Development of Low-Noise Piston Pump-Motor Unit for Raw Water

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As power transmissions for relative large power levels, oil-hydraulic drives have been widely adopted due to their superior controllability. However, mineral oils are used as working fluids, then, the hazard of fire, dangerous working environment and used oil disposal are of great concern.The aim of the study is, by using a raw water (tap water) as a working fluid, to solve these problems without damaging the feature of fluid drives, that is, to develop raw-water-hydraulic systems, which are a human-friendly and environment-adaptive system. A raw water is low viscous and corrosive, then, the problem of utmost importance is to develop a pump-motor unit.Therefore, in this study, we decided to develop a piston type pump-motor unit of maximum pressure 14 MPa, displacement 15 ml/rev and rotational speed 3000 rpm. To use the fund reasonably, we tried at first to realize a fluid film lubrication on sliding parts of a pump on the market so as to be suitable for a raw water and low speed charac … More teristics under motor operation.For the sliding part between a valve plate and cylinder block, we have solved the equations of motion to determine the film shape, and obtained satisfactory results on the valve plate dimensions with hydrostatic pads. Moreover, we have obtained the piston dimensions so as to minimize the power loss between the piston and bore. As a restrictor for the hydrostatic pads, an orifice type is finally selected, because the manufacturing process is less difficult than that of a capillary type.The trial production designed by the above mentioned process was tested under the conditions ; delivery pressure 14 MPa and rotational speed 1500 rpm. The maximum efficiency was 81% and the corresponding volumetric and mechanical efficiencies were 92% and 88% respectively. These values are lower than the expected. This is mainly due to the insufficient accuracy of the orifice restrictors.Therefore, it is necessary that the improvement of manufacturing accuracy of the restrictors for case of non-metallic materials and development of hydrostatic bearings with wide tolerance limits in the restrictor dimensions. Less