Study of flow characteristics in an unloaded spool valve with positive overlap and annular slit near the neutral zone

Abstract

This paper addresses the significant challenge of uncertainty in the flow characteristics of servo valves near the neutral zone. We present an innovative flow modeling approach that incorporates the structural parameters of the spool valve to effectively tackle this issue. A novel transition function calculation method was developed to accurately model the flow dynamics between the annular slit and orifice flow during spool movement. The design boundaries for the transition function were established based on three times the positive overlap of the spool valve pairs, a critical factor in our analysis. We also designed a method for obtaining time-varying flow coefficients, enhancing the model's responsiveness to operational changes. Our findings indicate that when the spool is positioned near the neutral zone, the fluid flow state transitions into a mixed flow regime, rather than remaining strictly laminar or turbulent. Additionally, we explored the impacts of pressure differential, positive overlap, and annular slit size on model accuracy. Results demonstrated that excessively small positive overlaps and large annular slits negatively affect the model's precision, while pressure differential has negligible influence. Experimental validation confirmed the accuracy of our developed model, offering valuable insights for more precise nonlinear modeling in valve-controlled systems.