Shaping the flow characteristics of a proportional directional valve

This article presents a methodology for designing control edges for proportional hydraulic directional valves for the use in hydraulic governor systems of hydro turbines requiring high flow rates. On the basis of multivariate CFD studies, the optimal shape of control edges was determined, ensuring the achievement of a proportional relationship between the increase in flow rate and the increase in opening of the spool located in the body of the directional valve. The results of the performed CFD tests for selected characteristic values of the opening of the spool of the directional valve at a certain pressure drop made it possible to create a mathematical description defining the flow rate through a proportional hydraulic directional valve. New mathematical formulas were proposed for calculating the liquid flow rate in the throttling gap of a proportional directional valve as a function of spool displacement and as a function of pressure drop across the gap. Based on the data obtained, a prototype proportional hydraulic directional valve was developed for high flow rates. Conducting laboratory tests of the directional valve confirmed the validity of the assumptions made for the development of throttle gaps in the spool of the proportional directional valve. A comparison of the flow rate characteristics as a function of spool displacement for a constant pressure drop for the values obtained during laboratory tests, CFD simulation tests and for the values obtained from mathematical calculations showed that the differences between the obtained values did not exceed 8% over the entire range of opening the throttle gap of the directional valve.