Air entrainment in hydraulic systems

Researchers from Opus Systems and Hosei University designed a device to remove bubbles or foam in working oils for improved performance.

A trend in industrial manufacturing is for fluid-power systems, as well as fluid-power components, to be designed more compactly. The benefits of smaller fluid-power systems are obvious and include economy of materials, less energy consumption, and less required space. One often-overlooked drawback is the increased probability of air entrainment for fluid-power systems that incorporate smaller reservoirs. Another recent trend in fluid-power systems is biodegradable oils from vegetables for environmental compatibility of systems in Europe, North America, and Asia. But working fluids derived from the vegetable oil are unstable at high temperature and degrade quickly, and some manufacturers for biodegradable oils strongly recommend using these products only below 350 K.

Bubbles or foam in working oils influence the performance of fluid-power systems and may cause problems such as acceleration of oil degradation by oxidation, decreasing lubricity caused by air emulsion, reduction of thermal conductivity, cavitation erosion, higher noise emissions, an increase in compressibility and decrease in dynamic characteristics, and decrease in pump-output efficiency. When bubbles in oil are compressed adiabatically at high pressure, the temperature of the bubbles rises sharply, and the surrounding fluid temperature also rises. Thus, it is important to eliminate the bubbles from the oil to preserve oil quality, system performance, and to avoid possible damage of the components.