The working principle of self-priming pump is: before starting the pump, fill the pump shell with water (or the pump shell itself has water). After starting, the impeller rotates at high speed, so that the water in the impeller channel flows to the volute. At this time, a vacuum is formed at the inlet to open the inlet check valve, and the air in the suction pipe enters the pump and reaches the outer edge through the impeller channel. Self-priming pump is a kind of self-priming centrifugal pump, which has the advantages of compact structure, convenient operation, stable operation, easy maintenance, high efficiency, long service life and strong self-priming ability. There is no need to install a bottom valve in the pipeline, just ensure that there is a fixed amount of liquid in the pump body to work. Self-priming pumps of different materials can be used for different liquids.

There are many types of self-priming pumps, among which molten salt pumps, vacuum pumps, submerged pumps, metering pumps, gear pumps, corrosion-resistant pumps, acid-resistant pumps and fire-fighting pumps flow in the direction of rotation. Then it meets the water flowing from the right backwater hole and flows along the volute. Because the liquid continuously impacts the cascade in the volute, it is continuously crushed by the impeller, and it is strongly stirred and mixed with air to produce a gas-water mixture. Due to the continuous flow, gas and water cannot be separated. The mixture is stripped by the tongue at the outlet of the volute and enters the separation chamber along the short tube. The air in the separation chamber is separated and discharged from the water outlet pipe, while the water still flows to the outer edge of the impeller through the left and right reflux holes and is mixed with the air in the suction pipe. In this way, the air in the suction pipeline is gradually discharged, so that water enters the pump to complete the self-suction process. Sewage pump, self-priming pump, diaphragm pump, screw pump and gear oil pump are all the same, but the difference is that the backwater does not flow to the outer edge of the impeller, but to the inlet of the impeller. When the internal mixing self-priming pump is started, the reflux valve at the lower front of the impeller must be opened to make the liquid in the pump flow back to the inlet of the impeller. Under the action of high-speed rotation of the impeller, water is mixed with air from the suction pipe to form a gas-water mixture, which is discharged into the separation chamber. Here, the air is exhausted and the water returns to the inlet of the impeller from the return valve. This is repeated until the air is exhausted and the water is sucked into the internal mixing self-priming pump. The working principle is the same as that of the external mixing self-priming pump.