Mathematical modelling and simulation of a jet pipe electrohydraulic flow control servo valve

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In this paper, the mathematical model of a jet pipe electrohydraulic flow control servo valve with a built-in mechanical feedback is developed. The actuator dynamics is also included. The solid and finite element (FE) models of the critical and precision components, feedback spring assembly and flexure tube of jet pipe assembly, were carried out first and simulated with appropriate boundary and loading conditions in a commercially available FE code, IDEAS, version 7.0, to ascertain the stiffnesses. To validate the obtained finite element results, experiments were carried out with a specially designed and fabricated test set-up. Moderately good agreement was observed between finite element and experimental values. The required simulation parameters for a jet pipe servo valve-actuator system, such as the moment of inertia, mass of the spool, mass of the piston, stiffness of the critical and precision components, and lever arm length, were obtained from the solid and finite element models. The developed model was simulated in commercially available software, MATLAB 6.5, Release 13. The step response of the valve was analysed. The simulation clearly showed the dynamics of the jet pipe, spool, and actuator displacement in achieving the equilibrium position when the applied torque and restoring torques balance, known as the steady state.