The analysis of the flow field inside hydraulic valves has become in the last few years a very important issue to be addressed in order to optimize the spool shapes and to obtain the desired flow metering characteristics. The Fluid-Power research unit of the Polytechnic of Bari realized many works dea領 with the Computational Fluid Dynamics (CFD) analysis of directional control valves. Experimental measurements concerning discharged flow rate and needed driving force values have been performed in order to validate the numerical results, but the validation of CFD results has been limited, in the past, only to the global fluid dynamic response of the valve and not to the local flow conditions. In order to provide the flow field inside the valve through PIV (Particle Image Velocimetry) measurements, a valve model, equipped with a great optical access, has been realized. The scaled model has been realized according to the fluid dynamic similarity laws in order to use a fluid different from the oil (water) and to increase the dimensions of the valve. In particular, the realized model has a circumferential development useful to acquire important data about the circumferential flows and their effects on the global flow rate crossing the valve. The experimental results show that the velocity profiles in the metering sections are strongly influenced by the three-dimensional effects of the flow, confirming the results obtained numerically in previous works. 德國LaVision PIV/PLIF粒子成像測速場儀 Imager SX PIV相機