1. Due to the scouring of the water flow, the inner wall of the pump channel and the water surface of the impeller become rough and uneven, the friction coefficient of the pump inner channel increases, and the water flow rate in the pump is large, so the head loss increases. The hydraulic efficiency is reduced.

2. Due to the reason of adding drugs or water quality in front of the pump, there is serious scaling or corrosion in the pump casing. Serious scaling in the pump casing can increase the wall thickness of the pump casing by about 2 2ram, and scale tumors form on the inner wall of the pump, reducing the volume of the pump, reducing the pumping capacity, and making the flow channel rough, increasing the head loss. Both passenger product efficiency and hydraulic efficiency are reduced.

3. Cavities or cracks are generated in the pump flow passage due to casting defects, cavitation, abrasion, corrosion and chemical erosion caused by the pump processing technology, and vortex is generated when water flows, resulting in energy loss. The hydraulic efficiency is reduced.

4. Cavitation on impeller surface. Due to the negative pressure generated during the operation of the back surface of the blade, when the pressure Pk<Pva, cavitation and honeycomb surface will occur, which will cause cavitation of the pump blade under the effect of electrochemical corrosion.

5. Volume loss and mechanical loss. As the pump has been used for a long time, the leakage and resistance caused by mechanical wear increase, reducing the volumetric efficiency and mechanical efficiency. For the above reasons, the performance of the water pump becomes worse. The operating efficiency is reduced by 2~5%, and the pump efficiency can be reduced by more than 10% in serious cases.