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Air-driven hydraulic pumps are widely used to pump high-pressure oil for small hydraulic systems, where it is uneconomic to set up a conventional hydraulic power pack. To obtain good performance of a small hydraulic system, input air flow and output oil flow characteristics of the air-driven hydraulic pump should be properly understood. In this paper, based on a mathematical model which has been experimentally verified, the model of an air-driven hydraulic pump is proposed. Using the software MATLAB/Simulink for simulation, the dynamic characteristics of the pumps are obtained. To set a foundation for the optimization of the pump, the influence of key parameters on the output characteristics of the pump was studied. Through analysis, it can be obtained that, firstly, with an increase in the input air pressure, output oil pressure and area ratio, the ratio of output to input volume flow rate decrease approximately linearly. Moreover, when the output oil pressure was fixed, an energy-saving method to enhance the output oil flow is to enlarge the area ratio of the pump. Furthermore, the output oil flow can be increased rapidly through increasing the input air pressure, but that may result in an increase in compressed air consumption. This research is of use in the performance and design optimization of air-driven hydraulic pumps.Copyright © 2015 by ASME

Pressure reducing devices are the essential and critical components of a pneumatic system. But the energy lose due to the pressure reducing process is considerably huge when there is a high pressure difference. Aiming at this issue, firstly, the mechanism and quantification method of the energy loss in the throttling reducing process is analyzed based on pneumatic power theory. Then, a power recovery type (PRT) pressure reducer which can output shaft power during the reducing operation is proposed. The basic mechanical structure and the working principle of the PRT reducer are described. For evaluating the feasibility of the design, a thermodynamic model of the PRT reducer is established. And under specific parameter settings, simulations on the PRT reducer’s power output characteristics and the pressure regulating ability are carried out. On this basis, the principle structure of an energy recycling high pressure pneumatic system is proposed. This research is the theoretical foundation of the prototype design of a PRT high pressure reducing device.Copyright © 2014 by ASME

Air leakage is one of the most significant energy waste factors in compressed air systems which account for about 10% of total industrial energy consumption. It is estimated that about 10%∼40% of the compressed air is wasted through leakage in most plants. A new ultrasonic leak detection method based on time delay estimation (TDE) is proposed to locate the compressed air leak for preventing energy waste in pneumatic systems. The accuracy of detection is highly dependent on the performance of the TDE method. Performances of six typical TDE methods based on generalized cross correlation (GCC) are compared, and these methods are the basic cross correlation (BCC), the Roth impulse response, the phase transform (PHAT), the smoothed coherence transform (SCOT), the WEINER processor, and the Hannan-Thomson (HT) processor. The experimental results show that: Firstly, the accuracy and precision of time delay estimation increases with the observation interval for all these methods. Secondly, the success rates of Roth, PHAT, SCOT and HT are much higher than that of BCC and WEINER, among which the HT processor performs best with a highest success rates closely followed by the PHAT processor. Thirdly, the HT processor which is a maximum likelihood estimator gives the minimum standard deviation of the time delay estimate; however, the standard deviations of all these GCC methods are very small. The HT processor outperforms other GCC methods in terms of success rate and standard deviation. Consequently, it is preferable to apply the HT processor for this particular purpose.Copyright © 2012 by ASME