Why do the impellers of sewage pumps have different shapes

ATACH Pump Industry offers various types of sewage pumps, such as self-priming non-clogging sewage pumps for ground use, submersible sewage pumps for internal use in liquids, and semi-submersible sewage and waste pumps.

The impellers of sewage pumps are designed in different shapes mainly to meet the demands of various complex working conditions during sewage transportation, balancing key performance indicators such as efficiency, passability and reliability. 

Impellers of different shapes have their own focuses when treating wastewater containing solid particles and fiber impurities, to meet the requirements of specific application scenarios.

Design considerations for differences in impeller shapes

The composition of sewage is complex and may contain large particles, long fibers, sludge and other impurities. The difference in impeller shape directly determines the pump's characteristics in terms of anti-clogging, wear tolerance, and conveying efficiency. For example:

The trade-off between ‌ efficiency and passability

: The closed impeller has a smooth flow channel and high operating efficiency, but it is prone to being entangled by long fibers. Open or channel impellers have a larger space to pass through and are less prone to clogging, but their efficiency is relatively lower. ‌

 Wear and maintenance requirements ‌ : Particles can erode the impeller clearance, leading to a decrease in efficiency. The shape of the impeller should take into account the convenience of maintenance after wear. For instance, an open impeller is easy to clean, while a closed impeller has good sealing performance but is difficult to maintain. ‌

Cavitation and head characteristics ‌ : The geometry of the impeller inlet affects the cavitation performance, and the outlet parameters affect the head (H) and flow rate (Q). For instance, the channel impeller has good anti-clogging performance but weak cavitation performance, while the closed impeller has high efficiency but the net positive suction head (NPSHR) needs to be noted. ‌

Main types of impellers and applicable scenarios

According to the characteristics of sewage, common impeller shapes can be classified into the following categories:

 blade impellers ‌ (including open, semi-open and closed types) :

 open type/semi-open type ‌ : simple to manufacture, easy to clean clogging, suitable for conveying wastewater containing a small amount of solid particles. However, during long-term operation, the abrasion of particles will increase the gap, reduce efficiency and cause vibration. ‌

 closed type ‌ : High efficiency, smooth operation, low axial thrust, but poor non-clogging performance, not suitable for wastewater containing large particles or long fibers. ‌

 swirl impeller ‌ :

The impeller part is partially withdrawn from the flow channel of the pressurized water chamber, and the particles do not come into direct contact with the blades. It has extremely strong anti-entanglement and passing capabilities, making it suitable for high-concentration fiber wastewater. However, its efficiency is relatively low (about 70% of that of the closed impeller). ‌

 channel type impeller ‌ (single channel, double channel, etc.) :

The bladdless design features a curved flow channel and excellent anti-clogging performance, making it suitable for conveying large solid particles. Its efficiency is close to that of a closed impeller, but its cavitation performance is relatively weak. It is mostly used in pressurized inlet pumps. ‌

 spiral centrifugal impeller ‌ :

The spiral blades push suspended particles, causing little damage to the medium and having strong permeability. They are suitable for wastewater containing large particles, long fibers or high concentration, and possess the characteristics of both positive displacement pumps and centrifugal pumps. ‌

How to choose the shape of the impeller?

When making a selection, the composition of the sewage, particle size, concentration and operational requirements should be comprehensively considered

If the sewage contains a large amount of long fibers or large particles (such as construction slurry), it is preferred to choose ‌ swirl ‌ or ‌ channel ‌ impellers to avoid clogging. ‌

If the sewage is relatively clean and high efficiency is desired (such as municipal water supply), a ‌ closed impeller ‌ is more suitable. ‌

In situations where the medium is sensitive to damage (such as food wastewater), the ‌ spiral centrifugal ‌ impeller can reduce particle damage. ‌

In conclusion, the diversity of impeller shapes is aimed at optimizing the comprehensive performance of pumps under complex working conditions. Users should select the matching type based on the actual characteristics of the medium.