Pumps operating under negative pressure will leak into the pump from less-developed areas (junction or shaft seal) as the pressure at the inlet and pump inlet will be lower than ambient atmospheric pressure. After the air leaks into the pump, the performance of the pump has a great impact. If the pump is running at the design flow, although some of the air leaks, the air flow has little effect on the performance of the pump due to the large flow rate of the pump, that is, the volume of air Va leaked in and the volume of water Vw is small Keep being taken away by water. The flow rate decreases, the proportion of air gradually increased. As the proportion of air only a few hundredth of water, by centrifugal force centrifugal force is very small, will lead to reduced pump head, flow reduction. The greater the volume ratio of air volume Va to water, the more serious this effect is. Therefore, there is a leaky pump, do not operate in the operation of small or close the exit door approach to adjust the amount of water. Once the water pump, even if the exit door can not be opened to resume water supply, because then the pump is full of air. You must stop the pump and refill it. For a serious leak of water pump, water is also difficult to play after the water, because the pump starts to the fixed speed process, a large number of air leakage, which will lead to falling water, it must eliminate air leaks.