Cavitation is a common phenomenon in many valves used in water hydraulic systems as well as in oil hydraulic systems. In this paper, the cavitation phenomenon in water hydraulic poppet valve is fundamentally investigated experimentally with a half cut test model. The cavitation appearance processes, the boundary of inception, the effects of cavitation on the characteristics of flow rate and pressure distributions are investigated. The results are discussed in comparison with the results of the similar tests with oil hydraulic valve in the former study.

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The characteristics of transient pipe flow influence the dynamic behavior of an oil hydraulic system. It is thus important to consider the transient flow in an oil hydraulic pipeline to determine the performance of the hydraulic system. In this paper, it is clarified that the calculation process for a transient pipeline system which, to date, has been performed using a computer program, is displayed wholly by one discrete-time block diagram. This block diagram consists only of time delay elements, proportion elements, and addition elements. A highly precise simulation result can be immediately obtained by drawing a block diagram on the display of a personal computer, using GUI (graphical user interface) simulation software. The pressure, flow velocity, and pressure loss are easily obtained at all points along a pipeline. Visual understanding of the calculation process is also facilitated.
Since the calculation process is displayed in the form of a block diagram using z transformation, the frequency response of the pipeline system, for which the characteristic method is used, is obtained by calculating the gain and phase of the discrete-time block diagram.

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The test method for the flow characteristics of a pneumatic solenoid valve is specified in ISO 6358. In this standard, the flow characteristics of a solenoid valve is shown by the sonic conductance and the critical pressure ratio, and these are calculated from the flow rate, pressure and temperature of the air that passes the solenoid valve. When the flow characteristics of a large solenoid valve are measured by this method, a large compressor and a large flow meter are required. Therefore the power consumption and the generating noise that arises during measurement become very large. In this study, a measuring method that can obtain the critical pressure ratio and the sonic conductance by using the small and low noise test equipment is developed. In this measuring method, at first the tank connecting to the solenoid valve that is to be measure for flow characteristics is evacuated and then the air is filled in the tank through the solenoid valve from the atmosphere. By using the pressure and temperature change in this tank, the sonic conductance and the critical pressure ratio of the solenoid valve are evaluated. In this report, this measuring method is named the charge method.

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A new simulation technique called the “system modal approximation” method for fluid transients in compound pipeline systems is developed and presented. Unlike existing approaches based on modal approximation of the input/ output causality of individual line elements, this new method is based on modal approximation of the frequency transfer function itself of the output (wanted variable) to the input (source), considering the total system dynamics This simulation technique also has these features only the numerical data of the frequency response of transfer matrix parameters of individual line element, which may be given from either theoretical model or experimental measurements, is needed, and the desired output variable alone can be calculated selectively in the time domain by a simple algebraic expression in the form of a recurrence formula For complex pipeline systems the superiority of this technique to other existing modal approximation-based methods in accuracy, easy applicability, flexibility, computation time, etc. is discussed with experimental comparisons.

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