Operating Principle of Self-Priming Pumps

The operating principle of an externally mixing self-priming pump is as follows: before startup, the pump casing is filled with water (or retains water from previous operation). Upon startup, the impeller rotates at high speed, driving the water within the impeller channels toward the volute casing. This creates a vacuum at the inlet, causing the inlet check valve to open; air from the suction pipe is drawn into the pump and travels through the impeller channels to the outer periphery. Meanwhile, water discharged by the impeller into the air-water separation chamber flows back to the impeller's outer periphery via left and right return ports. Driven by pressure difference and gravity, the water returning through the left port jets into the impeller channels, where it is broken up by the impeller, mixes with the air from the suction line, and is flung toward the volute casing to flow in the direction of rotation.
The operating principle of an internally mixing self-priming pump is the same as that of the externally mixing type.
Most self-priming pumps are paired with internal combustion engines and mounted on portable carts, making them suitable for field operations.