Orifices Flow Saturation in Oil Hydraulic Applications

Even though the orifice is the simplest and most common control component in fluid power systems and cavitation is an already well-established topic in the scientific literature, the flow choking or saturation effect is largely overlooked in the common engineering practice. Most of the times the phenomenon is completely ignored, unless the peculiar hissing noise is observed at the test rig, giving a hint that something wrong is happening in the hydraulic system. Even then, the focus is just on the possible component damage induced by strong cavitation, while the functional implications - in terms of flow characteristic - are neglected. The objective of the paper is to study the phenomenon of flow saturation in hydraulic orifices to assess the formulation of the different critical cavitation numbers and cavitation indexes available from literature. For this reason, a full factorial design of experiments (DOE) is performed to determine the influence of three factors: orifice size, fluid temperature and upstream pressure. The testing is carried out on 5 orifice sizes at 3 different temperatures and 5 different upstream pressure levels. In each test, the downstream pressure is changed from 0 to the upstream pressure level, to sweep the available ?p range, both ascending and descending. In the results section an analysis of the experimental results is drawn, proposing a correlation between the critical cavitation index and the factors considered in the DOE. To the authors' knowledge, no systematic analysis, as the one here proposed, currently exists in literature for mineral oil applications.