Which term describes the presence of dispersed bubbles of air in hydraulic fluid?

Which term describes the presence of dispersed bubbles of air in hydraulic fluid?

• A. Accumulator
• B. Cavitation
• C. Aeration (correct)
• D. Filters

Answer: (C)

Air in hydraulic fluid shows up as aeration, where tiny bubbles are dispersed throughout the oil. This occurs when air enters or is released from the fluid during operation, filling the hydraulic space with compressible pockets. Because the fluid isn’t purely incompressible anymore, the system’s response becomes spongier and less precise—the pressure response is damped, valves can feel sluggish, and pumps may run noisier or overheat as energy isn’t transmitted as cleanly. This is different from cavitation, which involves vapor cavities forming from local low pressure and can damage components, and different from an accumulator (a device for storing energy using a gas chamber) or filters (which remove solids). So aeration is the right term for dispersed air bubbles in the hydraulic oil.