A multistage pump refers to a pump with two or more impellers, which can absorb and pressurize water in multiple stages in sections, so as to lift the water to a very high position. The lift can be increased or decreased according to the needs of the pump impeller stage; when the lift of a single-stage pump requires a two-stage motor, a four-stage motor can be used by increasing the number of impellers, thereby increasing the pump life and reducing the noise of the unit

1. There are many elbows on the water inlet pipe of a vertical multistage centrifugal pump

If there are many elbows on the water inlet pipe, some water flow resistance will be added. And the elbows should be turned in a straight direction, and are not allowed to turn in a horizontal direction to avoid air collection.

2. When installing the water inlet pipe, the horizontal section is horizontal or tilted upward

Doing so will cause air to collect in the water inlet pipe, reduce the vacuum of the water pipe and the water pump, reduce the water suction lift of the water pump, and reduce the water output. The correct approach is: its horizontal section should be slightly tilted toward the water source, not horizontal, and must not be tilted upward.

3. The water inlet of a multistage centrifugal pump is directly connected to the elbow

This will cause uneven distribution of water when it passes through the elbow and enters the impeller. When the diameter of the water inlet pipe is larger than the water pump inlet, an eccentric reducer should be installed. The flat part of the eccentric reducer should be installed on the top, and the inclined part should be installed on the bottom. Otherwise, air will be collected, the water output will be reduced or water will not be pumped, and there will be a knocking sound, etc. If the diameter of the water inlet pipe is the same as that of the water pump inlet, a straight pipe should be added between the water pump inlet and the elbow, and the length of the straight pipe should not be less than 2 to 3 times the diameter of the water pipe.

4. The outlet of the multi-stage centrifugal pump is above the normal water level of the outlet pool

If the outlet is above the normal water level of the outlet pool, although the pump head is increased, the flow rate is reduced. If the outlet must be higher than the water level of the outlet pool due to terrain conditions, an elbow and a short pipe should be installed at the outlet to make the water pipe siphon-type and reduce the height of the outlet.

5. The inlet position of the inlet pipe is incorrect

① The distance between the inlet of the inlet pipe and the bottom and wall of the inlet pool is less than the diameter of the inlet. If there is mud and sand at the bottom of the pool, the distance between the inlet and the bottom of the pool is less than 1.5 times the diameter, which will cause poor water inflow or suck in mud and sand during pumping, blocking the inlet.

② When the water inlet of the inlet pipe is not deep enough, it will cause a vortex on the water surface around the inlet pipe, affecting the water inflow and reducing the water output. The correct installation method is: the water depth of small and medium-sized water pumps shall not be less than 300-600mm, and that of large water pumps shall not be less than 600-1000mm.

6. When installing a bottom valve, the last section of the water inlet pipe is not straight

If installed in this way, the valve cannot close by itself, resulting in water leakage. The correct installation method is: the water inlet pipe with a bottom valve is straight. If it cannot be installed vertically due to terrain conditions, the angle between the water pipe axis and the horizontal plane should be above 60°.