Cavitation in Pumps: A Comprehensive Guide to Hazards and Prevention Measures

I. What Is Pump Cavitation?

II. Key Hazards of Cavitation

1. Mechanical Damage (Most Direct Impact)

• Erosion of wetted components: High-frequency water hammer from bubble collapse repeatedly strikes metal surfaces of impellers, pump casings, and guide vanes. This leads to pitting, indentations, or even spalling (known as “cavitation erosion”). Over time, impellers may become unbalanced due to local damage, and in severe cases, they can fracture entirely.
• Fatigue failure of components: The constant high-frequency impact induces metal fatigue, weakening mechanical strength and shortening service life. For example, impellers may fail as fatigue cracks expand over time.

2. Diminished Pump Performance

• Reduced flow rate and head: Cavitation bubbles occupy space in the flow path, reducing the effective flow area and lowering liquid flow rates. Additionally, energy is wasted on bubble formation and collapse, decreasing the pump’s effective head.
• Significant efficiency drops: Energy that should drive liquid transport is diverted to bubble dynamics, leading to sharp efficiency declines (up to 30% or more in severe cases).

3. Compromised Operational Stability

• Noise and vibration: Bubble collapse generates high-frequency noise (typically 60–20,000 Hz) and pump vibration. This vibration can propagate to pipelines, causing loosening, leaks at connections, and instability in the entire system.
• Fluctuating operating conditions: Severe cavitation causes periodic surges in flow rate and pressure, making the pump unstable. This disrupts downstream equipment (e.g., erratic pressure in irrigation systems or interruptions in chemical processes).

III. Preventive Measures for Cavitation

1. Design-Stage Optimization

• Select appropriate pump types: Based on medium properties (temperature, viscosity, saturated vapor pressure), choose pumps with strong anti-cavitation performance (e.g., centrifugal pumps with double-suction first-stage impellers, inducers, or self-priming pumps). Inducers pre-raise liquid pressure, reducing cavitation risk at the impeller inlet.
• Optimize wetted component design:
  • Increase impeller inlet diameter and reduce inlet flow velocity to minimize local pressure loss.
  • Use streamlined impeller blades to avoid sudden flow channel contractions or turns, which reduce eddy currents (a common cause of local low pressure).
  • Use wear-resistant, impact-resistant materials (e.g., high-chromium cast iron, stainless steel, ceramic coatings) for wetted surfaces to enhance cavitation resistance.

2. Installation and Pipeline Design Optimization

• Control pump installation height: The vertical distance between the pump shaft and the suction liquid level is critical. Lower installation heights reduce suction line pressure loss, lowering cavitation risk. Calculate the “allowable suction vacuum height” or “net positive suction head (NPSH)” to determine the optimal height (formula: allowable installation height = allowable suction vacuum height – suction line head loss – safety margin).
• Optimize suction pipelines:
  • Use sufficiently large diameters (to limit flow velocity to 1–2 m/s) and reduce friction loss.
  • Keep pipelines short and straight, with fewer elbows, valves, or other local resistance components (use large-curvature elbows when necessary).
  • Ensure tight seals to prevent air leakage (air ingress lowers liquid pressure and accelerates cavitation).

3. Operational Controls

• Regulate liquid temperature: Higher temperatures increase saturated vapor pressure (e.g., water at 80°C has a vapor pressure of 47.34 kPa, vs. 2.34 kPa at 20°C), making vaporization more likely. Use cooling devices (e.g., heat exchangers) to keep temperatures in check.
• Avoid excessive flow rates: Operating beyond rated flow increases impeller inlet velocity and lowers pressure, triggering cavitation. Use valves or variable frequency drives to maintain operation near the rated condition.
• Stabilize suction liquid levels: Low liquid levels (e.g., in tanks or reservoirs) further reduce suction line pressure. Use level sensors to trigger automatic refills and maintain minimum levels.

4. Medium and Maintenance Management

• Remove dissolved gases: Gases (e.g., air) dissolved in liquids act as nuclei for cavitation bubbles in low-pressure zones. Install degassing devices (e.g., vacuum degassers) upstream of suction lines to reduce gas content.
• Regular maintenance:
  • Clean suction filters to prevent blockages and increased resistance.
  • Inspect wetted components for cavitation damage; repair minor pitting by polishing, and replace severely damaged parts promptly.
  • Maintain shaft seals (e.g., mechanical seals, packing seals) to prevent air or liquid leaks that cause pressure loss.

Summary