Cavitation erosion produced by impingement of a cavitating jet was experimentally studied using aluminum alloy specimens in tap water. The effects of nozzle holder and configuration of the impingement surface on mass loss were investigated. Furthermore, numerical simulations of two-dimensional jets were conducted to clarify the effects of the nozzle holder, i.e., the configuration around the nozzle outlet.
Main points of interest are as follows :
(1) The erosivity of the cavitating jet is enhanced significantly by the restrictive wall around the nozzle outlet. The numerical simulation of the two-dimensional jet shows that the restrictive walls on both sides of the nozzle outlet lower the pressure near the nozzle outlet, changing its flow structure. For that reason, the restrictive wall favors cavitation to occur.
(2) The erosivity of the cavitating jet is also affected significantly by the configuration of the impingement surface.

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Microcomputers are being widely used in various fields including the controls of some hydraulic systems, and their applications to other hydraulic and pneumatic systems are being widely studied now.
As one of such studies, the dynamic characteristics of the system in which four hydraulic cylinders were connected to each other in series and all were controlled by a microcomputer have been investigated by experiments using a model system in this research. Especially, the case has been investigated when the stroke of each cylinder (unit; cm) varies in a sequence of two powered integers starting from zero. The total displacements, as the output of the system, can be any integer in the unit between zero and the square of the number of the cylinders using a proper combination of all the strokes. The ON/ OFF actions of each cylinder were controlled remotely and hydraulically by solenoid valves which were activated by the binary signals from the microcomputer.
Such systems have no feedback controls and no electric devices around the actuators, so that the systems have extremely high reliability and repeatability even in the hazardous fields such as in explosive gases or in strong magnetic fields.
This paper reports on the following results obtained from the research on such systems. That is, the positioning by such systems is reliable enough, but the position paths as the output of the system are not smooth in some certain cases. The paths can be made much smoother if the switching timings of directional control valves are adjusted suitably by a microcomputer.

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In the first report, the operating moment, the trunnion supporting forces and cylinder pressure of a swash plate type variable delivery axial piston pump were investigated experimentally in the quasi-zero swash plate angle region, and a model of the swash plate zero angle restoring moment was proposed. Furthermore, supplementary experiments were performed to test the model.
In this report, basic equations were derived based on the above-mentioned model, and a new calculation method was proposed to predict the operating moment and swash plate angle relative to the cylinder block of the pump, in the quasi-zero swash plate angle region. The calculated values showed good coincidence with the experimental results and the accuracy of the mathematical model was ascertained.
Furthermore, methods to improve the pump characteristics in the quasi-zero swash plate angle region were investigated using the prediction method, and a fundamental concept for improvement was proposed.

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