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Cavitation and Aeration in Hydraulic Systems

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Hydraulic pumps are a ubiquitous part of the manufacturing and industrial sectors. They harness the immense pressures generated by the movement of fluids, in order to accomplish a wide range of tasks. Hydraulic systems continue to see regular use thanks in large part to the fact that they can be customized to yield virtually any desired amount of torque and speed.
Of course, even the best maintained hydraulic systems may develop problems as time goes on. Two of the most common issues - cavitation and aeration - can present difficulties in that they result in similar symptoms. If you would like to learn more about troubleshooting a hydraulic system, read on. This article will discuss the difference between cavitation and aeration.


Cavitation refers to the phenomenon of air bubbles forming inside of the system's fluid, as well as the negative effects of such air bubbles. As these air bubbles flow deeper into the system, they are subjected to fast pressure changes, which cause the bubbles to implode. The force of these implosions can be large, leading to stress and wear on a variety of internal components.
In its most literal sense, cavitation denotes the pitting that the implosion of air bubbles has on metal surfaces inside of the hydraulic system. Small cavities on the walls of metal components make them more susceptible to fatigue and, ultimately, failure. Cavitation tends to be caused by an inability of the pump to draw in enough fluid to match the intake volume.
This inability may be caused by filter restrictions or other impediments to proper flow. Because the hydraulic fluid cannot pass into the pump with the requisite velocity, air bubbles are pulled out of it instead. These bubbles then flow further into the system where they lead to the aforementioned implosions.
Cavitation can manifest as a variety of symptoms, including sluggish operation, lower system pressure, and excessive fluid temperatures. The most noticeable sign of cavitation, however, will be a persistent high pitched sound. Often described as a whining or whirring sound, this is the sound produced by the implosion of all the tiny air bubbles.


Aeration can be easily confused with cavitation, thanks to the fact that aeration will lead to virtually the same set of performance symptoms: low pressure, high temperature, and so on. Aeration also involves the undesirable presence of air bubbles inside of the pump system. The chief difference, however, lies in the manner by which these air bubbles gain entry.
Aeration involves air that has been sucked into the system upstream from the pump. Because of the vacuum induced by the pump, the pressure inside of the upstream half of the system tends to be lower than the normal pressure of the atmosphere. In a well-maintained system, all components will be tightly sealed, meaning that no air can possibly be sucked in as a result of this negative pressure differential.
But as systems age, fittings tend to work loose. Likewise, seals may fail as the result of constant exposure to changes in pressure. Either of these scenarios may create enough of a gap between components that air can be sucked into the system.
As noted above, the symptoms produced by aeration make it easily confused with cavitation. A savvy technician can often tell the two apart by means of the sounds they produce. Like cavitation, aeration will also result in a high pitched sound: the sound of air entering the system through a narrow crack.
Yet the sound of aeration tends to be somewhat more complex. The high whining is frequently accompanied by a rattling sound, as though gravel were being jostled about inside of the system. Likewise, aeration will also cause the fluid in the reservoir to appear especially foamy and opaque.
For more information about diagnosing and repairing common problems faced by hydraulic systems, please don’t hesitate to contact the experts at Anything On-Site Repair.