This paper deals with the analysis of leakage characteristics of the proportional directional valve. These characteristics distinguish a real directional valve from an ideal one. The ideal directional valve is characterized by zero leakage due to its perfect geometry. The investigated element is the three-position four-way proportional directional valve with zero spool lap and feedback from the spool position. The spool position is measured by the inductive position sensor and processed by external electronics. Internal leakage occurs due to axial and radial clearances between the spool and the sleeve. The magnitude of axial clearances that occur at throttle edges and their effect on the directional valve leakage is the subject of research. The blocked-line pressure sensitivity curve, the leakage flow curve and the center flow curve are determined by experiment. Individual characteristics are determined for different working fluid temperatures and different supply pressures. The flow through internal leaks in the center position of the valve spool is determined by analytical calculations. The flow through internal leaks is also simulated using the Ansys Fluent software. Subsequently, the geometry of the flow simulation model is modified to take into account manufacturing tolerances. From simulation results, the effect of the manufacturing tolerance magnitude on the internal leakage of the directional valve is evaluated. Finally, simulated dependencies are compared with experimentally determined characteristics.

This paper deals with the experimental and numerical analysis of the flow force acting on the spool of a proportional directional valve. The flow force arises due to the fluid flow through the flow path of the proportional directional valve and significantly influences the dynamics of the valve spool. The valve under investigation is a three-position four-way proportional directional valve with zero spool lap and feedback from the spool position. The dependence of the valve spool flow force on the volumetric flow rate is measured as part of the experiment. The measurements are performed for different spool displacements. The measured data will be used to verify the numerical simulations. The proportional directional valve was modified so that a force sensor could be included on the spool axis to realize the experiment. Firstly, the flow force is measured as the fluid passes through the two flow paths of the valve (PB and AT). Subsequently, the experimental setup is modified to determine the flow force when the fluid passes through each flow path separately. The measurements are compared. Simulations of the flow through the proportional directional valve are performed using Ansys Fluent 2022 R2 software to determine the flow forces acting on the valve spool. Simulations are performed for the selected spool positions of the proportional directional valve. Finally, the results of the simulation and the experiment are compared. The contribution of this study is a CFD model of the flow paths of the proportional directional valve verified by experiment. The CFD model will allow the flow force analysis for different flow path geometries of the investigated valve. Experimental analysis of flow force is performed over the entire spool stroke at different volumetric flow rates. The flow forces are measured for each flow path separately and for both flow paths simultaneously.

In today’s unmanned productions systems, it is very important that the manufacturing processes are carried out efficiently and smoothly. Therefore, controlling chip formation becomes an essential issue to be dealt with. It can be said that the material removal from a workpiece using machining is based on the degradation of material cohesion made in a controlled manner. The aim of the study was to understand the chip formation mechanisms that can, during uncontrolled processes, result in the formation and propagation of microcracks on the machined surface and, as such, cause failure of a component during its operation. This article addresses some aspects of chip formation in the orthogonal and oblique slow-rate machining of EN 16MnCr5 steel. In order to avoid chip root deformation and its thermal influence on sample acquisition, that could cause the changes in the microstructure of material, a new reliable method for sample acquisition has been developed in this research. The results of the experiments have been statistically processed. The obtained dependencies have uncovered how the cutting tool geometry and cutting conditions influence a chip shape, temperature in cutting area, or microhardness according to Vickers in the area of shear angle.

The article focuses on the experimental determination of the amount of released gas due to cavitation using an optical evaluation method. Cavitation is induced by the mineral oil flow through a throttle valve which characterizes commonly used valves in oil hydraulic systems. Cavitation zones are influenced by the defined experimental conditions. The influence of flow velocity, downstream pressure, and valve displacement on the development of gas phase due to cavitation is evaluated. Depending on the defined experimental conditions and the throttle valve displacement, a specific amount of released gas phase is monitored in the assembled observation window. The results give an overview of the amount of gas phase in the form of the bubble size distributions, volume and mass fractions that are released from the mineral oil when cavitation occurs under the defined experimental conditions. With respect to empirically acquired data, it can be said that the volume and mass fraction evolution of released gas phase, depending on the cavitation number, can be suitably described by a power law with an appropriate order of scaling. At the same time, a change in the determined curves during the initial phase of cavitation is found. Based on measured data, it can also be said that depending on the experimental conditions, up to 1 vol. % of air is present in the assembled observation window. It is also determined that up to 8% of air is released from the dissolved state depending on the achieved experimental conditions.

The aim of the paper is to evaluate hydraulic systems in terms of energy and dynamic properties. There are flow and pressure losses that have influence on total efficiency of hydraulic systems. The systems are compared from lower...

Rad se bavi mjerenjem i matematičkom simulacijom širenja hidrauličnog crijeva, uključujući učinak modula stlačivosti ulja. Youngov modul elastičnosti hidrauličnog crijeva eksperimentalno je određen metodom ekspanzije i metodom...