Cavitation in Pumps: Causes, Effects and How to Prevent It

What Is Cavitation?

Cavitation happens when pressure within the pump drops below the liquid’s vapour pressure, causing bubbles to form. As these bubbles travel into higher-pressure zones, they collapse violently and generate shockwaves that can pit and erode pump components. These pressures can reach extremely high levels, leading to serious damage over time.

Causes of Cavitation

• Insufficient Net Positive Suction Head (NPSH)
  Cavitation typically occurs when the available NPSH (NPSHᴬ – how much push the liquid already has) is lower than the pump’s required NPSH (NPSHʳ – how much push the pump needs). NPSHᴬ depends on system conditions, such as tank level, pipework losses, and vapour pressure. NPSHʳ is provided by the pump manufacturer and defined as the suction head at which the pump’s delivery head drops by 3 percent.
• High Pump Speed
  Running pumps at excessive speeds increases flow velocity and can reduce suction pressure, promoting bubble formation.
• Poor Suction Pipework Design
  Long suction lines, sharp bends, small inlet pipelines or blockages can cause pressure losses, reducing NPSHᴬ.
• Operating Off the Best Efficiency Point (BEP)
  Operating far from the pump’s BEP (especially below 10 per cent) can lead to discharge cavitation, where fluid circulates internally and vapour forms due to local wake conditions.
• High Fluid Temperature
  Elevated temperature increases vapour pressure, making cavitation more likely even at modest pressure drops.

Signs of Cavitation

Pump impeller affected by cavitation.

Noise: Often described as sounding like gravel or marbles passing through the pump casing. Vibration: Cavitation causes intense vibration, which may damage bearings, seals and shafts. Reduced Performance: You may observe a drop in flow rate, discharge pressure or head, and increased power draw under unstable conditions. Physical Damage: Persistent cavitation can lead to pitting, chipping or erosion of impellers and casings. Debris in Discharge: In extreme cases, fragments from worn components such as seals or bearings may appear in the pumped fluid.

How to Prevent Cavitation

1. Maintain Adequate NPSH Margin
   Ensure that NPSHᴬ ≥ NPSHʳ + safety margin (commonly around 0.5 – 1 metre, sometimes up to 1.5 metres).
2. Optimise Suction Conditions
   Raise the fluid source level or lower the pump to increase static head.
   Minimise suction line length, enlarge pipe diameter, and avoid sharp bends or restrictions.
   Keep the strainer and filters clean to reduce friction losses.
3. Manage Pump Speed
   Reduce rotational speed when possible. This lowers NPSHʳ and helps maintain conditions above catalytic thresholds.
4. Select Suitable Pump Size and Type
   Choose pumps whose performance curves fit the application and maintain adequate NPSH conditions under all operating circumstances.
5. Temperature Control
   If fluid temperature is high, consider cooling or insulation to reduce vapour pressure and minimise cavitation risk.
6. Regular Inspection and Maintenance
   Monitor for unusual noise, vibration or performance drop. Early detection and correction, such as cleaning pipework or adjusting operation, can prevent long-term damage.

Summary Table

Final Thoughts

Cavitation is a serious but preventable issue when addressed from the design stage through operation and maintenance. At TF Pumps, we help ensure your system is correctly specified and optimised to avoid cavitation risks and maintain long-term reliability.

Additional Reading

How Do Centrifugal Pumps Work?
Friction Loss – What is it and how do I calculate it?
British Pump Manufacturers Association (BPMA): Cavitation Resources
Understanding Axial, Radial and Mixed flow Types