Cavitation in Hydraulic Systems: Internal Destruction

After oil contamination, cavitation is one of the most common causes of damage in hydraulic systems. It occurs when hydraulic components are not optimally matched or when module limits are not observed.

What is Cavitation?

The word “cavitation” contains “cavern” or “cavity,” which means “hollow space.” Cavitation refers to the spontaneous formation of cavities in the hydraulic medium. These cavities appear in the form of bubbles. Since these bubbles contain a vacuum, they immediately collapse again. This releases large forces abruptly, which spread in the form of shock waves around the collapsing bubble. These shock waves are the cause of the destructive effect of cavitation.

Causes of Cavitation

Hydraulics is the study of transmitting forces through a fluid. For optimal operation of the hydraulic system, the fluid line must not be interrupted at any point. The basis of hydraulics is the incompressibility of liquids.

To ensure that the fluid (usually hydraulic oil) remains bubble-free, it requires transitions that are as smooth and flow-optimized as possible. Where the flowing medium passes through non-flow-optimized transitions at high pressure, cavitation can occur. The fluid flow tears apart, and bubbles form, which immediately collapse again. Propellers, nozzles, orifices, and pumps are particularly affected by cavitation.

Consequences of Cavitation

Cavitation has two direct and one indirect consequence. These are:

• Noise generation at the point of cavity formation
• Change in the flow behavior of the medium, for example, oscillating pressure
• Damage to components or the line

The constantly forming and collapsing bubbles generate permanent popping noises. In practice, this is perceived as a “crackling noise.” This noise is easily localizable.

Bubble formation changes the flow behavior by reducing the incompressibility of the medium. Pressure is no longer reliably and uniformly transmitted in the hydraulic oil. These pressure fluctuations can trigger malfunctions in valves and sensors.

However, much more serious is the erosion caused by the pressure waves of the collapsing bubbles. These can damage internal components so severely that it leads to the failure of the entire system.

Countermeasures against Cavitation

Hydraulic systems operate under high working pressure. To maintain this, powerful pumps with equally strong drives are required. The motors used are usually so loud that cavitation is not immediately noticed.

To detect cavitation as quickly as possible, even in noisy environments, the industry has developed special cavitation sensors. These consist of a sound and a vibration sensor. The sensor can also be well connected to a control system via modern control technology. For example, pump performance can be reduced in the event of cavitation to avoid consequential damage as quickly as possible.

Hydraulic systems require powerful filtration and regular oil changes. It is advisable to take a sample for analysis with each change. Depending on the particles present in the oil, cavitation can also be inferred.

Fundamentally, however, the formation of cavitation always means that a system was incorrectly designed or operated outside its technical parameters. If the cavitation problem cannot be resolved by adjustments, the system must be partially or even completely overhauled.