Cavitation in industrial pumps: understand this phenomenon

Have you ever heard of cavitation? Cavitation is a phenomenon characterized by vaporization and bubble formation caused by changes in pressure. Cavitation failures can affect the operation of pumps and, in some cases, totally compromise the equipment.

Read this article and find out more about cavitation, how to avoid it and how to solve this problem.

What is cavitation?

Cavitation is a hydrodynamic phenomenon that affects pumping systems and can lead to damage and equipment failure. It occurs when vapor bubbles form in a fluid flow, caused by reductions in pressure. Therefore, cavitation is the formation of bubbles from the vaporization of the liquid. Thus, cavitation typically occurs in the blade area of pumps or hydraulic turbines.

The pressure at the location where cavitation occurs can be equal to or lower than the vapor pressure, depending on the number and distribution of particles in the liquid, to which small gas or undissolved air bubbles can aggregate. Thus, these particles act as nucleation sites to initiate vaporization.

Additionally, the growth and implosion of these vapor bubbles, adjacent to solid surfaces, can cause serious erosion damage to the material surfaces. Since vaporization forms cavities, the term cavitation is used to describe the erosion and wear caused by the bubbles.

In summary, cavitation can be defined as the formation of partial vacuums in a liquid by a rapidly moving solid body or by very intense sound waves.

When proper maintenance is not performed, cavitation can cause damage to equipment, a decrease in productivity, and financial losses, inconveniences that can be avoided when the problem is identified in advance.

Cavitation in industrial pumps

Cavitation is a common effect in industrial pumps. When it occurs, the performance of the asset is reduced or even compromised.

As previously explained, cavitation in pumps occurs due to the decrease in pressure at the eye of the impeller, which is caused by the increase in fluid velocity. As a result, the fluid may undergo partial boiling at the pumping temperature. However, other factors can contribute to the appearance of a cavitation problem.

Causes of cavitation in industrial pumps

Cavitation issues in industrial pumps can begin due to the following factors:

• Reduction of pressure at the suction nozzle;
• Increase in flow velocity at the suction nozzle;
• Increase in the temperature of the pumped fluid;
• Layer separation in the flow or its reduction due to changes in the viscosity of the pumped fluid;
• Poor conditions in the suction piping, obstructions, or components causing excessive head loss;
• Additionally, the type of pump used may be inadequate for the service and thus experience cavitation.

Types of Cavitation

There are different types of cavitation, with the most common being suction cavitation and discharge cavitation. Each type can occur in different situations and present specific characteristics.

Suction Cavitation

Suction cavitation occurs when a pump is under low pressure or high vacuum conditions. When the fluid being pumped enters the eye of a centrifugal pump, the pressure is reduced. As a result, bubbles form in the impeller’s eye and move to regions of higher pressure, collapsing on the outer parts of the impeller.

Discharge Cavitation

This type of cavitation occurs when the pump’s discharge pressure is extremely high or when there are restrictions in the discharge flow and it cannot exit the pump. A very high discharge pressure causes a large portion of the pumped fluid to circulate inside the pump. Consequently, internal circulation is forced through the gap between the impeller and the pump casing at high speed, resulting in the formation of a low-pressure region and promoting cavitation.

How to Detect Cavitation in Pumps?

To prevent serious damage to the asset, it is essential to detect cavitation in pumps or other hydraulic equipment as quickly as possible. But how can this be done? When experiencing this problem, the machine may display some clear signs that can help maintenance managers to identify it.

Pay attention to the symptoms of cavitation in pumps

Pumps with cavitation problems exhibit some important signs that require attention, including:

Changes in vibration levels

Abnormal, unexpected vibrations or excessive vibration can indicate cavitation failure in pumps. Moreover, excessive vibration levels can also lead to premature failure of seals and mechanical bearings. In these cases, the energy released when vapor bubbles collapse can cause metal pieces to break and collide with other moving parts.

Noise

When facing a cavitation problem, the alert often comes in the form of noise, as if pumping stones. Again, the noise will be accompanied by vibration, reduced performance, or even a combination of all these characteristics. Therefore, at the first sign of unusual noises, conduct an investigation.

Weak flow or low-pressure

Cavitation in pumps can cause weak flow or low pressure of the pumped fluid, so noticing these signs is important to check the asset. 

Hot spots

It is not uncommon for the phenomenon of cavitation to cause some equipment components to heat up. Through a routine of sensitive inspection, it is possible to monitor these signs perceptible to human senses and requiring attention.

Increased energy consumption

Cavitation in pumps and other equipment can cause the equipment to consume more energy to operate. When abnormal energy consumption is noticed, it is necessary to investigate and understand the source of this variation, as the asset may suffer long-term damage.

Component erosion

Furthermore, one of the most common indications of cavitation in pumps is erosion of parts, especially the rotor. When experiencing cavitation, the interior of the equipment shows deep marks due to material erosion on the metal edges of the components.

Tips to avoid cavitation

Cavitation is something that can be avoided. Here are some guidelines to help control and prevent this problem:

• Observe the operational limits of the equipment and components;
• Create a phase diagram to determine the vapor pressure curve and thus avoid the combination of temperature and pressure that leads to liquid boiling;
• Check the positioning of the pump to ensure it does not affect suction;
• Observe and respect the specific aspects of each system;
• Make changes such as raising the liquid level in the suction tank or lowering the suction point;
• Select a type of valve with a lower-pressure drop

Solution to detect cavitation in pumps

Continuous monitoring solutions, meaning 24/7 monitoring of industrial pump health indicators, is the best way to prevent failures and problems such as cavitation. It also increases the reliability and availability of these assets.

Watch the video below to see how the Dynamox Solution assists in the management of industrial pumps, generating constant data that allows monitoring of asset performance, as well as identifying failures and improvement opportunities. In other words, with the solution, your assets operate efficiently and predictably!

The Dynamox Solution is capable of identifying early signs of cavitation, wear, and other potential pump failures, contributing to increased productivity levels and equipment optimization.

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