Abstract: This paper deals with the influences of the flow force and the viscous force on the final positions of a pilot
valve by means of the CFD method． It describes the high-frequency low-amplitude vibration of the valve in the range of the damper flow and discusses the key factors which cause the pilot valve to keep a steady position and a rapid dynamic response． For the relief valve，the geometrically-nonlinear partial differential equations of the annular plate under the concentrated，partially-distributed and globally-distributed loads are established． Then，it is pointed out that the distribution laws of the concentrated and partially distributed forces can be equivalently described by using the hyperbolic tangent function or the power function． Furthermore，the FEA method is used to analyze the dynamic behavior of the relief valve． Finally，according to relevant mathematic models，CFD results and FEA conclusions，an integrated model is constructed，and the calculated results are compared with the experimental ones． It is found that the
theoretical analysisis consistent with the experimental results and that the theoretical methods are feasible．

Key words: semi-active damper, pilot valve, relief valve, computational fluid dynamics, finite element analysis