Magnetorheological finishing of hydraulic spool valves for leakage control and performance improvement

Hydraulic spool valves operate under micrometer-scale clearances, where surface integrity directly governs leakage, friction, and system efficiency. Conventional finishing methods such as grinding, honing, and lapping are often insufficient to achieve the ultra-smooth surfaces required for high-performance applications. In this study, magnetorheological (MR) finishing was applied as a deterministic surface engineering technique using a magnetically controlled flexible abrasive interface for uniform, damage-free material removal. The process reduced surface roughness from 0.32 µm to 0.020 µm (∼93% improvement) and increased microhardness by ∼4.22%, indicating enhanced load-bearing capacity. These surface modifications resulted in a reduction in leakage from 1.8 ml/min to 1.15 ml/min at 200 bar (∼36% improvement), along with a 31% decrease in wear depth after 50,000 cycles. The combined reduction in leakage and friction contributed to an estimated 8%–12% improvement in system-level energy efficiency. Overall, the results demonstrate that MR finishing not only refines surface topography but also significantly enhances sealing performance, durability, and functional reliability, establ