Ordinary centrifugal pump, if the suction liquid level is under the impeller, it should be filled with water in advance when starting, which is very inconvenient. In order to store water in the pump, the inlet of the suction pipe needs to be equipped with a bottom valve. When the pump works, the bottom valve causes a great hydraulic loss. The so-called self-priming pump does not need to be filled with water before start-up (after installation, the first start-up still needs to be filled), after a short period of operation, relying on the function of the pump itself, that is, water can be sucked up and put into normal operation.

Self priming pumps are divided into the following categories according to the principle of action:

1. Gas liquid mixing type (including internal mixing type and external mixing type);

2. Water ring wheel type;

3. Jet type (including liquid jet and gas jet).

Working process of gas-liquid mixed self-priming pump: Due to the special structure of the self-priming pump body, after the pump stops running, there is a certain amount of water in the pump body. After the pump is started again, due to the rotation of the impeller, the air and water in the suction pipeline are fully mixed and discharged to the gas water separation chamber. The gas in the upper part of the gas-water separation chamber overflows, and the water in the lower part returns to the impeller and mixes with the remaining air in the suction pipe again until the pump and the suction pipe are mixed All the gas is discharged, self-priming is completed, and the water is pumped normally. The water ring wheel type self-priming pump is to combine the water ring wheel and the pump impeller in a shell, with the help of the water ring wheel, the gas is discharged to realize self-priming. When the pump works normally, the passage of water ring wheel and pump impeller can be cut off by valve, and the liquid in water ring wheel can be drained. Jet type self-priming pump is composed of centrifugal pump and jet pump (or ejector). Depending on the jet device, vacuum is created at the nozzle to realize suction.