To simulate the deep sea hydrothermal environment, a continuous micro-flow hydraulic system using seawater as working fluid is built with a flow range from 0.01 ml/min to 5ml/min, a pressure range from 0.1MPa to 60MPa and a temperature range from room temperature to 400°C. To precisely control the pressure of the continuous micro-flow seawater hydraulic system, a special nozzle-flapper proportional valve has been developed successfully. Moreover, a fuzzy self-tuning proportional-integral controller is proposed to accomplish the steady pressure control in the face of the severe parameter uncertainties and strong interference effects between pressure and different temperature or flow rate. Experimental results demonstrate that the developed proportional valve is competent to the pressure control of the continuous micro-flow seawater hydraulic system, and the fuzzy self-tuning mechanism ensures the robustness and effectiveness of the proposed controller for the nonlinearity in the system. The pressure value can be controlled within the desired range of ±0.1MPa.

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