What To Do About Cavitation Of Centrifugal Pump

Jan 31, 2026

Cavitation is a common problem during the operation of centrifugal pumps, which can cause an increase in pump vibration and noise, a decrease in performance, and serious damage to components.

This article does not explore the professional theoretical knowledge of cavitation, but only attempts to use relatively simple language to provide a detailed introduction to several common types of cavitation in centrifugal pumps, the hazards of cavitation, and commonly used measures to improve cavitation on site.

1. Types of cavitation

From the location of occurrence, cavitation can be divided into blade cavitation, gap cavitation, rough cavitation, cavity cavitation, and backflow cavitation.

 

(1) Foliar cavitation

 

When cavitation occurs, the formation and bursting of bubbles mainly occur on the front and back of the blades, also known as airfoil cavitation, which is the main form of cavitation in centrifugal pumps. When the pump is installed too high, even if the pump is running under design conditions, a low-pressure area is prone to occur on the back of the blade inlet and outlet:

 

 

1) When the pump operates under high flow conditions, flow separation and vortices occur on the leading edge of the blades, creating negative pressure that may cause cavitation on the front of the blades.

2) When the pump operates under low flow conditions, vortices are generated on the back of the blades, creating a low-pressure zone and causing cavitation on the back of the blades.

 

(2) Gap cavitation

 

It refers to the cavitation formed when the liquid flows through a narrow channel or gap, causing a local increase in flow velocity and a decrease in pressure to the vaporization pressure of the flow components.

At the gap between the wear-resistant ring of the centrifugal pump casing and the outer edge (cover plate) of the impeller, under the pressure difference (especially large pressure difference) on both sides of the impeller inlet and outlet, the liquid on the outlet side flows back at high speed, causing local pressure drop and cavitation

In the small gap between the outer edge of the axial flow pump blades and the pump casing, under the action of the pressure difference between the front and back of the blades, the high reverse flow velocity of the liquid in the gap can also cause local pressure drop, resulting in cavitation at the corresponding outer edge of the blades in the pump casing, and forming a honeycomb and rough surface cavitation zone at the outer edge of the impeller and blades.

 

(3) Rough cavitation

 

Rough cavitation refers to the generation of vortices downstream of protrusions when liquid flows through the uneven surface of rough flow components inside the pump casing, causing a local pressure drop and leading to cavitation.

During the casting and processing of pump flow components, surface unevenness, sand holes, air holes, etc. may cause sudden changes in local flow state and result in cavitation.

 

(4) Cavity cavitation

 

Cavitation in a cavity refers to the formation of a spiral vortex band in the suction chamber at the inlet of a pump due to poor water inlet conditions or insufficient submergence depth. When the central pressure of the vortex belt decreases to the vaporization pressure, cavitation will also occur, accompanied by strong vibration.

 

(5) Reflux cavitation

 

Generally speaking, the prerequisite for cavitation is NPSHa<NPSHr, which means that the cavitation allowance of the device is less than the necessary cavitation allowance of the pump. However, there is a special case where cavitation occurs when NPSHa>NPSHr, known as backflow cavitation. Due to its occurrence when operating below the design flow point, it is also known as low flow cavitation.

When the pumping flow rate is too low or the inlet pressure is too high, backflow occurs. When the pumping flow rate is too low, internal reflux occurs at the inlet of the impeller; When the inlet pressure of the pump is too high, internal reflux occurs at the outlet of the impeller. Internal reflux causes an increase in liquid flow rate until vaporization produces bubbles, which then rupture under higher surrounding pressure. When internal backflow occurs at the suction port, irregular crackling noise will be emitted around the suction port of the pump, accompanied by high-intensity detonation sound.

 

 

Reflux cavitation can generally be improved through the following methods:

1) Increase the output flow rate of the pump.
2) Install a bypass between the inlet and outlet of the pump (this method is difficult for customers to accept in practical applications).
3) Optimize the structure of the impeller (reduce the inlet area of the impeller).

 

2. The hazards of cavitation

(1) Performance degradation, pipeline damage

 

Cavitation can significantly reduce the performance of the pump. Usually, for centrifugal pumps, when the inlet pressure drops to a certain extent, their performance will sharply decrease, which is also known as cavitation fracture. Cavitation can also cause instability inside the fluid, which can lead to oscillations in flow and pressure. With the assistance of these oscillations, it may cause damage to the pump and its inlet and outlet pipelines.

 

(2) Serious damage to the overcurrent components of the pump

 

Cavitation can cause damage to the surface of components. When bubbles burst, the surrounding liquid generates extremely high impact pressure (peak pressure) of up to 49 MPa. When the hydraulic strength of cavitation exceeds the material's ability to resist this impact, it can lead to local wall material fatigue failure and surface material detachment. Cavitation occurs simultaneously with chemical and electrochemical corrosion. The size of the pits generated by corrosion and plastic deformation of materials in the early stage of cavitation is about 10 μ m to 50 μ m, especially for some materials with poor corrosion resistance, which may exhibit honeycomb like structures under long-term cavitation.

