What is the difference between a self-priming and a centrifugal pump?

Centrifugal pumps do not have seals between the suction and discharge sides of the pump, meaning they are not self-priming and cannot evacuate gases and air if the pump is above the fluid level. In water installations, this means that a self-priming pump does not need to be located below a water tank; instead, it can operate laterally or above the level of the fluids being drawn through the pump.