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.

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.

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.

This article deals with the experimental and numerical analysis of the leakage characteristics of the proportional directional valve. These characteristics describe the flow through the directional valve in the region of the center position of the spool valve. The element under investigation is a three-position four-way directional valve with zero overlap and feedback from the valve spool position. The actual valve spool position is sensed by an inductive position sensor and processed by integrated electronics. By means of an offset on the integrated electronics, it is also possible to set the center position of the valve spool. By moving the valve spool, the size and direction of the working fluid flow in both directions can be controlled. Internal leakage occurs due to axial and radial clearances between the spool and the sleeve. The magnitude of the axial clearances that occur at the control edges is investigated. The blocked-line pressure sensitivity curve, leakage flow curve and center flow curve are determined by experimental measurements. Depending on the experimental measurement, the correction of the center position of the valve spool is then made using offset. The flow through the control edges at the center position of the valve spool was simulated using Ansys Fluent software. Subsequently, the geometry of the flow simulation model is adjusted. The adjustment is made to take into account manufacturing tolerances. Finally, the simulated dependencies including the effect of manufacturing tolerances are compared with the measured and analytically determined characteristics.Research background: Spool valve description, mathematical equations, flow analysis through valve, radial and axial clearance.Purpose of the article: Effect of axial clearance on leakage characteristic.Methods: Experimental measurements, numerical simulation.Findings & Value added: Determining the range of the center flow curve as a function of manufacturing tolerances

This article deals with experimental measurement and numerical simulation of static and dynamic characteristics of the proportional directional valve. The characteristics of the proportional directional valve are measured on experimental equipment. At the static characteristic, pressure drop on the proportional directional valve, flow and oil temperature are measured on this equipment. The spool position is measured to determine of the dynamic characteristic of the proportional directional valve. Mathematical model of the proportional directional valve is created using Matlab SimScape Fluids software and is complemented by a mathematical model of the experimental equipment. The simulation results on the mathematical model are compared with the results of the experimental measurement.

Hydraulic hoses are part of most hydraulic systems, from industrial hydraulics with open loop hydraulic systems to mobile hydraulics with closed loop hydraulic systems. The design parameters of hydraulic hoses may influence the duty cycle dynamics of these systems. One of the factors that influence the behavior of a hydraulic hose under pressure loading is the steel braid angle with respect to the hydraulic hose axis. This work aims to determine the effect of the hydraulic hose braid angle on the change in its geometry. The next objective is to determine the forces that occur at the hose ends under pressure loading. The stresses occur when fluid pressure is applied to the inner wall of the hydraulic hose. Consequently, these stresses are transferred to the hose ends through the steel braid or spiral. The phenomenon of the neutral braid angle provides a balance between the stresses generated inside the hydraulic hose. Therefore, hydraulic hose manufacturers try to produce hydraulic hoses with a neutral braid angle, because the lifetime of the hydraulic hose is also related to this. As part of this research work, an experimental device was constructed in order to measuring the properties of hydraulic hoses. When the hose was loaded with fluid pressure, the change in hose geometry was measured and the angle of the hose braid was measured simultaneously. Upon the measurements, the effect of the braid angle on the hose behavior under pressure loading was determined.