Analysis Of Flow Characteristics And Sealing Performance Of Super Large Diameter Fully Welded Ball Valve

All-welded ball valves are widely used in long-distance pipelines such as urban heating and natural gas transportation due to their simple structure,burial,and long service life.Considering that it is more economical to build a large-diameter pipeline than multiple parallel small-diameter pipelines,there is an increasing demand for super large-diameter fully welded ball valves with a nominal diameter of 1400 mm and above in the construction of major national pipeline projects.The good sealing performance guarantees the safety of the ball valve in use.The sealing performance of the fully welded ball valve is determined by the sealing specific pressure on the contact surface of the valve seat sealing ring and the ball core.If the seal specific pressure is too large and exceeds the allowable specific pressure of the sealing material,the seal ring may be crushed,which may lead to seal failure;if the seal specific pressure is less than the required specific pressure for the seal,the ball valve will leak directly.At present,the research on the sealing performance of ball valves takes the medium pressure as a static load,and analyzes the distribution of the specific pressure of the sealing surface of the ball and the valve seat under full operating conditions.However,during the opening and closing process of the ball valve,the internal flow field is complicated,and phenomena such as vortex and water hammer will occur.The pressure of the fluid medium acting on the sealing ring is constantly changing.Only through static analysis,the sealing specific pressure during the opening and closing process of the valve cannot be obtained.The size and the law of change cannot accurately determine the sealing performance of the ball valve during the opening and closing process.This topic takes DN1400 PN2.5 extra large diameter fully welded ball valve as the research object,and analyzes the internal flow field flow characteristics and seal specific pressure distribution of the ball valve at different opening degrees through numerical simulation.Analyze the sealing performance of the ball valve during the whole process of opening and closing according to the seal specific pressure distribution of the valve seat sealing surface,and improve the structure of the valve seat sealing ring accordingly.The specific research content is as follows:(1)Analysis of the flow characteristics of the ball valveUse Fluent software to simulate the internal flow characteristics of the ball valve at different openings,obtain the velocity distribution cloud map and pressure distribution cloud map in the flow field,and calculate the flow coefficient and flow resistance coefficient of the ball valve at different openings.The results show that the high-speed flow area of the ball valve in the opening process is mainly concentrated at the inlet and outlet of the valve core,and vortices are formed inside the valve core and the rear end of the valve,and the size of the vortex decreases with the increase of the valve opening;when the opening degree reaches 45°,the flow resistance coefficient is very large,and the flow coefficient is very small.Before the opening degree of the ball valve reaches 45°,the flow coefficient increases slowly but the flow resistance coefficient decreases sharply;when the opening degree reaches 45°,the flow coefficient increases rapidly.When the ball valve is fully opened,it reaches the maximum value;while the flow resistance coefficient decreases slowly and reaches the minimum value when it is fully opened.(2)Research on the sealing performance of ball valvesThe fluid-solid coupling method is used to analyze the law of the change of the operating seal specific pressure of the valve seat sealing ring and the ball contact surface with the ball valve opening.The analysis results show that: during the opening and closing process of the ball valve,the maximum sealing specific pressure under different opening degrees is mainly concentrated at the junction of the contact surface;the maximum sealing specific pressure is formed near the 75° opening.If the sealing specific pressure is too small,it cannot meet the requirements of the sealing performance,and the sealing structure of the ball valve is improved.(3)Improvement of ball valve sealing structureBy analyzing the reasons why the seal specific pressure is too small,a double-inclined surface and spherical core contact sealing structure is proposed,and the seal specific pressure is recalculated.The analysis results show that the improved seal specific pressure has increased,and the minimum seal specific pressure of the seal ring at the inlet end has increased from1.635 MPa to 3.529 MPa,which is within the required specific pressure and allowable specific pressure range for the seal.The pressure sealing test was carried out through the test equipment,and the test results showed that the redesigned ball valve sealing structure meets the sealing requirements.