Mixed flow pumps represent a crucial category of hydraulic machinery that combines the features of both centrifugal and axial flow pumps. These versatile pumping solutions are designed to handle moderate to high flow rates with medium head applications, making them ideal for water supply systems, flood control, irrigation projects, and various industrial processes. 

Rotating Components

The rotating assembly represents the heart of any mixed flow pump, responsible for imparting energy to the fluid being transported. Unlike purely radial or axial flow designs, the mixed flow impeller creates a flow path that moves both radially and axially, hence the name "mixed flow."

The impeller is the most critical rotating component in a mixed flow pump. It features uniquely shaped vanes designed to create the ideal flow pattern that balances radial and axial movement. These impellers typically have fewer vanes than centrifugal pumps, with a design that allows fluid to enter axially and discharge at an angle between axial and radial. The specific geometry of the impeller vanes – including their number, profile, thickness, and angle – significantly affects the pump's performance characteristics.

Connected to the impeller is the pump shaft, which transmits rotational energy from the motor to the impeller. In mixed flow pumps, these shafts are carefully engineered to withstand both torsional loads and the axial and radial hydraulic forces produced during operation. Shaft sleeves are often utilized to protect the shaft from erosion, corrosion, and wear, particularly in areas where the shaft passes through sealing arrangements.

Another crucial rotating component is the shaft coupling, which connects the pump shaft to the motor shaft. These couplings must accommodate minor misalignments while efficiently transferring torque. Depending on the application, mixed pumps may use flexible couplings, rigid couplings, or specialized designs tailored to specific operational requirements.

Some advanced mixed flow pump designs include rotating wear rings attached to the impeller. These wear rings work in conjunction with stationary wear rings to maintain proper clearances and control leakage between high-pressure and low-pressure areas, enhancing overall efficiency without requiring extensive maintenance.

Stationary Components

While rotating components generate the hydraulic energy, the stationary components of a mixed flow pump guide the flow, provide structural support, and create the pressure containment necessary for effective operation.

The pump casing, also called the volute or bowl in some designs, is the main pressure-containing component that houses the impeller and directs flow from the impeller outlet. In mixed flow pumps, the casing design is particularly important as it must efficiently convert velocity energy from the impeller into pressure energy while minimizing hydraulic losses. The distinctive shape of mixed flow pump casings reflects their unique flow pattern, with a geometry that gradually expands to reduce the velocity and increase the pressure of the fluid.

Suction and discharge nozzles form critical parts of the stationary assembly. The suction nozzle is engineered to deliver fluid to the impeller eye with minimal turbulence, often featuring a bell-shaped entrance to reduce entrance losses. The discharge nozzle, meanwhile, must efficiently conduct the high-pressure fluid from the casing to the discharge piping system. For larger mixed pump installations, these nozzles may incorporate stiffening ribs or other structural elements to withstand the significant forces involved.

Diffusers are another vital stationary component in many mixed flow pump designs. Positioned immediately after the impeller, diffusers contain fixed vanes that guide the flow and convert kinetic energy into pressure energy more efficiently than a simple volute. The diffuser vanes are carefully designed to match the exit angle of the fluid leaving the impeller, minimizing shock losses and improving overall pump efficiency.

Wear rings represent an essential stationary component that works in conjunction with the rotating assembly. These replaceable components are installed in the casing to create a controlled clearance with the impeller or impeller wear rings. By limiting internal recirculation between the high-pressure and low-pressure regions, wear rings significantly enhance volumetric efficiency. As their name suggests, these components are designed to wear rather than allowing more expensive components to deteriorate, making them relatively easy to replace during routine maintenance.

Sealing systems are crucial stationary components that prevent fluid leakage where the shaft penetrates the casing. Mixed flow pumps may utilize packing, mechanical seals, or labyrinth seals depending on the application requirements. In applications where absolute sealing is critical or where the pumped fluid is hazardous, double mechanical seals with barrier fluid systems may be employed to guarantee containment.

Bearing System

The bearing system provides the foundation for reliable operation of mixed flow pumps by supporting the rotating assembly and managing the various forces generated during operation. Without a properly designed bearing system, even the most precisely engineered pump would quickly fail.

Radial bearings support the shaft and handle the forces perpendicular to the shaft axis. In mixed flow pumps, these forces can be substantial due to hydraulic imbalances and the weight of the rotating components. Common radial bearing types used include rolling element bearings (ball or roller bearings) for smaller units and journal bearings (sleeve bearings) for larger applications. The selection depends on factors such as load capacity, speed, maintenance requirements, and expected service life.

Thrust bearings manage the axial forces generated during pump operation. In mixed pumps, these axial forces can be significant due to the pressure differentials across the impeller and the axial component of the flow. Angular contact ball bearings, spherical roller thrust bearings, or tilting pad thrust bearings are commonly employed depending on the magnitude of the thrust load. In some designs, hydraulic balancing devices are incorporated to reduce the net thrust and minimize the load on thrust bearings.

Bearing housings provide structural support for the bearings while also containing lubrication and often incorporating cooling systems. These housings must be precisely machined to ensure proper bearing alignment and are typically designed for easy access during maintenance. In larger pumps, the bearing housings may include instrumentation connections for monitoring bearing temperatures, vibrations, and other operational parameters.

Lubrication systems are integral to the bearing system, providing the essential medium for reducing friction, removing heat, and preventing wear. Mixed flow pumps may utilize grease lubrication for smaller units or oil lubrication systems for larger applications. Oil lubrication systems may be simple oil bath arrangements or more complex forced-circulation systems with cooling and filtration capabilities for demanding applications.

Understanding the intricate components of mixed flow pumps is essential for selecting the right pump for your specific application, ensuring proper installation, and implementing effective maintenance practices. At Tianjin Kairun Pump Co., Ltd, we specialize in designing and manufacturing high-quality mixed flow pumps with customizable features to meet your unique operational requirements.

Our mixed flow pumps are engineered with precision-crafted rotating components, durable stationary elements, and reliable bearing systems that ensure long-term performance and efficiency. All our products are certified to meet relevant industry standards, guaranteeing quality, safety, and optimal performance even in demanding environments.

Ready to find the perfect mixed flow pump solution for your application? Contact our customer service department today at catherine@kairunpump.com to discuss your requirements and discover how our expertise in pump technology can benefit your operations. Our team of specialists is standing by to provide comprehensive support from selection through installation and beyond with our industry-leading after-sales service.

References

• Karassik, I.J., Messina, J.P., Cooper, P., & Heald, C.C. (2008). Pump Handbook (4th ed.). McGraw-Hill Education.

• Gülich, J.F. (2014). Centrifugal Pumps (3rd ed.). Springer.

• Tuzson, J. (2000). Centrifugal Pump Design. John Wiley & Sons.

• Lobanoff, V.S., & Ross, R.R. (2013). Centrifugal Pumps: Design and Application (2nd ed.). Elsevier.

• American National Standards Institute. (2016). ANSI/HI 1.3-2013 Rotodynamic Pumps for Design and Application.