Visualization Of Vibration And Cavitation In Pressure Regulating Poppet Valves

Poppet valve is made up of poppet,seat and spring,which is one of the most commonly used valve structure in hydraulic technology for adjusting and limiting system pressure.In hydraulic system,the instability vibration appears frequently and the pressure fluctuations can be as high as ± 5MPa.The principle of instability vibration is still unclear so that this phenomenon seriously affects the reliability and the adjustable precision.The poppet vibration of the direct pressure regulating valve will directly lead to the pressure fluctuations in hydraulic system and the instability phenomenon is mainly caused by pilot valve in multistage pressure regulating valve.Consequently,the study on the vibration and cavitation of the pilot valve is very typical and meaningful for both the direct pressure regulating valve and pilot pressure regulating valve.In this paper,fluid-structure interaction calculation and visualization experiment are used to study the axial vibration and flow field of the different poppet valves.Through the fluid-structure interaction calculation of the poppet valve with damping hole,it is found that the poppet surface can be divided into two areas with different dynamic characteristics: the jet impingement area and the static pressure area.In the jet impingement area,the phase of pressure lags behind the phase of valve lift.However,the static pressure area shows the opposite.The hydraulic force generated in jet impingement area can increase the axial dynamic damping of the poppet when the pressure fluctuation of the two areas can be compensated reasonably.When instability vibration happening,there is no negative damping force generating on the poppet surface.Although the hydraulic force in jet impingement area can still increase the dynamic damping of the poppet,the amplification effect on the pressure fluctuation amplitude of the large static area can keep the poppet vibrating violently.Through the visualization experiment,it is found that the instability of the poppet can be divided into three types of impact seat,non-impact seat and transition state.The mode of vibration is related to the flow rate.Drastic cavitation happens when the poppet impact the seat even the inlet pressure is lower than the pressure of the cavitation inception.By the way,the bubbles collapse and the springback happens because of the instantaneous break at the port.Through the analysis of the frequency of the poppet displacement and the system pressure,it is found that the frequency of the poppet vibration is up to the natural frequency of the pipe system during the valve opening process.Besides,all the compressibility of working medium,the flow(pressure)pulsation from the pump and the coupling vibration of the pipe can lead to poppet instability vibration.This paper reveals the axial vibration type of the poppet and its flow field instantaneous characteristic,and obtains the key factors leading to the poppet instability vibration.This research results have important theoretical and practical value to improve the stability of pressure regulating valve.The main content of the paper is as follows:1.The vibration of the poppet with the damping hole is simulated by fluid-structure interaction which under the external disturbance.Pressure distribution of the poppet surface and its variation rule are analyzed,and the main reasons for the strong stability of the poppet with damping hole are revealed.By comparing the characteristic of different flow fields(the poppet and body are different),the key factors affecting the jet impact are obtained.Meanwhile,the instability vibration of poppet caused by the compressibility of the medium is simulated based on the experiment condition,the dynamic mechanism for the poppet keeping great vibrating are revealed.2.High speed video technology is used to observe the vibration and flow field in valve.Two kinds of poppet body(with and without damping hole)are used in the experiment to study the mode of instability vibration and characteristics of instantaneous flow field.The relationship of the instability mode and flow rate is obtained.3.The method of spectrum analysis is used to analyze the vibration during the poppet opening process.The key motivator of the vibration during the adjusting process is obtained.The frequency signals of system pressure and poppet displacement are studied,and the main reason for the instability vibration is obtained.