CAVITATION Cause and Effect The word cavitation is a process that a Hydraulics Technician does not want to encounter. Cavitation can occur due to entrained air bubbles in the hydraulic fluid or vaporization of the hydraulic fluid. This occurs when the suction lift is excessive and the inlet-pressure falls below the vapor pressure (pressure which a liquid starts to boil and thus begins changing into vapor) of the liquid. As a result, air or vapor bubbles, which form in the low-pressure inlet region of the pump, are collapsed when they reach the high-pressure discharge region. This produces high fluid velocity and impact forces, which can erode the metallic components and shorten pump life.
Example Cavitation is the formation and collapse of vapor bubbles by means of mechanical force. This process will cause damage to internal pump components by flaking or pitting the surface of those components. The tiny flakes or particles of metal move downstream of the pump and enter other parts of the hydraulic system, causing damage to the other components in the system. Cavitation will also prevent proper lubrication of mating internal components of the hydraulic system. This is caused when the air bubbles move between the mating parts, instead of the lubricating fluid. Analogy and Explicit Terms Cavitation damages can best be understood by visualizing the sand blasting process.
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Now, imagine the air bubbles being the sand and hitting the metallic components of the hydraulic system. When a metal surface is sand blasted, the metal is chipped away giving it a rough or pitted surface. With that analogy, imagine the hydraulic system running continuously and what the air bubbles is doing to the systems internal components. These rules will control or eliminate cavitation of a pump by keeping the suction pressure above the vapor pressure of the fluid: 1) Suction velocity must be kept belo 5 ft / s (feet per second).
2) Keep pump inlet lines as short as possible. 3) Reduce the number of fittings in the pump inlet line to a minimal amount. 4) Mount the pump as close as possible to the reservoir (liquid storage container for the hydraulic system).
5) Use proper oil, as recommended by the pump manufacturer. 6) Keep the oil temperature from exceeding the recommended maximum temperature level. 7) Use a properly designed reservoir that will remove the entrained air from the fluid before it enters the pump inlet line.
8) Use low-pressure drop-pump inlet filters or strainers. Pump noise is created as the internal rotating components abruptly increase the fluid pressure from inlet to outlet. The abruptness of the pressure increases play a big role in the intensity of the pump noise. Therefore, the noise level at which a pump operates depends greatly on the design of the pump. When the pump begins to produce very loud noise levels, this usually means that cavitation has occurred. The noise level of the pump is not the only way to determine if the hydraulic system has encountered a cavitation problem.
Cavitation also causes a decrease in pump flow rate because the chambers do not completely fill with hydraulic fluid. As a result, system pressure becomes erratic or unsteady.
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“From the brain, and from the brain alone, arise our pleasure, joys, laughter, and jokes, as well as our sorrows, pains, griefs, and tears. Through it, in particular, we see, hear, and distinguish the ugly from the beautiful, the bad from the good, the pleasant from the unpleasant. ”(Attributed to Hippocrates, 5th century BCE, as quoted by Kandel et al. , 2000, as cited in Baars and Gage, 2012). ...
