【2026 Mechanical Equipment】8 Common Mistakes to Avoid When Using Centrifugal Pumps

This post was last edited by The one on 2026-7-18 at 13:25. 1. Using high-head pumps in low-head applications: Many people think that the lower the head, the less load the motor has to handle; therefore, they choose pumps with a high head value when selecting them. In fact, the power consumption of a centrifugal pump is proportional to the actual flow rate. The lower the head, the greater the flow rate, and consequently the higher the motor load. Therefore, when high-head pumps are used in situations where the required head is too low, the motor is very prone to overload, overheat, and even burn out. To protect the motor, the actual head used is generally not less than 60% of the rated head. If it must be temporarily used in applications with low head, a gate valve should be installed on the outlet pipe, and the valve should be closed partially to reduce flow and limit the motor load. Many people mistakenly believe that closing the valve reduces the load on the motor; in fact, the opposite is true: by closing the outlet valve, the flow rate decreases, and thus the motor’s load is reduced.

2. Using large-diameter pumps with small pipes for water pumping: Some people think that a smaller pipe diameter results in a higher head pressure. In fact: Actual head = Total head - Pipe loss head. Once the pump is selected, the total head remains fixed. The smaller the pipe diameter, the greater the pipeline resistance and the higher the head loss; as a result, the actual head decreases and the efficiency drops. Some people also believe that using a small pump with large pipes will significantly increase the load on the motor. In fact, liquid pressure is only related to the head, not to the diameter of the pipes. As long as the head remains constant, the pressure acting on the impeller remains essentially unchanged. An increase in pipe diameter only reduces resistance and leads to a slight increase in flow rate; as long as it remains within the specified range, the pump can operate properly, while losses are reduced and efficiency is improved.

3. The horizontal section of the suction pipe should be installed horizontally or slightly tilted upward. If the horizontal section of the suction pipe is installed horizontally or even tilted upward, air can easily accumulate inside the pipe, which reduces the vacuum level and prevents the pump from drawing in water, resulting in a decrease in the water flow rate. Correct approach: The horizontal section of the suction pipe should be slightly inclined in the direction of the water source; it must not be horizontal, nor should it tilt upward.

4. Too many elbows are used in the water intake pipeline; an excessive number of elbows significantly increases water flow resistance. Moreover, the elbow should turn as much as possible in a vertical direction, rather than horizontally, to avoid air accumulation.

5. The suction pipe elbow is connected directly to the pump inlet; connecting the elbow directly to the pump inlet results in uneven water flow reaching the impeller. If the pipe diameter is larger than that at the pump inlet, an eccentric reducer should be installed with its flat side facing upward and its inclined side facing downward; otherwise, air accumulation is likely to occur, leading to a decrease in water flow, an inability to draw water, as well as vibrations and noise. If the pipe diameter is the same as that of the pump inlet, a straight section of pipe should be added between the elbow and the pump, with a length of not less than 2 to 3 times the pipe diameter.

6. The lowest section of the suction pipe equipped with a bottom valve is not vertical; if this section is not vertical, the bottom valve cannot close properly, resulting in leaks and an inability to draw water properly. Proper installation: The bottom valve section should be installed vertically ； When subject to constraints, the angle between the water pipe and the horizontal plane should be greater than 60°.

7 Incorrect installation location of the suction pipe inlet: ① The suction inlet is too close to the bottom or walls of the tank (within the pipe diameter), which makes it easy for sediment and debris to be drawn in, leading to blockages. General requirement: The distance from the water inlet to the bottom of the tank should be no less than 1.5 times the diameter of the pipe.

② If the submersion depth of the intake is insufficient, vortices form on the water surface, drawing in air and resulting in a decrease in the water output. Proper installation: For small and medium-sized pumps, the submersion depth should be ≥ 300–600 mm. Large pumps: Submersion depth ≥ 600–1000 mm.

8. The outlet should be above the water level in the discharge tank; if it is at a higher level than the normal water level, it will increase the head pressure and reduce the flow rate. If terrain constraints require it to be above the water level, an elbow and a short pipe can be installed at the outlet to create a siphon effect, allowing the outlet to be below the water level.

The following \"Differences between centrifugal pumps and axial flow pumps\" is provided for reference. 1. Working principle - Centrifugal pump: It relies on the rotation of the impeller to generate centrifugal force in order to move the fluid. After entering the pump, the fluid is accelerated by the impeller and ejected in a tangential direction, thereby increasing its kinetic energy; it is then slowed down through the diffuser, where its kinetic energy is converted into pressure energy. - Axial flow pump: The fluid flows in an axial direction; the impeller is usually spiral-shaped, and the fluid is propelled as it passes through the impeller, thereby enabling the transport of the fluid. Axial flow pumps have high flow rates, with relatively small pressure increases.