Evaluating the Influence of Leaking Active Check Valves in Digital Displacement® Units

This paper presents a framework to evaluate different power losses in regards to hydraulic valves used in Digital Displacement ® Units (DDU). The feasibility of DDU may be compromised if internal leakage in the hydraulic valves develops over time, introduction of a time-dimension is the objective of this work. The actual leakage that will develop over time due to mechanical wear is unknown, which is the main reason why previous work has not addressed this research topic. The underlying assumption of the developed framework is that internal leakage propagates as a consequence of the amount of valve switching cycles. This assumption is combined with physical knowledge about a DDU into one theoretical framework, which is defined both as non-linear differential equations and as a timeaveraged static model to visualize the difference in accuracy when put into context of a specific machine. Thereby reducing the required simulation time and enhancing design possibilities. The main contribution of this work is a revision of the conventional efficiency curve of a DDU, where it now includes a novel trade-off between averaged displacement and efficiency (without partial strokes). Over a period of 25 years an average displacement of 55%. is shown to be optimal from an energy perspective.