【正文】 cavitation, and (b) cavitation incipience and finale varied with the initial condition, the temperature of hydraulic oil, and the rate of pressure drop. Johnston et al. [9] carried out an experimental investigation of flow and force characteristics of hydraulic poppet and disc valves using water as the working fluid. The axisymmetric valve housing was constructed from clear perspex to facilitate flow visualization。 tests were performed on a range of different poppet and disc valves operating under steady and noncavitating conditions, for Reynolds numbers greater than 2500. Measured flow coefficients and force characteristics showed obvious differences depending on valve geometry and opening. Vaughan et al. [10] conducted putational fluid dynamics (CFD) analysis on flow through poppet valves. Simulations were pared with experimental measurements and visualized flow patterns. A qualitative agreement between simulated and visualized flow patterns was identified. However, errors in the prediction of jet separation and reattachment resulted in quantitative inaccuracies. These errors were due to the limitations of the upwind differencing scheme employed and the representation of turbulence by the k – 1 model, which was known to be inaccurate when applied to recirculating flow. Ueno et al. [11] investigated experimentally and numerically the oil flow in a pressure control valve under an assumption of noncavitating conditions for various configurations of the valves on the basics of a finite difference method. They concluded that the main noise of the testing valves was generated from cavitation, and the noise was affected by the valve configuration. Pressure measurements and flow visualization at two locations in a valve chamber were also performed on the basis of twodimensional models. Through parisons of the measured and calculated results, several design criteria were set up for lownoise valves. Martin et al. [12] investigated cavitation in spool valves in order to identify damage mechanisms of the related ponents. Tests were conducted in a representative metal spool valve as well as a model being three times larger. Data taken under noncavitating conditions with both of these valves showed that the orientation of highvelocity angular jets would be shifted due to variations in valve opening and Reynolds number. By means of highfrequency response pressure transducers strategically placed in the valve chamber, the cavitation could be sensed through the correlation of noise with a cavitation index. The onset of cavitation could be detected by paring energy spectra for a fixed valve opening with a constant discharge. The incipient cavitation index, as defined in this investigation, was correlated with the Reynolds number for both valves. Gao et al. [13] performed a simulation of cavitating flows in hydraulic poppet valves by means of an renormalization group (RNG) k –1 turbulence model, which was derived from the nstantaneous Navier–Stokes equations based on the RNG theory. Experiments were conducted to catch cavitation images around the seat of a poppet valve from perpendicular directions, using a pair of industrial fibre scopes and a highspeed visualization system. The binary cavitating flowfield distributions obtained through digital processing of the original cavitation image showed satisfactory agreement with numerical results。 the vibrations of valve body and poppet induced by the cavitating flow were detected using a vortex displacement transducer, a laser displacement metre and a digital strain device. It was concluded that the opening and cone of a conical valve had significant effects on the intensity of cavitation. However, in this study, only downstream cavitation inception volume was analysed in estimating the anticavitation capability, whereas the effects of outlet pressure were not considered. Oshima et al. [14] experimentally investigated the influences of (a) chamfer length in the valve seat, (b) the poppet angle, and (c) the oil temperature on the flow characteristics and the cavitation phenomena, using water instead of oil as the working medium in water poppet throttles. The cavitation phenomena were directly observed and the pressure distribution between the valve seat and poppet surface was measured in water poppet throttles. Comparison analyses on the condition of critical cavitation were conducted between oil and water. It was found that the discharge coefficient and the critical cavitation number for water poppet throttles were considerably different from those of oil ones, due to the high density and low viscosity of water. Recently, Liu et al. [15, 16] investigated experimentally the flow and cavitation characteristics of a twostage throttle in water hydraulic system。 they concluded that the twostage throttle had stronger anticavitation capability than the singlestage one, and that the shape of seats also affecte