Influence of Notch Shape and Number of Notches on the Metering Characteristics of Hydraulic Spool Valves

The paper presents theoretical and experimental results of studies on the influence of shape and number of spool notches on the discharge characteristics (discharge coefficient, velocity coefficient and flow angle) of a hydraulic distributor metering edge. The flow-rate vs. pressure drop and the steady state axial flow-force vs. pressure drop diagrams are determined for spools with different configurations of multiple notched metering edges. Various combinations of the shape and number of the notches modulating the metering area of the passage between supply and drain ports were investigated and correlated with flow-rate, axial flow-force and pressure drop, in order to get estimates of discharge coefficient and flow angle. The procedure is applied to all the data collected during the experimental activity, and shows the behaviour of the flow characteristics in both the fully turbulent and transitional region of motion. The influence of notch shape and number on the metering edge flow characteristics is evaluated as well