I. Hazard of cavitation of centrifugal pump
When the liquid sucked in the pump casing is just vaporized due to the pressure reduction at the suction port of the pump, the The inner wall brings a huge hydraulic impact, which makes the shell wall corrode as if it is “gas”, which is called cavitation. Centrifugal pump cavitation will produce vibration and noise, which will affect the working performance of the pump. When the cavitation develops to a certain extent, a large number of bubbles will be generated, which will block the flow channel and significantly reduce the flow rate, head, and efficiency of the pump. There will be damage to the material of the runner: mainly fatigue erosion of the metal near the blade inlet.
2. Causes and solutions of centrifugal pump cavitation
The reasons for centrifugal pump cavitation failure mainly include the following:
1. The liquid level is too low.
2. The resistance of the inlet pipeline is too large or the pipeline is too thin.
3. The sealing packing at the pump inlet is leaking, and the valve and flange connection is not strict.
4. The temperature of the conveyed liquid is too high to generate gas.
5. The inlet of the pump impeller and the filter are blocked.
6. The flow rate is too large, which means that the outlet valve is too open.
7. The installation height is too high, which affects the suction volume of the pump.
8. Selection issues, including pump selection, pump material selection, etc.
Solution:
1. If the liquid level is too low, increase the liquid level.
2. If the inlet sealing packing is missing, adjust the amount of packing leakage. The valve and flange connections are not strict, and the sealing should be tightened or replaced.
3. If the temperature of the conveyed liquid is too high, reduce the temperature of the conveyed liquid.
4. If the pump impeller inlet or filter screen is blocked, clean the impeller inlet and filter screen.
5. If the pump displacement is too small, re-adjust the pump displacement to control the flow within a reasonable range.
Three, how to prevent cavitation failure of centrifugal pump
1. Structural measures
Adopt Double suction impeller to reduce the flow rate through the impeller, thereby reducing the NPSH of the pump. A booster front pump is installed in front of the large high-lift pump to increase the liquid inlet pressure. The impeller is specially designed to improve flow conditions at the inlet of the blades. An inducer is added in front of the centrifugal impeller to increase the flow pressure into the impeller.
2. Installation height of the pump
The higher the installation height of the pump, the lower the inlet pressure of the pump. inlet pressure. Therefore, a reasonable determination of the installation height of the pump can avoid cavitation of the pump.
3. Resistance of the suction line
The more elbows, valves and other pipe fittings set in the suction line, the greater the resistance of the line. The larger the pump, the lower the inlet pressure of the pump. Therefore, try to reduce some unnecessary pipe fittings or increase the diameter of the suction pipe as much as possible to reduce the resistance of the pipeline, which can prevent the pump from cavitation.
