How Do Semi-Open and Enclosed Impellers Differ in Submersible Vertical Turbine Pumps?
As the core hydraulic component of the submersible vertical turbine pump, the impeller plays a decisive role in determining the hydraulic performance, operational stability, and fluid compatibility of the unit. Among the various impeller designs, the semi-open and enclosed (closed) impellers are the two most common types.
This article analyzes their differences in structure, performance, and application suitability to help engineers select the optimal impeller design for specific operating conditions.
I. Structural Differences
The semi-open impeller has a back shroud only, with the blades partially exposed and forming flow channels in conjunction with the pump casing.
In contrast, the enclosed impeller features both front and back shrouds, completely covering the blades to form a sealed fluid passage.
These structural distinctions lead to notable differences in manufacturing precision, clearance adjustment, and maintenance methods:
The semi-open impeller has a simple design, easy to machine, clean, and adjust; it also offers better passage capability, reducing clogging risk.
The enclosed impeller has stronger blade rigidity, lower volumetric loss, and higher hydraulic efficiency.
II. Performance Comparison
1. Hydraulic Efficiency
The enclosed impeller provides a fully enclosed flow passage, minimizing fluid energy losses. Consequently, it typically achieves higher efficiency than the semi-open impeller, especially suitable for high-head and high-efficiency applications.
2. Anti-Clogging Performance
The semi-open impeller, with its exposed blades and wider flow channels, is more tolerant of fluids containing suspended solids or impurities, reducing clogging and wear risks. It is well-suited for handling slightly contaminated or particle-laden water sources.
3. Wear Resistance and Maintenance
The enclosed impeller is more sensitive to abrasive media; fluids containing sand or hard particles may cause channel wear or impeller imbalance. Conversely, the semi-open impeller is easier to inspect and maintain, and performance can often be restored by simply adjusting the clearance.
4. Operational Stability
The enclosed impeller offers excellent dynamic balance, resulting in lower vibration and noise levels. The semi-open impeller, however, may experience slightly reduced stability due to axial thrust and uneven flow distribution.
III. Application Suitability
Semi-Open Impeller
Best suited for pumping river water, lake water, sewage, sandy water, or fluids containing small solid particles. It performs well in complex or impurity-rich environments such as irrigation systems, mine drainage, and raw-water intake stations.
Enclosed Impeller
Ideal for clean water or treated fluids, typically used in municipal supply systems, industrial cooling loops, and energy-efficient pump stations.
Its high efficiency and low energy consumption make it the preferred option for continuous operation and applications demanding consistent hydraulic performance.
IV. Conclusion
When selecting a submersible vertical turbine pump, the choice of impeller type should consider the fluid properties, operating conditions, and efficiency requirements:
For clean fluids and conditions requiring high efficiency and stable performance, the enclosed impeller is the optimal choice.
For contaminated or particle-laden fluids, or in maintenance-challenging environments, the semi-open impeller offers greater practicality and reliability.
Selecting the appropriate impeller structure not only enhances the efficiency and reliability of the pump but also significantly extends equipment life, reduces maintenance costs, and ensures safe and efficient pump operation.
