Slide 1
Low local pressure can form vapour bubbles
Cavitation begins when local liquid pressure falls low enough for vapor bubbles to form. It can occur even when the bulk liquid is not boiling.
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Vapor pressure depends on temperature. Heating the inlet liquid can reduce the pressure margin available to a pump, even if the piping and rotational speed stay unchanged.
Slide 2
Acceleration near the impeller can lower inlet pressure
Liquid accelerates as it approaches a pump impeller. Local pressure may fall to a lower level than the pressure measured farther along the inlet pipe.
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Restrictions, excessive suction lift or a low supply level can worsen the problem. Checking only the discharge pressure misses the conditions where the bubbles begin.
Slide 3
Collapse at higher pressure can erode the surface
When vapor bubbles enter a higher-pressure region, they can collapse violently. Repeated collapse near a surface can erode the impeller.
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The damage is not simply abrasion by solid particles. Small, intense local impacts can remove material over time and disturb flow, reducing performance while increasing vibration.
Slide 4
Available inlet head must exceed the pump’s need by a margin
Pump selection compares the inlet head available above vapor pressure with the head the pump requires. A practical margin is needed between them.
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Published required values depend on a defined performance criterion. Merely reaching a catalogue threshold does not guarantee the complete absence of bubbles or long-term damage.
Slide 5
Harder material does not remove the cause of cavitation
Improving the inlet route, changing operating conditions or selecting a suitable pump can reduce cavitation. Harder material alone does not remove its cause.
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Noise resembling gravel can be a clue, but diagnosis should combine sound with pressure, flow and inspection evidence. Other faults can also produce noise and vibration.
Sources
- Improving Pumping System Performance: A Sourcebook for Industry
U.S. Department of Energy