, and understanding how they affect performance is key to achieving the desired outcomes in your system.