Servo valves are critical components in hydraulic control systems; their performance directly affects the accuracy and reliability of systems used in aerospace and construction machinery. In service, micron-scale solid contaminants in hydraulic oil tend to deposit within the narrow clearances between spool and sleeve, causing spool sticking and accelerated wear that degrade system stability and lifetime. This study combines fluid–particle coupling analysis, numerical simulation, and experiments to examine particle motion and migration in representative valve-like flow fields. A force model for particles in viscous hydraulic oil is derived from fluid- and particle-dynamics principles, and two-dimensional CFD–DPM models are constructed for laminar, jet-like, and swirling flow conditions. Parametric simulations explore the influence of flow velocity, particle size, and particle density on particle trajectories and displacement. Results indicate that particle size has the strongest effect on migration behavior, with particle displacement increasing from 0.35% to 30.65% in laminar flow, from 2.31% to 67.08% in jet-like flow, and from 1.93% to 145.09% in swirling flow. Fluid velocity also significantly affects particle displacement, while particle density has a relatively minor influence. Swirling flow produces the largest displacement, followed by jet-like and laminar flow. Finally, a Particle Image Velocimetry (PIV)–style experimental platform on scaled models is used to validate key simulation trends. Findings clarify dominant mechanisms of particle contamination in servo valves and offer guidance for gap optimization and anti-contamination design.
Du et al. (2026) studied this question.