In the pipeline of a hydraulic system or a liquid transportation system, liquid column separation occurs when the pressure drops below the gas release pressure or saturated vapor pressure. When the cavity produced by the column separation collapses, an extraordinary high build-up of pressure, which is very harmful for the hydraulic system and the components, can occur. The behavior of the dissolved air contained in the liquid makes this even more complicated. To predict the duration of the separation and the peak pressure caused by the collapse, a simple one-dimensional model is proposed, in which gas-liquid surfaces are taken and the effect of released air is taken into account using a homogeneous mixture approximation and the method of characteristics. With regards to the first pressure peak, the calculated results agree well with the experimental ones.

抄録全体を表示

The effects of elastic deformation on the characteristics of hydrostatic bearings for hydraulic equipment are studied experimentally. The experimental apparatus consisted of test bearings (outer diameter : 60mm, ratio of a pocket diameter : 2/3), an elastic pad (outer diameter : 84mm), a restrictor (diameter : 2mm, length : 5mm) and six pistons for applying the loads. The experimental parameters were : the thickness of the elastic pads (thickness : 1, 2, 3mm and a rigid pad), the supply pressure (maximum pressure : 9.8MPa), the concentric and eccentric loads (maximum load : 12kN) and the speed of rotation (0 and 25 1/s). The leakage flow rate, frictional torque and displacement of the pad were measured. Furthermore, these results are compared with the theoretical results. The conclusions are as follows : 1) The deformation of an elastic pad causes a reduction in the load-carrying capacity and leakage flow rate. The effects become remarkable in the case of a thinner pad and high loads, 2) The gaps at the inner edge and at outer edge become smaller and larger by the deformation, respectively. Then, the frictional torque resulting from the metallic contact increases, 3) The eccentric loads let the flow rate increase; and 4) Regarding fluid film lubrication, the power loss is decreased by the deformation because the leakage loss is much larger than the frictional loss.

抄録全体を表示

Hydraulic systems often contain discontinuous nonlinearity due to collision with moving parts. In numerical simulations, the points of discontinuity are usually located between two adjacent mesh points of time. Inappropriate treatment to detect the location can cause noticeable errors. In this paper, the authors propose an interpolation method to precisely detect and locate discontinuity due to collision. In this method, the mesh size between the time interval including the discontinuity is subdivided so as to equalize the truncation error of detection of discontinuous points with that of the main calculation scheme. The effectiveness of the method is tested by a simple system having an exact solution and a poppet valve system. The results are shown to be satisfactory.

抄録全体を表示

An oil (water) hammer generates pressure exceeding that applied to a pipeline with consequent breakage on occasion. Many methods have been devised to prevent this. The authors propose actively using pressure rise by an oil hammer and a new hydraulic pressure intensifier. Applications of the intensifier to pressure control of a hydraulic cylinder have been reported.

The desired input signal for pressure control is time variable in the present paper. Output pressure follows input signal and generates a wave form whose value changes continuously. The maximum output pressure is several times that of the original pump pressure,1.98 MPa. Interactions between the check valve and oil hammer are considered in the simulation. A relatively high efficiency was confirmed to be possible by this intensifier.

抄録全体を表示