Cavitation in pumps:

meaning and useful tips to prevent it

When we talk about cavitation, especially in centrifugal pumps, we immediately think of “silent” damage and costly repairs. Understanding what cavitation really is and how to prevent it is essential for protecting the system: typical signs include reduced performance, unusual noises, vibrations, more frequent maintenance, and decreased energy efficiency.

In this article, we will look at what cavitation means, how to recognize it in time, and what strategies to adopt to avoid it.

What is cavitation in pumps?

Cavitation refers to the formation and subsequent implosion of vapor bubbles inside the liquid passing through the pump.

The phenomenon begins when, in an area of the circuit (often at the suction point or at the impeller eye), the pressure drops below the vapor pressure of the fluid. At that point, the liquid tends to “evaporate locally,” forming bubbles. The bubbles are then drawn towards areas of higher pressure where they collapse rapidly: these implosions generate micro-shocks that can damage the impeller and internal surfaces over time.

Main causes of cavitation

There are often multiple causes, which combine with each other. The most frequent are:

1) Local pressure too low compared to vapor pressure

If the pressure falls below the evaporation threshold of the fluid (even without heat input), bubble formation becomes likely. In centrifugal pumps, this typically occurs in areas with high fluid velocity, such as the impeller eye, where the pressure can drop rapidly.

2) Insufficient NPSH on suction

NPSH (Net Positive Suction Head) is the safety margin against cavitation.

NPSHa (available): NPSH available guaranteed by the system (actual suction conditions)
NPSHr (required): NPSH required by the pump (manufacturer’s data)

If NPSHa < NPSHr, the risk of cavitation increases
significantly. Good practice: always maintain a safety margin (do not operate at the limit).

3) High pressure drops on the suction line

The suction line is often the most critical point. Sharp bends, partially closed valves, small diameters, long pipes, or clogged filters cause pressure drops, insufficient hydraulic load, and therefore pressure drops before entering the pump. If the pressure drops below the vapor pressure, cavitation occurs.

4) High liquid temperature

As the temperature increases, so does the vapor pressure: the fluid “tends” to vaporize more easily. Therefore, for the same system, a hot liquid requires more favorable suction conditions than a cold one.

5) Operating conditions outside the design range (incorrect operating point)

If the pump operates far from the recommended point (e.g., due to changes in the system, valves, different flow rates required, etc.), internal conditions may worsen and instability and risks may increase, including cavitation (especially if suction is already borderline).

In practice

Cavitation = local evaporation due to excessively low pressure + nucleation (bubble formation) + implosion of bubbles when pressure rises.
This often occurs at the impeller eye.
Repeated implosions cause erosion and permanent damage.

Effects and damage caused by cavitation on pumps

Bubbles that collapse near surfaces generate shock waves and micro-jets that can cause micro-perforations, erosion, and material loss (especially on the impeller blades).

Typical consequences:

localized erosion on the impeller and volute
increased noise and vibrations
reduced flow rate and head
deterioration in efficiency and increased consumption
possible stress on seals and bearings (due to vibrations and instability)

How to recognize cavitation: 5 signs you shouldn't ignore

The first signs are often acoustic and mechanical:

sharp, intermittent noises, like “pebbles”
increasing vibrations
sudden drops in flow rate or pressure
fluctuations in power consumption
frequent wear/damage to seals and related components

Even “slight” noise should not be underestimated: it could be the onset of cavitation.

Solutions and prevention

Cavitation can be avoided through design choices and good operating practices. Monitoring pressure, flow rate, and absorption helps to detect the phenomenon before it causes damage.

Effective preventive measures:

ensure that NPSHa is always > NPSHr (with a margin)
reduce suction pressure drops (adequate diameters, fewer tight bends, clean filters)
position the pump as close as possible to the source and, where possible, with favorable suction
check the fluid temperature (especially if high)
avoid systematically operating off-point (pump/system curve)

Recommended operating practices

correctly size suction side pipes and accessories
keep filters and suction lines clean
limit sharp bends, restrictions, and “throttled” valves on the suction side
periodically check inlet pressure and NPSH conditions
use suitable materials and components in the most stressed areas (when necessary)

In summary

Cavitation requires attention both during design and operation. Small precautions, listening to signals, and proper maintenance extend the life of the pump and maintain high system performance.

At Fluimac, we support our customers in choosing and managing the most suitable pumps, simulating real working conditions to achieve consistent performance over time.