Measurements of the underlap for four-way valves gave results that the underlap was not only uneven but also geometrically asymmetric for some four-way valves. Both the unevenness and the asymmetricity have considerable influence on the characteristics of the valve-controlled cylinder.
In addition to the unevennesses i=(Δ₁/Δ)- 1, i= (Δ'₁/Δ')-1, the asymmetricity η=Δ'₁/Δ is introduced for a valve, where Δ, Δ' are the mean underlaps of the left side and the right side three-way valves and Δ₁, Δ'₁ are the underlaps on the supply sides. represents the right side.
Considering i, η and Δ of a valve, the frequency response of a valve-controlled cylinder with viscous friction, Coulomb friction and mass load was theoretically analyzed where the flow versus pressure characteristic curves were approximated partially as polynomials of degree 3 of the pressure.
The tendency shown by the theoretical results agreed fairly well with that of the experimental results. The frequency characteristics of (piston velocity)/(spool displacement) = V(jω)/ Y(jω)show the same tendency for an asymmetric valve as that for a symmetric valve. But, for the case where an asymmetric valve is used, there is null shift of the valve ( δο) for avoiding the piston drift. δο changes in proportion to i, and |δο| becomes larger according to the increase in η (for η>1) or 1/η (for η <1).δο changes little for the changes in Δ and frequency ω.

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Test results on the unsteady cavitation in long orifices are presented. Test was carried out under two flow conditions: (i) at constant Q. i. e., both the inlet pressure P₁ and the outlet pressure P₂ were changed stepwise but the flow rate Q was kept at a set value, and (ii) at constant P₁, Le., both Q and P₂ were changed stepwise but P₁ was kept at a set vabse.
From examination about the effects of oil temperature, pressure, orifice diameter, etc. on the cavitation delay time, it is found that unsteady cavitation is affected significantly by the degree of dissolution of gas nuclei to the orifice inlet. The time required for bubbles to grow to the minimum visible size by diffusion and/or by vapourisation is calculated, and it is shown that growth by vapourisation has an important role in cavitation of long orifices.

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