Cavitation is one of the most common phenomena that shorten the service life of centrifugal pumps—both in household installations and in large industrial and agricultural systems. In our earlier article What Is Cavitation and How to Prevent It, we explained the fundamentals of this phenomenon. In this text, we take it a step further—as a manufacturer of IBO and IPRO water pumps, we show how to identify cavitation in practice during operation, how to calculate the NPSH margin when designing a suction installation, and which equipment components—controllers, variable-frequency drives, valves, filters, and pressure gauges—actually help reduce the risk of its occurrence. The text is aimed primarily at installers and service technicians who select and commission centrifugal pumps on a daily basis.
Cavitation in centrifugal pumps—what happens inside the impeller
The formation of cavitation in a centrifugal pump has a very specific physical cause. When the liquid enters the impeller inlet, its flow velocity increases sharply and, in accordance with the Bernoulli principle, the liquid pressure at this point drops. If the fluid pressure falls below the saturation vapor pressure of the liquid at a given temperature, local vaporization occurs—tiny vapor bubbles appear in the liquid. This moment—the liquid pressure falling below the vapor pressure—is the starting point of the entire cavitation phenomenon.
Vapor bubbles cause a local disruption in the continuity of the liquid stream, but the real problem appears a moment later. The pump impeller transfers the pumped liquid from a low-pressure area (the suction side) to a higher-pressure area (the discharge side). When the vapor bubbles enter the higher-pressure area, they undergo a rapid implosion—their collapse occurs at a speed comparable to microscopic hydraulic impacts. The energy released during this process is so great that, when repeated thousands of times per minute, it causes erosive cavitation damage to the material on the surface of the impeller and pump casing.
It is worth remembering the relationship: the lower the saturation pressure of a given liquid under the installation’s operating conditions, the smaller the pump’s safety margin. Therefore, the temperature of the pumped liquid directly affects how easily the vaporization threshold is exceeded.
Gas cavitation versus classic vapor cavitation – two different mechanisms
In installation practice, it is worth distinguishing between two phenomena that are often confused. Classic vapor cavitation occurs when the pressure drop is sufficient for the liquid to evaporate locally inside the pump – this is the mechanism described above. Gas cavitation has a different cause: the release of gases dissolved in the liquid, most often air, as a result of a pressure drop, without the need to reach the saturated vapor pressure. Both phenomena produce similar effects – pressure fluctuations, reduced capacity, and noise – but their underlying causes differ, and consequently, so do the methods of preventing them.
Gas cavitation most often occurs when there are leaks in the suction pipeline, allowing air to enter the installation, and when the flow rate is improperly matched to the pipe diameter. Classic vapor cavitation, in turn, is closely linked to the operating conditions on the pump suction side – suction lift, medium temperature, and flow resistance.
What increases the risk of cavitation in an installation – the pump suction side under scrutiny
The vast majority of cavitation cases in installation practice originate on the pump suction side rather than the discharge side. The most common causes that increase the risk of cavitation include:
- Excessive pump suction lift – the deeper the pump must draw the liquid, the lower the static pressure on the suction side, and therefore the smaller the margin above vaporization pressure.
- Suction pipeline that is too long or too narrow – causes pressure losses proportional to the square of the flow velocity, further reducing the pressure at the impeller inlet.
- Elevated liquid temperature – as the temperature rises, the saturated vapor pressure increases, reducing the safety margin even with the same installation geometry.
- Air leaks on the suction side – typical of suction installations with threaded connections or worn seals.
- Excessive flow rate relative to the pump parameters – operation outside the performance curve, with a capacity far exceeding the optimum point.
In practice, this means that a centrifugal suction pump operating with a long suction pipeline, at an elevated medium temperature and with a high suction lift, is much more exposed to cavitation zones than the same pump supplied from a tank located close to the system level. By selecting submersible pumps instead of surface suction pumps, the suction-side problem can often be eliminated entirely – the impeller then operates fully submerged in liquid, significantly reducing the risk of pressure dropping below the vapor pressure. Our overview of IBO submersible pumps presents solutions used in precisely such more hydraulically challenging applications.
NPSH, NPSHav and NPSHr – how to design pumps resistant to cavitation
The most important parameter for assessing the risk of cavitation at the system design stage is NPSH (Net Positive Suction Head), i.e. the suction pressure head above the liquid’s vapor pressure. The technical documentation for centrifugal pumps contains two values that must be compared:
- NPSHav (available) – the available pressure head, resulting from the specific system: suction lift, suction-pipe length, liquid temperature, and atmospheric pressure at the installation site.
- NPSHr (required) – the required pressure head, specified by the pump manufacturer for a given operating point on the performance curve. This value results from the design of the impeller and the configuration of the centrifugal pump used in the model.
The basic principle every installer should know is that pumps should be designed so that NPSHav is always clearly higher than NPSHr – in practice, a safety margin of around 0.5–1 meter of liquid head is recommended. If this condition is not met, pump operation will almost inevitably lead to cavitation, regardless of how high-quality the centrifugal pump itself is. Therefore, when selecting surface pumps or submersible pumps for a specific system, calculating the actual NPSHav for the operating conditions should come before choosing a specific model, not the other way around.
Symptoms of cavitation during pump operation
Cavitation can be detected before permanent damage occurs to the pump components. Typical symptoms include:
- a characteristic noise resembling a pump conveying gravel or small stones – this is the sound of vapor bubbles imploding,
- increased vibrations of the pump casing and pipeline, exceeding the normal operating level,
- uneven, pulsating pump operation and pressure fluctuations visible on the discharge-side pressure gauge,
- a noticeable drop in pump performance despite unchanged system parameters,
- faster-than-usual rise in bearing and mechanical seal temperatures.
