This paper deals with the modelling of sliding spool valves that are used in hydraulic actuation systems. A new model of continuity between opened and closed orifice configurations is proposed and validated from -40 to +32 degrees Celsius. It aims at reproducing accurately the experimental pressure gain, flow gain and leakage flow for a wide range of operating temperatures in the absence of detailed knowledge of the valve design. The proposed unified model of flow at valve orifices considers the mode of operation (opened or closed orifice) and the flow conditions (laminar or turbulent) with special attention to continuity around the hydraulic null. The leakage flow in closed orifice configuration is modelled with reference to a short orifice instead of a laminar gap between infinite planes. The parameter identification and model validation processes are presented in detail and the results are displayed for an aerospace flight control servovalve.

Keywords: flow gain, hydraulic, identification, low temperature characteristics, modelling, orifice, pressure gain, servovalve, spool valve