Glossary term
Cavitation
The formation, growth, and collapse of vapor cavities in a liquid when local pressure falls near or below the liquid vapor pressure.
Definition
phenomenonThe formation, growth, and collapse of vapor cavities in a liquid when local pressure falls near or below the liquid vapor pressure.
Cavitation is a fluid-dynamic and damage mechanism. It can reduce pump performance, create noise and vibration, erode surfaces, disturb flow measurement, and damage propellers, valves, turbines, injectors, and hydraulic machinery.
Cavitation occurs when local liquid pressure falls low enough for vapor cavities to form. When those cavities move into regions of higher pressure, they can collapse violently. The collapse generates pressure pulses, noise, vibration, microjets, and local surface damage.
Engineering role
Cavitation is important in pumps, propellers, turbines, hydrofoils, valves, injectors, bearings, piping restrictions, and hydraulic systems. It can reduce head, flow rate, efficiency, and controllability. In severe cases it erodes metal, damages coatings, loosens material, accelerates fatigue, and produces a distinctive rattling or gravel-like sound.
Pressure and vapor pressure
The condition for cavitation depends on local absolute pressure, not gauge pressure alone. The relevant comparison is with vapor pressure at the actual liquid temperature. Higher temperature raises vapor pressure and can make cavitation more likely. In pump systems, engineers often use net positive suction head (NPSH) to compare available suction conditions with the pump manufacturer’s required value.
Design and diagnosis
Mitigation includes increasing inlet pressure, reducing suction losses, lowering liquid temperature, selecting a different pump, reducing speed, improving inlet geometry, avoiding sharp restrictions, and choosing materials or coatings with better erosion resistance. Diagnosis may use vibration, acoustic emission, performance curves, pressure measurements, visual inspection, and surface damage patterns.
Cavitation versus flashing
Cavitation should be distinguished from flashing. In cavitation, vapor bubbles collapse when pressure recovers. In flashing, the fluid remains partly vaporized downstream because pressure stays below vapor pressure. The damage, noise, and control implications can be different, especially in valves and process equipment.
Common mistakes
Common mistakes include checking only discharge pressure, using gauge pressure without converting to absolute pressure, ignoring temperature effects, and assuming cavitation is only a pump problem. Another error is oversizing a pump and then throttling it into an operating region where recirculation, vibration, or cavitation becomes worse.