There is also a small impeller in front of the main pump impeller – what is its purpose?

Inducer wheel: The function of the inducer wheel in centrifugal pumps. Horizontal multi-stage centrifugal pumps use the head generated by the inducer wheel to increase the pressure for the subsequent centrifugal impellers. The inducer wheel requires only a very low suction head, but this improves the overall suction performance of the pump. In centrifugal impellers, when bubbles develop to a certain extent, they affect the external characteristics and lead to a decline in performance. This is because within the flow channels of the centrifugal wheel, the liquid flows from axial to radial directions (mainly radially). Since the density of liquid is greater than that of gas, under the effect of centrifugal force, bubbles in the liquid stream can easily separate and expand rapidly, thereby blocking the flow channels and causing a sharp deterioration in the pump’s suction capacity. In a centrifugal pump, the flow channels between the impeller blades are relatively long and axial in nature; the relative flow velocity is highest at the outer edge of the impeller. As a result, cavitation occurs first at the outer edge of the impeller. The liquid near the center of the impeller, under the effect of centrifugal force, compresses the cavities at the outer edge, forcing them to move axially along that edge. Once they reach the high-pressure area, these cavities collapse, thereby **limiting the development of cavitation**. The pump’s operating condition is disrupted only when all the flow channels in the impeller are filled with bubbles (at which point the centrifugal wheel also develops bubbles and the flow is interrupted).

It looks like a meat grinder to me It’s not an ordinary centrifugal pump, right? It must be a centrifugal pump used for processing materials with very high viscosity or high sediment content, right? This type of impeller should be called a composite impeller. This set of impellers consists of auger screws together with impellers, and its principle is similar to that of a meat grinder + centrifugal pump = centrifugal pump; P

Induction wheel – you’ll understand its function by searching on Baidu

An inducer wheel is used to reduce the pump’s net positive suction head; with it in place, the pump’s operating range becomes smaller

We have an inducer wheel in front of the impeller, with two spiral-shaped blades.

Induction wheel to prevent cavitation in the main impeller