A novel approach for predicting the operation of external gear pumps under cavitating conditions

This paper addresses the problem of predicting the effects of gas cavitation in fluid power components, accounting for the dynamic features of gas (including free air and vapour) release and adsorption. Several approaches to evaluate fluid properties under cavitating conditions have been proposed in the past, but those suitable to model hydraulic components with the classic lumped parameter approach do not consider the dynamic nature of the gas cavitation process. Cavitation can have a relevant impact on component operation, particularly for positive displacement machines directly connected to the oil reservoir. With the goal of studying the cavitation effects in hydrostatic units, in this paper a novel model to describe fluid properties - which utilizes a simplified formulation of the Full Cavitation Model - was integrated in an existing lumped parameter model for external gear machines previously developed by the authors' research team. While the basic formulation of the new fluid model was previously validated for a single closed fluid chamber, the present study extends its formulation for the case of complete systems in which multiple chambers with variable volume are connected to each other. A proper experimental set-up was developed to permit the validation of the proposed model for the case of external gear pumps. Comparisons between measured and simulated instantaneous internal tooth space pressures as well as the outlet flow rates are presented. The significance of the proposed model is highlighted by comparing its predictions with those obtained using classic models of fluid properties, which cannot predict with accuracy the effects of cavitation.