There are many structural types of self-priming pumps, including molten salt pumps, vacuum pumps, submersible pumps, metering pumps, gear pumps, corrosion-resistant pumps, acid resistant pumps, and fire pumps that flow in the direction of rotation. Then it merges with the water flowing from the right return hole and flows along the snail shell. Due to the continuous impact of the liquid on the blades inside the snail shell, it is constantly shattered by the impeller and strongly mixed with the air, generating a mixture of gas and water that flows continuously and cannot be separated. The mixture is stripped off by the tongue at the outlet of the snail shell and enters the separation chamber along the short tube. The air in the separation chamber is separated and discharged through the outlet pipe, while the water still flows towards the outer edge of the impeller through the left and right return holes and mixes with the air in the suction pipe. Repeat this process repeatedly, gradually exhausting the air in the suction pipeline and allowing water to enter the pump, completing the self-priming process. The sewage pump, self-priming pump, oil pump, diaphragm pump, screw pump, and gear oil pump are the same, the only difference is that the return water does not flow towards the outer edge of the impeller, but towards the inlet of the impeller. When starting the internal mixed self-priming pump, the reflux valve below the impeller must be opened to allow the liquid in the pump to flow back to the impeller inlet. Under the high-speed rotation of the impeller, water mixes with the air from the suction pipe, forming an air-water mixture that is discharged into the separation chamber. Here, the air is expelled while the water returns to the impeller inlet through the reflux valve. Repeat this process with a self-priming pump until all air is expelled, and then suction water into an internal mixing self-priming pump. The working principle is the same as that of an external mixing self-priming pump.
The self-priming height of a self-priming pump is related to factors such as the sealing gap in front of the impeller, the pump speed, and the liquid level in the separation chamber. The smaller the sealing gap in front of the impeller, the greater the self-priming height, generally taken as 0.3~0.5 millimeters; When the gap increases, except for the decrease in self-priming height, the pump's head and efficiency also decrease. The self-priming height of the pump increases with the increase of the circumferential velocity u2 of the impeller, but when it reaches the maximum self-priming height, the number of revolutions increases and the self-priming height no longer increases. At this time, only the self-priming time is shortened; When the rotation speed decreases, the self-priming height decreases accordingly. Under other constant conditions, the self-priming height also increases with the increase of water storage height (but cannot exceed the optimal water storage height of the separation chamber). In order to better mix air and water in a self-priming pump, the number of blades on the impeller should be reduced to increase the pitch of the blade array; It is also advisable to use semi open impellers (or impellers with wider impeller channels), which makes it easier for the return water to penetrate deeply into the impeller cascade.
Most self-priming pumps are paired with internal combustion engines and installed on movable carts, making them suitable for field operations.
Article source: Baidu Baike excerpt