Typically there are two types of self priming centrifugal pumps:
1) Open impeller self priming pumps e.g. EPA pumps, which are used for pumping liquids with soft solids.
2) Closed impeller self priming pumps e.g. Lowara BG, Ebara JESX, Ebara JEX & Ebara AGA/AGC, which are used to extract clean water from underground tanks and shallow wells.