For the purpose of studying the steady flow field of an impact modulator, the coaxial impingement of two opposed plane turbulent jets is considered. Since it is impossible to obtain an analytical solution, a direct numerical solution of the elliptic equations, governing the steady turbulent flow of the impinging jets, in finite difference form is proposed under acceptable simplified conditions. As a mathematical model of turbulence, the semi-empirical differential turbulent-viscosity model, proposed by Prandtl and extended by Emmons, Spalding and Wolfshtein to two-dimensional flows, is applied. To insure convergence at high Reynolds numbers, the up-wind differences are adopted for the calculation of vorticity and turbulence energy. For iterative calculations, a point successive substitution method is used.
Convergent solutions are obtained for a wide range of nozzle Reynolds numbers, and show reasonable agreement with experiments.

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This paper deals with the attenuation characteristics of expansion chamber-type hydraulic pulsation absorbers, especially taking into consideration the pulsation of the delivery flow of pumps.
In carrying out experiments, a rotary spool-type hydraulic vibration machine capable of producing a sinusoidal pulsating flow of large amplitude up to about 800 Hz was recently developed, which enables accurate experiments covering a wide frequency range from the 1st to the 3rd pulsation components of common pumps.
After dividing the components of the absorber into circular pipe elements, the transfer matrix method is used to predict the attenuation characteristics.
The following results were obtained:
(1) The calculated values, obtained by applying the wave equation of two-dimensional viscous flow to all divided circular pipe elements and inlet and outlet conduits, agree well with the experimental values, except for some in the frequency range for which mechanical vibration cannot be disregarded.
(2) It is possible to treat fluid motion in an absorber as a lumped parameter system, since the lengths of the expansion chamber and connecting conduit in the absorber are, in general, fairly short compared with the corresponding wave length of the pulsation frequency of the pump.
(3) The approximate equation, which represents effects of the inlet conduit, the outlet conduit and the absorber independeals, . is accurate enough for practical use in the case of high loads.

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The performance of poppet valves commonly used in oil hydraulic equipment is affected by cavitation. Although it is essential to understand these effects, very little is known about them.
In order to clarify the cavitation characteristics of poppet valves, the cavitation tests were carried out on 15 kinds of poppet valves which are obtained by changing the combination of valve face angle 2a and valve seat width S. Briefly, the results obtained are as follows:
(1) With the exception of S=0. The flow rate of the cavitating flow is constant independent of the pressure drop ΔP across the valve, but depends on the pressure P₁ upstream from the valve.
(2) In this test a hysteresis effect is observed and it is only noticeable for valves with larger S and 2α.
(3) The flow coefficient C for various back pressures P₂ is affected by S and the sectional area A(H) of the annular passage way of the valve, regardless of whether cavitation occurs or not. (4) The pressure P₁ is linearly proportional to the critical back pressure P_ic and their gradients are different depending on S, 2α and A(H). (5) The coefficient Kc indicates that the critical vanishing point of cavitation is greatly affected by the value of S and 2α. Where Kc is the ratio of P_ic (absolute) to P₁, (absolute).

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