Hydraulic Cavitation and Aeration
Although aeration and cavitation are very similar, they are caused by completely different situations.
Cavitation occurs when air cavities are formed and are then collapsed in liquid. For example, when hydraulic fluid is being pumped from the reservoir, the suction line to the pump will drop pressure. The fluid then gets pushed into the pump, rather than sucked. Aeration is caused when there is a leak on a fitting. Fittings can become loose from years of vibration.
Most hydraulic oil contains around 9% of air that has been dissolved. When the oil is not flowing fast enough to the pump, air will be pulled out of the oil. The air then goes into the pump at a considerably high pressure, and then implodes. This can cause the pump to whine with a high pitched sound as damage is made.
It’s also possible for cavitation to occur when there are extreme temperatures. For example, bubbles can form when the fluid is at a high temperature but at low pressure. Again, bubbles that enter the pump can collapse and create cavitation. It’s also possible for low temperatures to make the oil more viscose, and this can prevent it from flowing into the pump. (Oils that have a high viscosity index will usually resist this tendency, but they can be expensive, and are therefore not widely used). A best practice is to not start a hydraulic system with oil that is colder than 40°F. Not until the oil has reached at least 70°F should the system be put under load.
If the right amount of fluid cannot be delivered to the pump due to the drive speed being too high, then that can also create cavitation. The pump should not be mounted above the hydraulic fluid level in the reservoir otherwise there will not be enough atmospheric pressure for the oil to be delivered to the pump inlet. This is something that is a tendency of systems that operate high above sea level, due to there being lower atmospheric level conditions.
Read our hydraulic system blog regularly for more information about how to avoid cavitation and aeration.