In a hydraulic circuit with a conventional flow control valve a deceleration valve is often used to avoid shock motion during speed change of an actuator which damages driven tools or work pieces.
In this study, a new-type flow control valve mechanism was utilized to eliminate such shock motion without using a deceleration valve. This valve is an improved version of a non-jumping flow control valve which was reported to be much better than the conventional one by the present authors. Experimental results with a sample valve revealed smoother motion of the hydraulic cylinder and far less surge pressure in the circuit than those of the non-jumping valves. These good characteristics are analytically explained and the design method is presented.

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Cylindrical short chokes are used many times in hydraulic valves to prevent or dampen the selfexcited vibrations. The frequency characteristics of the choke, especially for the case where the valve spool is vibrated at amplitude under 0.1 or 0.2 mm and frequency over 100 Hz, are experimentally and theoretically studied. The results obtained are as follows:
(1) The theoretical equation obtained by the addition of two components to Poiseuille's Equation, the additional component due to the energy loss near the entrance of the choke and the inertial component of oil, gives good agreements with experimental results.
(2) In case of high frequency, even though the volume is small, the compressibility of oil between the spool and choke has a significant influence.
(3) The influence of compressibility becomes more significant with larger spool amplitude, lesser choke diameter, lower oil temperature and higher frequency.
(4) The effects of various factors were made clear by investigating the percentage and influence of viscosity, additional and inertial components of the choke's equation.

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