This paper studies influence of the magnitude of charging-pressure-step and the pressure measuring time to the error of leak detection by the pressure charging method. In this method, compressed air is charged into a vessel whose leak should be examined. A leak changes the pressure in the vessel after the charging. However, the heat transfer around the vessel also changes the pressure. When the charging pressure is low, the temperature rise due to the compression is low; hence the thermal effect is small by low charge pressures. The experimental results in this study indicate that tests with higher pressures induce greater difficulty in leak detection. They also show that a longer duration of the pressure measurement decreases the error of the leak detect.

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Air bubbles in hydraulic oil lower the efficiency of hydraulic systems and contribute to instrument malfunctions. To mitigate these problems, it is possible to use an active “bubble eliminator” that uses swirl flow to remove air bubbles. This study aims to optimize the shape parameters of the device. For this purpose, its performance needs to be evaluated precisely. To evaluate the performance of the bubble eliminator, we should consider a correlation between the effect of swirl flow and axial flow because these flows affect the bubble behavior in the device greatly. In this paper, we perform the experimental flow visualization and numerical simulation with different values of the diameter of the outlet and vent port. Additionally, this paper presents a new performance index named “spiral number” and evaluates the performance of the bubble eliminator using this index. This index considers the correlation between the effect of the swirl flow and axial flow. We analyze the experimental and numerical results using this index, and show that the index is useful for evaluating the performance of the bubble eliminator. We conclude that the diameter of the outlet port and vent port can be selected using this index.

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