The key element of a centrifugal pump is the impeller. This rotating component is mounted on the pump shaft and operates inside the pump casing. Equipped with blades, the impeller transfers energy to the liquid and determines how the pump performs in daily operation.

The impeller design has a direct impact on pump performance and on the types of fluids that can be handled. Parameters such as blade shape, number of vanes, impeller diameter and rotational speed strongly influence the pump head, capacity and overall efficiency of the centrifugal pump.

Because no application is the same, there are many different impeller designs available. In the overview of centrifugal impeller pump types, you will find detailed information about the specific characteristics of the most commonly used BBA Pumps impeller models. The main focus is always on finding the right balance between:

• Free passage for solids.
• Hydraulic efficiency.
• Maximum achievable head.
• Resistance to wear.
• Stable performance when pumping air.

This balance is essential for reliable operation in demanding field conditions.

Common impeller types used by BBA Pumps

Enclosed impeller

With an enclosed impeller, the liquid enters through the eye and is guided radially outward. This design delivers high efficiency and high head with a low NPSH requirement. Enclosed impellers are best suited for pumping clear water or lightly contaminated liquids and are commonly used in high‑head applications and mine dewatering.

Semi‑open impeller

A semi‑open impeller has a closed back and open vanes at the front, running with a small clearance against a wear plate. The spacing between the vanes determines the maximum free passage. This makes the semi‑open impeller a versatile choice for dirty water and wastewater. It is often used in all‑round rental pumps where flexibility and reliable solids handling are required. 

Channel impeller

The channel impeller features a single wide channel that creates a large free passage for solids. A wear ring at the suction opening helps maintain efficiency, although this design is less suitable for highly abrasive liquids. Channel impellers are typically used for sewage and wastewater applications, such as sewer bypassing and temporary pumping at wastewater treatment plants

Screw impeller

The screw impeller is a specially designed closed impeller with a corkscrew shape. It is engineered to handle untreated sewage and long‑fibrous materials without clogging. Even at higher speeds or when pumping air‑laden liquids, the pump runs smoothly and vibration‑free. For demanding sewer bypass jobs, the screw impeller is often the preferred solution.

Interesting facts about impellers:

• Just like car tires, pump impellers must be carefully balanced to reduce vibration and extend pump life.
• Casting quality and material selection play a key role in performance. A smooth impeller surface improves hydraulic efficiency.
• In most cases, larger centrifugal pumps with larger impellers operate more efficiently than smaller pumps.
• Well‑designed impellers are fitted with back vanes. These reduce pressure on the mechanical seal and limit axial forces on the bearings.
• Impellers with a large inlet opening and relatively small outer diameter deliver high flow rates at lower head.
• Impellers with a large outer diameter and smaller inlet opening generate higher head at lower flow rates.
• Pump impellers can be trimmed/machined. For example, in cases where the diameter of the impeller has to be reduced due to the available engine power. If the speed of the centrifugal pump remains the same, the head and efficiency of the pump decreases as the impeller diameter is reduced.
• The impeller vanes of centrifugal pumps are designed to rotate in a single direction. If an impeller rotates in the wrong direction, the head and capacity will be much less than if turning in the correct direction.

Is the performance of your centrifugal pump decreasing?

A drop in pump performance is often related to the impeller. Common causes include incorrect rotation direction, blockage by debris or excessive wear. If the clearance between the impeller and the wear plate becomes too large, internal recirculation occurs and efficiency drops.

Air bubbles forming around the impeller or near the inlet opening can also prevent proper pumping, sometimes resulting in no liquid flow at all.

Regular inspection of the impeller and wear components is essential to maintain reliable pump performance and prevent downtime.