An experimental investigation of the flow inside a hydraulic valve by means of laser measurement technologies

In recent years, the analysis of the fluid dynamic phenomena inside the hydraulic valves has become very important in order to optimize the spool shapes and to obtain the desired flow metering characteristics. The Fluid-Power research unit from Polytechnics of Bari has realized many works dealing with the CFD (Computational Fluid Dynamics) analysis applied to the fluid dynamic behaviour inside directional control valves. Besides, experimental measurements have been performed in order to validate the numerical results, but the validation is limited only to the global values as the flow rate discharged by the metering section and the flow force acting on the spool. Obviously, more accurate measurement systems are needed to investigate the local flow conditions inside the valve. To this aim, laser anemometry systems (PIV: particle image velocimetry and LDA: Laser Doppler Anemometry ) have been purchased. A valve model, equipped with a great optical access has been realized. The scaled model has been created according to 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, this 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. In the past, these flows were studied by means of CFD codes. The experimental measurements will provide in the future a correct validation of the numerical results.