Self-priming pump works: in the pump casing filled with water before starting the pump (or pump housing there own water). After starting the impeller rotation speed of the impeller flow channel in the volute, then the entrance to form a vacuum, so that the water backstop door open, the intake air tube into the pump and reaches the outer edge of the impeller channel through. Self-priming pump is self-priming centrifugal pump, it has a compact structure, convenient operation, stable operation, easy maintenance, high efficiency, long life, and a strong self-priming capacity. Pipeline without having to install bottom valve, pump before work just to ensure that there is quantitative in vivo priming can. Different liquids of different materials can be self-priming.