The deep-sea environment has the characteristics of high pressure and low temperature. In addition to the extremely high requirements on the structural reliability, the ultra-high ambient pressure also has a great impact on the working characteristics of the hydraulic source. In this paper, the efficiency characteristics of a deep-sea hydraulic source are studied in the full-ocean-depth pressure range. According to the power transfer process, the efficiency of the deep-sea motor, gear pump and hydraulic circuit is analyzed. In so doing, the oil friction loss of the motor rotor, the internal leakage of the gear pump, the viscous friction loss of the hydraulic system, etc., are calculated. Then, simulating the deep-sea high-pressure environment by the pressure cylinder, the output characteristics and corresponding input power of the prototype are measured. By analyzing the experimental data, the efficiency characteristic curve of the hydraulic source prototype, changing with the ambient pressure, is obtained. The experimental and calculation results show that, with the increase of ambient pressure, the system efficiency of the hydraulic source prototype increases first and then decreases.

The measurement of the flow rate of various liquids and gases is critical in industrial automation. Rotary positive displacement meters (rotary PD meters) are highly accurate flowmeters that are widely employed in engineering applications, especially in custody transfer operations and hydraulic control systems. This paper presents a high pressure rotary PD meter containing a pair of internal cycloid rotors. It has the advantages of concise structure, low pressure loss, high accuracy and low noise. The curve of the internal rotor is designed as an equidistant curtate epicycloid curve with the external rotor curve as its conjugate. The calculation method used to determine the displacement of the cycloid rotor flowmeter is discussed. A prototype was fabricated, and experiments were performed to confirm measurements over a flow range of 1–100 L/min with relative errors of less than ±0.5%. The pressure loss through the flowmeter was about 3 bar at a flow rate of 100 L/min.