Installing a pressure gauge on the pump's suction and discharge sides is one of the simplest diagnostic tools – a sudden, recurring pressure drop on the suction side often precedes audible signs of cavitation by several hours or days of system operation.
Effects of cavitation – damage to pump components
Prolonged operation under cavitation conditions leads to permanent, costly pump damage. The most characteristic damage is so-called cavitation pitting – irregular, sponge-like material losses on the impeller surface, in places where vapor bubble implosion occurs most intensely. In advanced cases, cavitation damage also affects the pump casing around the flow channels.
Cavitation rarely occurs in isolation – it is usually accompanied by additional effects:
- accelerated wear and leakage of the mechanical shaft seal resulting from vibrations and local pressure changes,
- damage to the motor bearings caused by vibrations transmitted to the shaft,
- reduced pump performance and increased electricity consumption in relation to the results achieved,
- in extreme cases – complete loss of impeller flow capacity and the need to replace it.
Importantly, damage to pump components caused by cavitation is usually not covered by the manufacturer's warranty, as it results from incorrect system selection or operation rather than a manufacturing defect in the device. This makes preventing the phenomenon at the design and commissioning stages all the more worthwhile.
How to prevent cavitation in practice – equipment and system selection
Effectively reducing the risk of cavitation rarely comes down to a single action – it usually involves combining the right pump selection with suitable installation equipment. Alongside circulation, circulating, submersible, deep-well and surface pumps from the IBO and IPRO brands, our range includes components that directly support stable, cavitation-free system operation:
- Variable frequency drives (frequency converters) – by adjusting the pump motor speed to the current water demand, they limit pump operation at performance points where the risk of cavitation is greatest. We explain more about how they work in the article Submersible pump – types, installation and benefits of a variable frequency drive, while specific models and accessories can be found in the variable frequency drives and accessories section.
- Pump controllers – monitor pressure and operating parameters in real time, switching off the pump before prolonged operation under cavitation or dry-running conditions occurs. Dry running, which is closely related to cavitation, is described in greater detail in the article What is pump dry running and how can you protect against it?.
- Check and shut-off valves – when properly selected and installed on the suction pipeline, they reduce the risk of air pockets forming and sudden pressure drops when the pump starts.
- Filters – installed on the suction side, they prevent solid contaminants from entering the impeller, thereby indirectly protecting working surfaces already weakened by cavitation from additional mechanical erosion.
- Pressure gauges – enable ongoing monitoring of pressure on the suction and discharge sides, allowing the first symptoms of cavitation to be detected long before audible and visible damage occurs.
When selecting a specific model, it is also worth consulting our general guide Dambat water pumps – a guide to types and applications (IBO / IPRO), which helps match the pump type to the nature of the installation even before calculating the NPSH parameters.
Selecting a pump for a specific application – what to consider
When designing or modernizing an installation, it is worth remembering that simply choosing a brand or motor power is not enough if the hydraulic balance of the suction side is overlooked. The recommended sequence of steps when selecting a cavitation-resistant pump is as follows:
- Determine the pump’s actual suction lift, as well as the length and diameter of the suction pipeline in the specific installation.
- Calculate the pressure losses resulting from flow resistance, elbows, valves, and the length of the suction line.
- Determine the temperature of the pumped liquid and read the corresponding saturated vapor pressure from the tables.
- Determine the available NPSHav for the installation and compare it with the NPSHr value specified by the manufacturer for the intended operating point.
- If the margin is too small, consider relocating the pump (e.g., installing a submersible model instead of a surface-mounted one), shortening the suction pipeline, or using a model with a lower NPSHr.
The range includes models intended for domestic applications as well as solutions for agricultural and industrial installations—including IBO surface pumps for shallow water intakes and deep-well pumps designed for deep wells, where correctly calculating the suction lift is particularly important. If you have any doubts, our technical department will be happy to help you select a model for your system’s specific parameters.
Frequently asked questions (FAQ)
How does cavitation differ from normal pump operating noise?
The operating noise of a pump is usually constant and steady, whereas the sound accompanying cavitation resembles gravel or small stones being pumped—it is irregular and appears suddenly, most often when the pump’s operating point changes, for example when water consumption increases.
Can cavitation occur in a submersible pump?
The risk is significantly lower than in surface-suction pumps because the impeller operates submerged in liquid, eliminating the problem of suction lift. However, cavitation can occur in submersible pumps when the pump operates close to the water surface level or when the flow rate is too high for the source’s capacity.
How quickly does cavitation damage a pump?
It depends on the intensity of the phenomenon. With a slight, periodic exceedance of NPSHr, the first signs of erosion on the impeller may appear after several months of operation. With severe, continuous cavitation, serious damage to pump components may occur after just several to several dozen hours of operation.
Does a variable frequency drive completely eliminate the risk of cavitation?
A variable frequency drive limits pump operation at unfavorable points on the performance curve and helps maintain stable pressure, but it does not replace proper design of the suction side. If the system’s NPSHav is significantly below the pump’s NPSHr, adjusting the motor speed alone will not eliminate the problem.
How important is water temperature for the risk of cavitation?
As the liquid temperature rises, the saturated vapor pressure increases, reducing the available NPSHav margin. Therefore, the same system that operates safely with cold water may generate cavitation zones when the medium temperature is elevated.
Is a pressure gauge enough to diagnose cavitation?
The pressure gauge on the suction and discharge sides is a very helpful diagnostic tool, showing pressure fluctuations typical of cavitation, but a complete diagnosis should also include observing noise and vibrations and analyzing the system parameters (suction lift, pipeline length, liquid temperature).
