What are the reasons why a horizontal multistage centrifugal pump cannot pump water?

Many users encounter a thorny problem when using horizontal multistage centrifugal pumps: the motor is running normally, but no water is coming out of the outlet. The pump may have been running stably the day before, so this sudden "shutdown" not only delays production but also easily causes panic. In fact, most such malfunctions have a clear cause and are not random "sudden events"-mastering basic troubleshooting methods can quickly pinpoint the problem.

• First, check for air leaks in the suction pipe or suction port.

Horizontal multistage centrifugal pumps rely on negative pressure within the pump to draw water. If the suction pipe connection is loose, the pipe wall has cracks, or the suction port is not fully submerged in water (depending on the equipment model, the immersion depth should be at least 20 cm), external air will continuously enter the pump body, disrupting the negative pressure balance. For example, some users, for convenience, only allow the suction port to barely touch the water surface. Although it may appear that the pump can draw water, air will continuously mix in, causing the pump to malfunction.

• Second, check if the impeller is faulty or rotating in reverse.

The impeller is the core component of the pump that transports water. Prolonged transport of water containing silt and impurities will cause impeller blade wear, reducing transport efficiency. If impurities become stuck between the impeller and the pump casing, the impeller will seize up and cannot rotate. An easily overlooked problem is the motor rotation direction: if the wiring is incorrect after maintenance, the impeller will rotate in the opposite direction, causing the water flow to be reversed-naturally, it will be unable to pump water. In this case, the motor wiring needs to be adjusted according to the rotation direction arrow marked on the pump body.

• Third, check if there is any trapped air inside the pump.

If a large amount of air remains in the pump chamber and suction pipe after the pump is used for the first time or after a long period of inactivity, "air lock" will occur. Because air is more compressible than water, the impeller cannot generate sufficient centrifugal force to create effective negative pressure when rotating. The correct operating method is: before starting the pump, open the vent valve, add water to the pump until clean water flows out of the vent valve, and ensure the pump chamber is full of water before starting the pump.

• Fourth, check if the suction is too high.

Every horizontal multistage centrifugal pump has a rated suction head (usually 3-8 meters, refer to the equipment manual for specific details). If the vertical distance from the pump body center to the water surface exceeds the rated value, the negative pressure generated by the impeller will be insufficient to overcome gravity and pump water. For example, some users install the pump on excessively high platforms to save space. Even if the pipes and impeller are in good condition, insufficient suction head will prevent pumping.

• Finally, do not ignore bottom valve malfunctions.

The bottom valve is installed at the bottom of the suction port to prevent backflow. If the valve core is blocked by aquatic plants or stones, or if the sealing surface is worn and aged, water will not be able to enter the pump body, or it will flow back into the water tank after entering. For example, in agricultural irrigation pumps, the bottom valve is easily blocked by weeds. After the pump starts, water will continuously flow back, and the pump cannot maintain the water level, leading to pumping failure. Regularly cleaning the impurities in the bottom valve can prevent such problems.

When a horizontal multistage centrifugal pump experiences a pumping failure, troubleshooting can be performed in the following order: "First, check for air-related issues (venting, leaks); second, check components (impeller, foot valve); and finally, check the installation (suction lift)." In most cases, the problem can be resolved quickly. If the problem persists after troubleshooting, you can contact the HNYB PUMP technical team. We provide one-on-one equipment maintenance guidance to help you minimize downtime losses and ensure stable equipment operation.