Before starting the self-suction pump, fill the pump shell with water (or there is water in the pump shell itself). After starting, the impeller rotates at high speed to make the water flow in the impeller channel flow to the volute. At this time, the inlet forms a vacuum, which opens the inlet backstop door, and the air in the suction tube enters the pump, and reaches the outer edge through the impeller channel. Then it joins with the water coming from the right backwater orifice and flows along the volute. Because the liquid continuously impacts the cascade in the volute, it mixes strongly with the air to form a mixture of gas and water, and continuously flows, so that the gas and water can not be separated. The mixture is peeled off by the tongue at the volute outlet and enters the separation chamber along the short tube. The air in the separation chamber is separated and discharged by the outlet pipe, while the water still flows to the outer edge of the impeller through the left and right backwater holes and mixes with the air in the suction pipe. So repeated circulation, gradually exhaust the air in the inhalation pipeline, so that water into the pump, complete the self-priming process.