Feb. 09, 2022

OEM Impeller


Although there are numerous styles/designs offered by pump manufacturers, most slurry pump offerings boil down to a variation of one of two basic designs, with a third design, slightly less common, that is becoming more widely used every year.



The first, and arguably the most, rugged design is the closed impeller. In this design, the liquid follows a path down a tunnel formed on the sides by the vanes and is “closed” in on the top and bottom (or front and back depending on shaft orientation) by two shrouds. The two images below illustrate this design.



The semi-open impeller is very similar in its design to the closed impeller. The one major difference is the absence of the front shroud. The vanes of a semi-open impeller are supported by a back shroud only and the impeller is completely void of a front shroud. In the absence of a front impeller shroud, the front wear plate completes the tunnel used to accelerate the slurry within the pump.



The third and slightly less common slurry impeller is the recessed impeller. Often called “torque flow” impellers, they create a centrifugal force in a unique manner.  Instead of accelerating liquid down the vanes, these impellers use the vanes to create a hydraulic coupling. The coupling then spins the slurry within the casing, thereby creating the centrifugal force required to create discharge pressure.

With the vanes basically out of the normal flow path, erosion is minimized and the vanes do not need to be as thick as they have to with other impeller styles.  In fact, finer blades increase efficiency and are therefore often deemed more desirable.

I hope these short descriptions help clarify the terms “closed”, “open” and “recessed”.  



  • Vane shape

The shape of a vane can affect the direction and magnitude of flow inside the pump as well as overall pump efficiency and wear life.

Radial flow: These are paddle-wheel shaped vanes that convert axial flow into radial flow (i.e., outward from the center) as the impeller turns. These are simple to manufacture but inefficient in slurry applications.

Axial flow: These resemble propeller or turbine vanes. In contrast to radial vanes, these vanes do not change the flow direction. They are highly efficient in some applications but are not optimal in slurry pumps as they can wear quickly.

Mixed flow: These vanes are the most common in slurry pumps; they have a twisted design for optimal effectiveness. They gradually convert flow from axial to radial, and are more efficient than radial vanes and more sturdy than axial vanes.

  • Vane angles

An impeller has an inlet angle (i.e., a leading edge near the center), an outlet angle (i.e., a trailing edge near the pump wall), and a vane overlap.

Inlet angle: This is designed for shock-free fluid entry at the pump’s best efficiency point, which improves pump efficiency, reduces wear, and decreases risk of cavitation.

Outlet angle: Higher outlet angles increase the head at a given speed, at the cost of lower efficiency and wear performance. Lower outlet angles increase efficiency and vane length, at the cost of reduced head and, in some cases, vane clearance. Outlet angles are usually optimized to achieve a balance of these factors.

Vane overlap: Positive overlap is best for wear performance because it minimizes recirculation. “Turn downs” are common in centrifugal pumps, which trim the vane’s outer diameter. This can reduce vane overlap and length, so they should be limited to about 10% of the vane’s diameter.

  • Vane quantity

When it comes to vane quantity, more is not always better. More vanes can increase head at a given speed, improve efficiency, and reduce the risk of damage from vane pass. On the other hand, higher vane quantity can reduce the space between vanes, which can cause clogs when processing larger particles. It also requires a higher inlet pressure to prevent cavitation and reduces possible vane length overall. Most of our slurry pumps use three to five vanes; water pumps often feature six or more.

Three vanes: This design is optimal when low suction pressure and large sphere pressure are preferred. Wear performance is usually a lower priority in this design.

Four vanes: This provides a good balance between most factors, including wear performance, vibration, and passage size.

Five vanes: We opt for this design when wear performance is critical, and passage size requirements and available suction pressure are reasonable.


If you have questions about Slurry Pump Impeller or need a Slurry Pump Impeller sized for your slurry application, contact us!