Influence of the Spool Velocity on The Performance of a Directional Hydraulic Valve

In this paper an accurate numerical method has been used to verify the influence of the spool velocity on the performance of a directional hydraulic valve (4/3, closed center): the flow during the opening phase of the valve has been solved by Direct Numerical Simulation (DNS), using an Immersed-Boundary (IB) technique. The present results have been compared with the ones of a previous study, based on the same numerical method, but with a stationary spool. The numerical comparisons prove that the "quasi-stationary" hypothesis is approximately correct for present commercial devices, but it is not suitable for future high-speed valves. However it is shown that, even inside the range of the spool velocities currently adopted, for small pressure drops Δp and small openings s more significant differences arise on the axial forces.