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How to Use Centrifugal Pumps Correctly 1. Using high-head pumps for low-head pumping Many people believe that the lower the pumping head, the less load is placed on the motor. Guided by this mistaken perception, when purchasing water pumps, people often choose a very high head for them. In fact, for centrifugal water pumps, once the pump model is determined, the power consumption is proportional to the actual flow rate of the pump. The flow rate of the water pump decreases as the head increases; therefore, the higher the head, the lower the flow rate, and consequently the lower the power consumption. Conversely, the lower the head, the greater the flow rate, and thus the greater the power consumption. Therefore, to prevent the motor from overloading, it is generally required that the actual pumping head of the water pump not be lower than 60% of the rated head. Therefore, when high head is used for pumping at too low a head, the motor is prone to overload and overheat, and in severe cases the motor can be damaged. In case of emergency use, a gate valve must be installed on the outlet pipe to regulate the water flow (or the small outlet can be blocked with wood or similar materials) in order to reduce the flow rate and prevent the motor from overloading. Pay attention to the motor’s temperature rise; if the motor overheats, reduce the flow rate at the water outlet or shut it down promptly. This can also lead to misunderstandings; some operators believe that blocking the outlet and forcing a reduction in flow rate will increase the load on the motor. In fact, the opposite is true: regular high-power centrifugal pump irrigation units are equipped with gate valves on their outlet pipes. To reduce the electrical load on the motor when the unit starts, the gate valve should be closed first, and then gradually opened after the motor has started – that’s the reason for this. II. Using a large-diameter water pump with small pipes for pumping water Many people believe that this approach can increase the actual head pressure, but in fact, the actual head pressure of a water pump = total head pressure – loss head pressure. Once the pump model is determined, the total head remains constant ； The head loss is primarily caused by pipeline resistance; the smaller the pipe diameter, the greater the resistance, and thus the higher the head loss. As a result, when the pipe diameter is reduced, the actual head output of the pump does not increase – instead it decreases, leading to a reduction in the pump’s efficiency. Similarly, when a pump with a small pipe diameter is used to draw water through large pipes, it does not reduce the actual head of the pump; instead, the resistance in the piping decreases, which reduces the loss of head and thus increases the actual head. Some operators believe that when using large pipes to draw water with pumps of small diameter, it will inevitably **increase the load on the motor. They argue that as the pipe diameter increases, the pressure of the water in the outlet pipe on the pump’s impeller rises, which in turn **increases the load on the motor. What is not known is that the magnitude of liquid pressure depends only on the height of the lift, and not on the cross-sectional area of the pipe. As long as the head remains constant and the impeller size of the pump does not change, the pressure acting on the impeller is constant regardless of the pipe diameter. Simply put, when the pipe diameter increases, the flow resistance decreases, which leads to an increase in flow rate; at the same time, power consumption also increases slightly. As long as it remains within the rated head range, the pump can operate properly regardless of the increase in pipe diameter; moreover, this reduces pipeline losses and improves the pump’s efficiency. III. When installing the water inlet pipeline, ensure that the horizontal section is level or slightly tilted upward. Doing so will cause air to accumulate inside the inlet pipe, reducing the vacuum level in the pipe and the pump, which in turn lowers the pump’s ability to draw water and reduces the flow rate of water. The correct approach is: its horizontal section should be slightly inclined in the direction of the water source; it should not be horizontal, nor should it tilt upward. IV. Many elbows are used in the inlet pipeline. If many elbows are used in the inlet pipeline, it will increase the local water flow resistance. Furthermore, the elbow should turn vertically; turning horizontally is not allowed to prevent air from accumulating. V. The water inlet of the pump is connected directly to the elbow, which results in uneven distribution of the water flow as it passes through the elbow and enters the impeller. When the diameter of the water inlet pipe is larger than that of the pump’s inlet, an eccentric reducer should be installed. The planar part of the eccentric reducer should be installed on top, while the inclined part should be installed at the bottom. Otherwise, air will accumulate, the water output will decrease or no water can be drawn up, and there will be knocking sounds and similar issues. If the diameter of the water inlet pipe is equal to that of the pump’s water inlet, a straight pipe should be added between the pump’s water inlet and the elbow, with the length of this straight pipe being no less than 2 to 3 times the diameter of the pipe. VI. The lowest section of the water inlet pipe equipped with a bottom valve is not vertical. When installed in this way, the valve cannot close on its own, resulting in leaks. The correct installation method is: for the inlet pipe equipped with a bottom valve, the lowest section should preferably be vertical. If vertical installation is not possible due to topographical constraints, the angle between the water pipe axis and the horizontal plane should be at least 60°. VII. The inlet of the water inlet pipe is not in the correct position. (1) The distance between the inlet of the water inlet pipe and the bottom as well as the walls of the water tank is less than the diameter of the inlet. If there is sediment or other debris at the bottom of the pool, and the distance between the water inlet and the bottom of the pool is less than 1.5 times the diameter, it will result in poor water intake during pumping, or sediment and debris being drawn in and blocking the water inlet. (2) When the water entry depth at the inlet of the water inlet pipe is insufficient, it causes vortices to form on the water surface surrounding the pipe, which affects water intake and reduces the flow rate of water output. The correct installation method is: for small and medium-sized water pumps, the water intake depth should not be less than 300–600 mm, while for large water pumps, it should not be less than 600–1000 mm. VIII. The outlet should be above the normal water level of the water discharge tank. If the outlet is above this level, it increases the pump’s head pressure but reduces the flow rate. If, due to topographical constraints, the outlet must be at a higher level than the water level in the outlet tank, elbows and short pipes should be installed at the pipe outlet to create a siphon effect and reduce the height of the outlet.