Water hydraulic fluid switching transmission (FST) has lower environmental load and lower energy loss in a valve for using only ON/OFF valves. In addition, FST can recover kinetic energy during the deceleration phase. This paper is concerned with experimental results of the FST system. First, it was shown from experimental results that the error rate during the constant phase was limited to 5 percent. Next, two performance indices were introduced to analyze the energy efficiency of water hydraulic FST. Then, it was shown that the recovered energy during the deceleration phase was more than 30 percent of the kinetic energy of a flywheel. Therefore, the validity of water hydraulic FST was confirmed.

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This paper describes a new approach to improve the performance of a hydraulic servo system using high bulk modulus oil. First, the property of the high bulk modulus oil is explained. Then the relationship of the performance of a hydraulic servo system and high bulk modulus is theoretically explained. Finally, the performance of a hydraulic servo system using high bulk modulus oil is investigated under the conditions of open loop pressure control. From the basic experimental results, the advantage of high bulk modulus oil over the mineral oil is verified.

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Steady and unsteady pressure losses in sudden expansion and sudden contraction in pneumatic piping systems are studied. An experimental study for steady state loss coefficients was carried out with pipes having expansion ratios (=pipe diameter ratio) of 1.2, 1.5 and 2.0, and contraction ratios of 5/6, 2/3 and 1/2. The Reynolds number downstream of the sudden cross section changes lies between about 5,000 and 36,000. The difference between the obtained loss coefficient and commonly known data that were obtained with water is about 10%. After steady-state measurement, pressure losses due to the cross-section changes in pulsatile flow are estimated and compared with the experiments. The estimate was made ignoring the compressibility of the fluid, and assuming the same value of loss coefficient as in the steady flow. The experiments were carried out using the same expansion and contraction pipes used in the steady-state experiment. The frequency of the pulsation is 1∼30[Hz]. The mean Reynolds numbers of the pulsatile flows were 12,000∼26,000 and the amplitude Reynolds numbers were about 27% of the corresponding mean Reynolds numbers. Differences between the estimates and the experiments are within 3% with contraction pipes, up to 15% with expansion pipes.

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