Working structure and principle of self-priming pumps

The self-priming pump is a type of self-priming centrifugal pump; it features a compact structure, easy operation, stable performance, simple maintenance, high efficiency, long service life, as well as a strong self-priming capability. There is no need to install a foot valve in the pipeline; before operation, it is sufficient to ensure that a certain amount of liquid is stored inside the pump. Different liquids can require self-priming pumps made of different materials. The working principle of a self-priming pump is that the pump chamber is filled with water before the pump is started (or there is already water in the pump chamber). Upon startup, the high-speed rotation of the impeller causes the water in the impeller channels to flow toward the volute; this creates a vacuum at the inlet, which opens the inlet check valve. Air from the suction pipe enters the pump and moves through the impeller channels to the outer edge. A centrifugal pump operates by using the rotation of an impeller to cause water to move in a centrifugal direction. Before starting the water pump, it is necessary to fill the pump casing and the suction pipe with water. Then the motor is started, causing the pump shaft to drive the impeller and the water to rotate at high speed; as a result of centrifugal force, the water is thrown toward the outer edge of the impeller and flows through the channels in the volute-shaped pump casing into the pressure pipeline of the water pump.

For ordinary centrifugal pumps, if the liquid level at the suction side is below the impeller, it is necessary to fill them with water in advance before starting. To pump water into the tank, a foot valve must be installed at the inlet of the suction pipe. When the pump is in operation, the foot valve causes significant hydraulic losses. A self-priming pump does not require priming before being turned on (priming is still necessary the first time it is used after installation); after operating for a short period of time, it can draw water up by its own mechanism and start working normally. Working principle of self-priming pumps: 1. Gas-liquid mixing type (including internal mixing and external mixing): Due to the special structure of self-priming pumps, a certain amount of water remains inside the pump after it stops running. When the pump starts again, the rotation of the impeller causes the air in the suction pipe to mix thoroughly with the water; this mixture is then sent to the gas-water separation chamber. The gas at the top of this chamber escapes, while the water at the bottom returns to the impeller, where it mixes again with any remaining air in the suction pipeline. This process continues until all the gas in the pump and suction pipe has been removed, allowing the pump to start pumping water normally. 2. Water ring type self-priming pump: It combines a water ring wheel with a pump impeller within one casing, and uses the water ring wheel to expel gas, thereby achieving self-priming. Once the pump is operating normally, the passage between the water ring wheel and the pump impeller can be blocked using a valve, and the liquid inside the water ring wheel can be drained. 3. Jet self-priming pump: Composed of a centrifugal pump and a jet pump (or ejector), it relies on a jetting device to create a vacuum at the nozzle in order to achieve suction.

https://bbs.hcbbs.com/forum.php?mod=viewthread&tid=897573 The forum has animation videos showing the working principles of various pumps; you can search for them.

They are both centrifugal pumps; the only difference is that self-priming pumps have a self-priming function. Centrifugal pumps require water to be filled in each time they are started, whereas self-priming pumps only need water to be filled in once, at the time of first use, and no further filling is required thereafter.