Radial flow force reduction in a hydraulic spool valve using balanced through-hole design

The hydraulic spool valve (HSV) represents the core control element in the fluid power system by virtue of its precise flow and pressure regulation abilities. Unbalanced radial flow force (RFF) is a major contributor to spool instability and friction-induced failure in HSVs, particularly in open-neutral configurations where flow field asymmetry is prominent. Conventional assumptions often overlook RFF due to structural symmetry, yet practical designs constrained by standard port layouts frequently induce asymmetrical pressure and velocity distributions. To address this issue, a novel through-hole design is proposed and integrated into the mid-shoulder of the HSV spool. Specifically, the study employs a combined approach of computational fluid dynamics-based numerical simulations and experimental bench testing to evaluate RFF generation and suppression mechanisms. The Realizable k–ε turbulence model is used to capture turbulent flow features and assess the contribution of pressure and viscous forces. Various through-hole angles are analyzed to determine the optimal configuration. Results indicate that RFF is predominantly pressure-driven (accounting for over 85% of total force), with significant asymmetries localized around the mid-shoulder region. Incorporating a 15° inclined dual through-hole structure reduces RFF on the mid-shoulder by 45.5% and total spool RFF by 29.9%, improving flow symmetry and minimizing pressure gradients. The optimized structure also enhances performance stability under varying spool displacements, achieving a maximum total spool RFF reduction of 55.5% at −1.5 mm displacement.