The "self-priming" pump is in fact a standard centrifugal pump, but with a modified pump housing. Because the pump housing has been modified, the suction connection is located above the top of the impeller. This means that liquid always remains in the pump housing after the first filling. As a result, the impeller always has liquid and will therefore create a negative pressure (suction pressure) when starting up that is sufficient to suck in a liquid for a number of meters of water column.
These pumps are mainly used instead of a “normal” pump if there is no so-called free flow of liquid. The pump could, for example, be placed a number of meters above a tank. Self-priming pumps are also similar in structure to "standard" centrifugal pumps, depending on the pressure/capacity:
As standard, the impeller has a suction side in the center that, as suggested, sucks the liquid in through the suction connection in the housing. This is generated because, due to the shape of the impeller blades, the liquid at the outlet (pressure side) is pushed out of the pump housing by a combination of speed and centrifugal force.
The pump can be divided into three parts:
