A pilot-operated solenoid valve is used to control ultra-high pressure vessels. However, it is difficult to understand its dynamic behavior because the valve operates under ultra-high pressure conditions and the driving unit moves in a multi-step fashion in a tight hidden space. This study aims to identify the system coefficient, especially the damping coefficient, required to analyze the dynamic behavior of a solenoid driving unit. Experiments to measure the dynamic behavior of the driving unit are conducted using two laser sensors and one accelerator. The damping coefficient is estimated using Matlab Simulink, by varying the damping coefficient to match the experimental results. The obtained system coefficients are modeled as equations of motion. It is verified that the valve motion consists of two sequential movements—Phase 1 by pilot plunger and Phase 2 by main plunger, pilot plunger, and the valve initiation time is as fast as 9.9 ms. The damping coefficient of each phase is estimated 0.001 N ∙ s/mm for Phase 1, 0.004 N ∙ s/mm for Phase 2.

Ultra-high-pressure hydrogen solenoid valves face a fundamental design challenge of operating across a wide pressure range from 2 MPa to 87.5 MPa. To address the conflicting requirements of effective sealing at low pressures and structural integrity at high pressures, this study proposes a novel concave contact geometry based on Hertzian contact theory. Finite element analysis examines the mechanical relationships between plunger curvature radius (R_ₚ), seat curvature radius (Rₛ), and eccentricity (e). Optimization utilizing Latin hypercube sampling and kriging metamodeling yields an optimal design (Rₚ = 5.73 mm, Rₛ = 4.68 mm, e = 0.95 mm) with an Rₚ/Rₛ ratio of 1.22. The optimized concave contact geometry achieves 23.7% higher contact pressure at 2.0 MPa and 42.7% lower maximum equivalent stress at 87.5 MPa compared to conventional rectangular geometry. Experimental validation confirms the concave contact geometry seals at 1.7 ± 0.2 MPa, below the AIS-195 standard requirement of 2.0 MPa and 69.6% lower than the rectangular design (5.6 ± 0.7 MPa). Structural analysis after 87.5 MPa high-pressure exposure reveals no measurable deformation in the concave design, while the rectangular design exhibits permanent deformation of 0.0580 ± 0.007 mm. This integrated methodology provides a framework for optimizing contact geometries in fluid control components operating under extreme pressure conditions, successfully reconciling contradictory requirements across the entire pressure range.