The spring-driven ball-type check valve is one of the most important components of hydraulic systems: it controls the position of the ball and prevents backward flow. To simplify the structure, the spring must be eliminated, and to accomplish this, the flow pattern and the behavior of the check ball in the L-shaped pipe must be determined. In this paper, we present a full-scale model of a check ball made of acrylic resin, and we determine the relationship between the initial position of the ball, the diameter of the inflow port, and the kinematic viscosity of oil. When kinematic viscosity is high, the check-flow rate increases in a standard center inflow model, and it is possible to greatly decrease the check-flow rate by shifting the inflow from the center.

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The paper considers a stack of modular Load Sensing closed centre proportional directional control valves of a commercial excavator. All modules in the stack were disassembled and 3D models were prepared with the perspective of developing an accurate AMESim model. Previously, specific field measurements were also performed on the vehicle to set proper ground for subsequent validation of the simulation model. However, in the course of these in-depth investigations on all modules, some distinctive and rather peculiar aspects emerged. More precisely the pressure compensator featuring two independent spools, though located upstream of the main spool, is “normally” closed and in evident contrast with traditional pre-compensated solutions. In addition, the “global” Load Sensing signal driving the variable displacement pump differential pressure limiter is not originated by the highest load via proper selection in cascaded shuttle valves. The signal is rather generated by one of the two compensator spools through axial notches fed by a modest control flow directly derived from the pump delivery line. It is on this ground that, arbitrarily, due to their mixed origin, the term “hybrid” has been used in relation with these proportional directional control valves. The paper will detail all these findings and will further elucidate the AMESim model of one such modules. Finally simulated and experimental results will be contrasted to provide adequate support to the proposed modelling approach and a thorough analysis on specific parameters will be discussed.

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