 

(3) Generate vibration and noise

 

At the moment when the bubble condenses, shrinks, and ruptures, the liquid around the bubble fills the void at high speed (formed by the condensation and rupture of the bubble), generating pressure pulsations and thus exciting vibration and noise. The frequency of cavitation noise is generally between 10 kHz and 100 kHz, while the frequency of cavitation noise caused by reflux and pressure pulsation is around a few hundred Hz, which makes the human ear particularly sensitive. At the same time, cavitation can also stimulate vibration, and the main frequency of vibration generated by cavitation is generally around 1 kHz.

Cavitation is not only characterized by high noise levels, but also by vibration indicators such as insufficient stiffness of the pump base and poor pipeline support, which can cause structural resonance; After the installation of the pump, the base is filled with concrete, and the support stiffness of the pipeline is sufficient, which generally does not cause strong vibration phenomena. However, through vibration measurement on the pump body, the high-frequency component of the vibration frequency generated by cavitation is dominant, and the acceleration value of the vibration is higher than the vibration displacement and vibration velocity.

 

3. Common measures to improve cavitation performance

(1) Measures to improve the anti cavitation performance of centrifugal pumps themselves

 

1) Improve the suction port design of the pump

By grinding the impeller, the flow area can be increased;

Increase the curvature radius of the inlet section of the impeller cover plate to reduce the rapid acceleration and pressure drop of the liquid flow;

Reduce the thickness of the blade inlet appropriately and round the blade inlet (polish the blade head, sharpen it to reduce the impact loss of the inlet and reduce the sensitivity of the inlet angle, and the necessary cavitation allowance can be reduced by about 0.5 meters), making it close to a streamline shape, and also reducing the acceleration and pressure drop around the blade head;

Improve the surface smoothness of the impeller and blade inlet to reduce resistance loss;

Extend the blade inlet edge towards the impeller inlet to allow the liquid flow to receive work in advance and increase pressure.

 

2) Add a front induction wheel

Make the liquid flow do work in advance in the front induction wheel to increase the liquid flow pressure (this scheme requires structural changes and recalibration of various design parameters).

3) Adopting double suction impeller

Increase the inlet area of the impeller and reduce the inlet liquid flow rate (decrease in flow rate and increase in pressure).

4) Using a slightly larger positive angle of attack

To increase the blade inlet angle, reduce the bending at the blade inlet, minimize blade blockage, and thus increase the inlet area;

Improve working conditions under high flow conditions to reduce flow losses. But the positive angle of attack should not be too large, otherwise it will affect efficiency.

5) Using a low-speed pump

The lower the rotational speed, the smaller the NPSHr.

6) Using anti cavitation materials

Practice has proven that the higher the strength, hardness, and toughness of a material, the better its chemical stability, and the stronger its resistance to cavitation.

 

(2) Measures to increase the cavitation allowance of the device

 

1) Increase the pressure of the liquid level in the storage tank before the pump to improve the effective cavitation allowance.

2) Reduce the installation height of the pump in the suction device, especially when conveying hot water as the medium, and consider the relationship between the suction height and the medium temperature.

3) Replace the suction device with a backflow device.

4) Reduce flow loss in the suction pipeline before the pump. If possible, shorten the pipeline within the required range, use appropriate suction pipeline diameter and filter filtration area (if any) to reduce the flow rate in the pipeline, reduce the number of bends and valves, and increase the valve opening as much as possible.

5) If the gap cavitation is severe, the method of drilling balance holes on the impeller can be adopted to reduce the leakage flow rate and alleviate the degree of cavitation. The balance holes on the blades have a destructive and interfering effect on the injected liquid flow at the impeller inlet. The area of the balance holes should not be less than 5 times the clearance area of the sealing ring to reduce the leakage flow rate, thereby reducing the impact on the main liquid flow and improving the pump's anti cavitation ability.

6) Experience has shown that starting from the mechanism of cavitation, supplementing an appropriate amount of gas to the suction port can disrupt the conditions for cavitation to occur. However, using air replenishment to prevent pump cavitation is highly technical, and only with appropriate air replenishment volume, location, and method can good results be achieved. Otherwise, it will cause a significant decrease in the flow rate, head, and efficiency of the pump, and even lead to flow interruption and adverse consequences during operation.

 

 

Considering the difficulty in controlling the appropriate amount of air supply and accurate measurement, combined with the author's practice, it is recommended to use a needle valve that can adjust the flow rate for the air supply valve. During on-site adjustment, cavitation noise can be used to distinguish: adjust the intake volume through the needle valve until cavitation noise is minimized (some systems can completely eliminate noise, but some systems can only reduce cavitation noise, not completely eliminate it), then adjust the needle valve back a little to reduce the intake volume, observe operation for a period of time until no performance abnormalities occur under various specified operating conditions, and then lock the opening of the needle valve. This method should never lower the sound to the lowest level! If the inlet pressure is positive when the pump stops running, a check valve should be installed to prevent leakage. 

7) Research has found that when the medium contains volatile gases and solid particles such as sand, the cavitation performance of the pump will decrease. To ensure that the pump does not experience cavitation, the suction height of the pump should be reduced by at least 4.2 meters from the calculated height of the clean water. This is worth paying attention to in the municipal industry.