Some centrifugal pump users believe that reducing the pipe diameter can increase the actual head, but in reality, the actual head of the pump is equal to the total head minus the head loss. Once the pump model is determined, the total head is fixed; the head loss mainly comes from the pipe resistance. A smaller pipe diameter naturally results in greater resistance, thus increasing the head loss. Therefore, reducing the pipe diameter does not increase but rather decreases the actual head of the pump, leading to a decrease in pump efficiency. Similarly, when a small-diameter pump is used to pump water through a large pipe, it does not decrease the actual head of the pump. Instead, it reduces the head loss due to the decreased pipe resistance, thereby slightly increasing the actual head. Some operators also believe that using a small-diameter pump with a large pipe will significantly increase the motor load. They think that with the pipe diameter increased, the water pressure on the pump impeller is greater, thus increasing the motor load. However, the pressure of the liquid is only related to the head, not 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 always the same, regardless of the pipe diameter. The only thing is that when the pipe diameter increases, the water flow resistance decreases, resulting in an increase in flow rate and a corresponding increase in power consumption. But as long as the pump operates within the rated head range, it can work normally regardless of the pipe diameter increase, and it can also reduce pipe losses and improve pump efficiency.