Cavitation is the formation and sudden collapse of vapor-filled cavities (cavitation bubbles) in a liquid, triggered by local pressure drops. In pumps, this process leads to damage, loss of performance, and significant operating noise.
What is Cavitation?
Cavitation is one of the most critical phenomena in pump technology and always occurs when the local pressure in the pumped medium falls below the vapor pressure of the liquid. Tiny vapor bubbles form at these points, which later collapse again as soon as the pressure in the flow increases. This collapse generates micro shock waves with very high local energy densities, which literally “abrade” metallic surfaces. Impellers, housings, and inlet areas in centrifugal pumps are particularly affected.
How does Cavitation occur in a Pump?
The most common cause is insufficient pressure at the pump inlet, often indicated by deviations in the NPSH (Net Positive Suction Head) value. If the required NPSHr of the pump is not covered by the available NPSHa, the pressure at the inlet drops so sharply that vapor bubbles form. Unfavorable pipe routing, suction lines that are too small, dirty filters, high pumped medium temperatures, and excessive speeds also promote the occurrence of cavitation.
The flow velocity increases rapidly, especially in the impeller. As soon as the bubbles collapse in the higher pressure area, extreme point loads act on the material. These can become visible as typical “cavitation pitting” – a surface that looks as if it has been perforated by many small craters.
What are the Consequences of Cavitation?
Cavitation affects pumps in several areas:
- Material damage: pitting, erosion, and loss of material thickness.
- Noise: a clearly audible hissing, rattling, or crackling sound.
- Increased vibration: mechanical stresses increase, bearings and seals suffer.
- Loss of efficiency: The flow rate can drop, and the pump becomes unstable.
- Reduced service life: In the long term, massive damage and even total failure can occur.
Cavitation is therefore not just a theoretical phenomenon, but an economically relevant factor in plant operation.
How can Cavitation be avoided?
To avoid cavitation in pump systems, pressure conditions, flow resistance, and operating parameters must be optimally coordinated:
- Ensure that NPSHa ≥ NPSHr
- Keep the suction line short, straight, and with a generous diameter
- Regularly check suction-side fittings, filters, or backflow preventers
- Keep the pumped medium as cool as possible → lower vapor pressure
- Adjust the pump speed (especially when operating with a frequency converter)
- Select a suitable impeller or pump with a favorable NPSH curve
- Install a pre-chamber or storage tank to stabilize the pressure
In industrial applications, cavitation is increasingly being predicted using CFD (computational fluid dynamics) simulations in order to identify design weaknesses at an early stage.
Why is Cavitation an important Issue?
Cavitation has a direct impact on efficiency, plant maintenance costs, and operational safety. Since pumps are used worldwide in almost all industrial sectors—chemical, petrochemical, water/wastewater, food, mechanical engineering—understanding the phenomenon is a fundamental element for anyone who designs, operates, or plans pumps.
