Water hydraulic systems face challenges in precise flow control due to the low viscosity of water-based liquids. High-speed on/off valves offer a solution by providing discrete flow outputs for water-based liquids continuous flow control. This paper presents a novel approach to proportional flow control in these valves, focusing on estimating and controlling spool position using only current feedback. The proposed method integrates a robust controller with a high-gain extended state observer (HGESO). The HGESO estimates spool position and unmodeled disturbances based on coil current, deriving the system's output flow. The robust controller then adjusts the spool position to control the overall flow. Simulation and experimental results demonstrate the controller's ability to track desired flow rates under various conditions. This research contributes to water hydraulic systems by offering an effective method for position tracking control without direct position sensors. The study provides a valuable solution for improving the performance and precision of hydraulic systems in various applications. By addressing the challenges of water-based hydraulic systems and offering a practical approach to flow control, this research has significant implications for advancing the field of hydraulic control systems.