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    The secret of the OEM non-negative pressure unit about the internal mixing impeller inlet of the self-priming sewage pump. The internal mixing refers to the practice of gas-liquid mixing near the impeller inlet. Before the pump is started, the pump body is filled with an appropriate amount of liquid (to swallow the impeller), the return valve is opened, and the press-in chamber is connected to the suction chamber. After the impeller rotates, the liquid in the suction chamber and the impeller is transferred to the press-out chamber through the impeller. Negative pressure is formed at the inlet of the impeller, and the pressure in the suction pipeline is higher than the pressure in the suction chamber, so the suction valve is opened, and the gas in the suction pipeline enters the impeller by suction, and the liquid in the pressure outlet chamber is sucked through the return valve hole. The chamber is sucked to the inlet of the impeller to perform gas-liquid mixing. The impeller and the gas-liquid mixture are sent to the press into the chamber. The OEM non-negative pressure unit has a large enough volume of the gas-liquid separation chamber to reduce the flow rate. It depends on the specific gravity of the liquid and the gas. The gas is separated from the liquid due to the difference between the gas and the liquid. The gas is discharged through the pressure outlet pipe, and the liquid is sucked into the impeller through the return valve hole and mixed with the gas, and then circulates in turn until the gas in the suction pipe is drained. The negative pressure unit knows that at this time the pump has completed the self-priming process and reached normal operation.