Thread Content
Pumps that are in operation for extended periods of time may sometimes experience cavitation; the impeller can be damaged by this phenomenon, which affects the continuity of the fluid flow. This reduces the pump’s power and flow rate, causes loud noises and vibrations, and can further corrode the exterior of the pump. Therefore, it is necessary to improve the pump’s resistance to cavitation. Below are some measures that can be taken to enhance a pump’s resistance to cavitation. 1. Measures to increase the effective net positive suction head of the water pump’s inlet device: (1) Replace the pump’s suction device with a backflow device ； (2) Reduce the installation height of the pump in the water pump suction unit ； (3) Increase the pressure of the liquid level in the liquid storage tank before the pump to raise the effective net positive suction head of the water pump. (4) Reduce the flow losses in the pipeline ahead of the pump; for example, shorten the pipeline as much as possible within the required range, reduce the flow velocity in the pipeline, minimize the use of bends and valves, and maximize the opening degree of the valves. 2. Measures to improve the cavitation resistance of the water pump itself: (1) Improve the structural design from the pump’s inlet to the vicinity of the impeller. Increasing the flow area, enlarging the radius of curvature at the inlet section of the impeller shroud, reducing the rapid acceleration and pressure drop of the fluid flow, appropriately reducing the thickness at the blade inlet and rounding it to make it more streamlined can also reduce the acceleration and pressure drop around the blade tip. Improving the surface finish of the impeller and blade inlets helps to reduce frictional losses. Extending the edge of the blade inlet toward the impeller inlet allows the fluid flow to be subjected to work earlier, thereby increasing pressure. (2) A double-suction impeller is used, allowing the fluid to enter the impeller from both sides; as a result, the inlet cross-section doubles, and the inlet flow velocity can be reduced by half. (3) A pre-induction impeller is used to enable the fluid flow to do work in advance within the pre-induction wheel, thereby increasing the fluid pressure. (4) Materials resistant to cavitation should be used. Practice has shown that the higher the strength, hardness, and toughness of a material, as well as its chemical stability, the better its resistance to cavitation. (5) A slightly larger positive attack angle is adopted in the design conditions to increase the blade inlet angle, reduce bending at the blade inlet, minimize blade blockage, thereby enlarging the inlet area and improving operating conditions under high flow rates to reduce flow losses; however, the positive attack angle should not be too large, as this would affect efficiency. 3. Reducing the required net positive suction head: Increasing the diameter at the inlet of the impeller as well as the width at the inlet of the blades can reduce the critical cavitation margin of the pump. Lowering the inlet velocity and relative velocity of the impeller helps to minimize bubble formation. By using multi-stage pump impellers, induction wheels, and arranging induction wheels in such a way that the pressure wheels operate together after being mounted on the same axis, it is possible to increase the pressure applied to the feed flow of the pump impeller, thereby enhancing the pump’s resistance to cavitation. 4. Improve the cavitation resistance of the components that handle flow. It is necessary to use water pump components made of materials with strong resistance to cavitation, in order to reduce damage to these components and extend the pump’s service life. For example, materials such as manganese, bronze, and stainless steel can be used for casting, and the surfaces can be coated with polymers or treated through laser spraying; this will enhance the pump’s resistance to cavitation. 5. Improve the cavitation resistance of imported equipment. The design of the pump intake equipment and pipeline systems is closely related to the cavitation margin; in order to meet the requirements regarding the dynamic pressure drop of the pump, it is necessary to design effective intake equipment that helps to increase the cavitation margin provided by the pump manufacturer as much as possible. Secondly, to determine the water absorption rate of the pump appropriately, it is necessary to fully consider the various operating conditions that the pump manufacturer may encounter during use; the determined water absorption rate should meet the requirements under all such conditions. In addition, a suitable intake pipeline was selected to minimize the length of the inlet pipe for the horizontal pump as well as unnecessary fittings; the diameter of the inlet pipe was increased appropriately to reduce hydraulic losses at the water inlet and improve the cavitation margin at the pump inlet. It can be seen from this that the three methods to improve a pump’s resistance to cavitation are to reduce the required cavitation margin, to enhance the cavitation resistance of the components through which fluid flows, and to improve the cavitation resistance of the water inlet equipment. Furthermore, during the operation of the pump, depending on the specific conditions of the pumping station, control methods such as variable valves, variable speed, and variable angle can be employed to prevent the pump’s operating conditions from deviating too much from the planned conditions.