Classification of sewage pumps: submersible sewage pump, pipeline sewage pump, self-priming sewage pump, submerged sewage pump and slurry pump (1) Impeller passage blocked If part of the flow passage of the impeller is blocked, it will affect the work of the impeller and lead to the decrease of outlet pressure. Therefore, the pump needs to be removed for inspection and removal of foreign matters. In order to prevent this problem from happening again, if necessary, a filtering device can be added in front of the pump inlet. (2) Internal leakage When the clearance between the rotating part and the stationary part in the pump exceeds the design range, it will lead to internal leakage, which is reflected in the decrease of the discharge pressure of the pump, such as the clearance between the impeller port ring and the interstage clearance of multi-stage pump. At this time, corresponding disassembly and inspection shall be carried out, and the parts causing excessive clearance shall be repaired or replaced. (3) Cavitation at inlet If the suction pressure of the pump is too low, which is lower than the saturated steam pressure of the pumped medium, cavitation will be formed. At this time, check whether the inlet pipeline system is blocked or whether the opening of the inlet valve is too small, or increase the liquid level of the suction pool. (4) Speed reduction The important factors affecting the pump head are the outer diameter of the impeller and the speed of the pump. When other conditions remain unchanged, the pump head is in positive proportion to the quadratic power of the speed. It can be seen that the speed has a great impact on the head. Sometimes if the speed of the pump is reduced due to some external reason, the pump head will be reduced accordingly. At this time, check the speed of the pump. If the speed is not enough, check the cause and solve it reasonably. (5) The operating point deviates to large flow and low head Generally, centrifugal pumps have a continuous downward performance curve, and the flow increases gradually with the decrease of head. In the process of operation, due to some reason, the back pressure of the pump decreases, and the working point of the pump passively shifts to the point of low head and large flow with the curve of the device, which will reduce the head. In fact, this is caused by external factors such as the change of the device, which has no special relationship with the pump itself. At this time, the problem can be solved by increasing the pump back pressure, such as closing the outlet valve a little.