There are many factors to consider when selecting an axial split case pump and impeller correctly. 

First, we need to know where the fluid needs to be transported and at what flow rate. The combination of head and flow required is called the duty point. The duty point is directly related to the impeller geometry required. Applications with long vertical pumping (high head) require larger outer diameter impellers than applications with short vertical pumping (pumping).

Another consideration that is directly related to impeller size is the expected solids content in the application. Many applications have a variety of solids in the pumped media. These solids can range from small abrasive debris such as sand or metal shavings to fine fibrous materials to large solids the size of a baseball or larger. The pump and impeller selected must be able to pass these solids while avoiding clogging and damage from wear. Additional consideration must also be given to the equipment downstream of the axial split case pump. While a pump can be selected to pass a specific type of solids, it cannot be assumed that the downstream piping, valves, and other process equipment will have the same solids handling capabilities. Knowing the expected solids content in the liquid is critical not only to selecting the right size pump and impeller, but also to selecting the impeller style that best suits the application.

One of the most common solids handling impellers is the open impeller. This impeller is commonly used in sewage and wastewater treatment and has a geometry that includes passages between the blades with the open side facing the inlet. The spaces between the blades provide a smooth path for the impeller to push incoming solids from the impeller suction hole to the volute and ultimately through the pump discharge.

Another option for handling solids is the vortex or recessed impeller. This type of impeller is mounted within a casing (creating a large open space between the impeller and the suction port) and induces fluid motion through vortices created by the rapid rotation of the impeller. While this approach is not as efficient, it does provide many benefits for solids passage. The main advantages are large free space and minimal obstruction to solids passage.

Pumps used at high altitudes have their own set of solids handling considerations. Since these applications typically use smaller piping, the solids passage size of the entire system must be considered, not just the pump. Typically, the axial split case pump manufacturers offering high-pressure pumps will include a strainer at the inlet to prevent large solids from entering the pump. 

This is ideal for high-pressure applications where minimal solids are expected, but can cause clogging if enough solids accumulate around the screen surface.

There are many factors to consider when choosing the right axial split case pump and impeller, and understanding the various styles of pumps and impellers is often one of the most critical steps.