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In some circumstances, the hydraulic fluid can entrain some air from the environment that can lead to suction condition issues for the pump(s). This is commonly referred as pseudo‐cavitation.

This usually can occur in the reservoir (Figure 2.10a) or when gas leakages are present in low‐pressure hydraulic lines, such as suction lines (Figure 2.10b). For example, the return line entering the reservoir might present a non‐submerged pipe or a design creating a high amount of turbulence. In both cases the hydraulic fluid can entrap air that is then carried within the flow and can enter the hydraulic system. If the bubbles of air do not have enough time to settle within the reservoir, foam can accumulate on the surface.

The entrained air can lead to cavitation of the pump or to erratic phenomena such as a slow response of some functions. For this reason, it is always recommended to adopt all possible measures to avoid or limit the air entrainment.