There are many different types of impellers including: closed impellers, half open impellers, entirely open impellers, recessed impellers, peripheral impellers and side entry impellers. Each impeller type has its own specific characteristics.
 

A distinction is also made between standard-priming and self-priming centrifugal pumps. In both cases the impeller must always be below the water level, however, self-priming centrifugal pumps are better for air processing and are often constructed so that liquid remains in the pump house so the pumps can be stationed above the level of the liquid.
 

A critical point for centrifugal pumps is always their mechanical seal. These are made in various versions. For chemically aggressive liquids a magnet driven pump is often selected which are hermetically sealed from the atmospere.