Vibration Analysis And Improvement Research On Closing Process Of Large Diameter Wedge Gate Valve

At present,large diameter gate valves have new requirements in the global thermal power,nuclear power,hydropower and petrochemical fields and need to deal with more stringent working conditions.Large diameter wedge gate valve has the characteristics of easy manufacture,low flow resistance and long-term safe and stable operation,so it is widely used in metallurgical industry,power generation industry,petrochemical industry and other fields.However,the valve body of the large diameter gate valve is large,and the shape of the inner cavity section is irregular,so it is difficult to use the empirical formula to accurately design the large diameter wedge gate valve.The valve stem vibrates violently and breaks during the closing process of a large diameter wedge gate valve designed by an empirical formula in Zhejiang province.Scholars at home and abroad have made corresponding studies on the stress,strain and switching torque of large diameter valves,and have also done some research on the vibration caused by the coupling of fluid and structure in the valve during the closing process.however,the research is usually done on the structure of the valve plate and the valve body,but there is little research on the vibration reduction improvement scheme of adding parts after the valve.Therefore,in view of the above problems,this paper carries on the ANSYS numerical simulation calculation for the closing process of the large diameter wedge gate valve with1200 mm caliber.The main research work and conclusions are as follows:(1)In view of the long closing process of large diameter gate valve,the discrete analysis method is adopted.The steady flow field of the large diameter wedge gate valve with different opening during the closing process is found to be in progress with the closing process.It will cause the fluid to be detained at the front of the gate under the influence of river closure,and change the direction of the fluid and reduce the velocity of the fluid due to the action of the gate,resulting in large eddy current and reflux in the low pressure area behind the valve.According to the results of steady-state flow field calculation,the transient flow field is calculated,and the transient pressure pulsation characteristics are obtained by monitoring the pressure in front of the valve and behind the valve,and the pressure pulsation frequency domain characteristics under different valve plate positions are obtained by fast Fourier transform.It is found that the pressure pulsation is mainly concentrated below 50 Hz,which provides a research basis for the follow-up thermo-fluid-solid coupling vibration analysis.(2)The stress-strain law of large diameter wedge gate valve under thermal fluid-solid coupling in the process of closing is simulated and analyzed.through the study,it is found that the stress and strain at all openings in the closing process meet the stress check standard of the valve.it is further explained that the large diameter wedge gate valve designed according to the empirical formula meets the design standard.at the same time,the natural frequency of the stem and plate system at each position in the closing process is obtained by modal analysis.Then the resonance characteristic under the small opening is obtained by using the harmonic response analysis,and it is found that the large diameter gate valve is easy to produce larger resonance amplitude under the small opening,which provides the basis for the follow-up vibration reduction and vibration suppression improvement scheme,and is verified by the empirical formula.the reliability of the simulation is further proved.(3)In order to solve the problem of large resonance amplitude of large diameter wedge gate valve under small opening,a method of adding pipe expansion to improve the characteristics of liquid flow system is put forward.By designing three different pipe expansion sizes to compare the flow field characteristics before and after improvement and the vibration characteristics without damping and damping,the most effective vibration suppression scheme is explored.Finally,it is found that it is most suitable to add pipe expansion with 1 times DN length and 1.3 times DN diameter after the valve.It provides a basis for the design and research of large diameter wedge gate valve in vibration direction.