A Mechanism for Self Excitation in Hydraulic Control Devices

Abstract

<p>Researchers in recent years have attributed the dynamic instability of certain hydraulic control devices (such as gates, valves, and seals) to a velocity dependent hydrodynamic load which is equivalent to a negative damping coefficient in the differential equation of motion. Such a model is not capable of predicting certain important features of observed check valve behaviour.</p> <p>A semi-empirical model for check valve self-excited vibrations is derived. The results show that the gross behaviour of this model is qualitatively the same as the experimental observations. Hence, the existence of a hydrodynamic load component in phase with displacement appears essential for the hydrodynamic load modelling.</p> <p>A general mathematical model is then derived from first principles. Closure of the hydraulic control device during vibrations and unsteady flow phenomenon including viscous losses are taken into account. The proposed model can be applied to any type of hydraulic control device with a jet-flow mechanism of excitation. Two applications for the model have been examined. Check valve and seal applications show that the model results are in reasonable agreement with the experimental observations.</p>