Centrifugal pumps are classified as self-priming if they have the capability to handle liquids, gases and liquid/gas mixtures.
The pump suction pipe is then air-evacuated without any special external suction devices.
Centrifugal pumps without external or internal suction devices can be operated at a suction lift if the pump body is filled with water before starting the actual fluid displacement. Due to the function of a non-return valve the fluid will be retained within the pump body after switch-off.
The construction required for for self-priming capability has a negative effect on the pump efficiency.
Suction Lift With Non-Selfpriming Centrifugal Pumps