Study Of The Sealing Characteristics Of Hard Seal Fixed Ball Valves Under Two Given Operating Conditions

A hard-seated fixed ball valve is a valve in which both the seat and the ball are made of metal,and the ball remains fixed and can only be turned within 90° without movement.As a type of hard-seated ball valve,it has the advantages of good sealing,easy operation,low flow resistance and high reliability,but because its ball remains fixed,its bore is usually much larger than that of an ordinary ball valve,giving it a higher flow rate,greater corrosion resistance and a wider temperature range.At the same time,because of its large bore,its material hardness is greater and the sealing pressure required to achieve a seal is much higher than that of a normal ball valve.Therefore,under complex operating conditions,under the combined effect of temperature,pressure,corrosion,wear and other factors,hard-seated fixed ball valves are prone to seal failure between the seat and ball,resulting in leakage.To this end,a comprehensive analysis of the hard seal fixed ball valve in a variety of operating conditions,the study of its sealing characteristics under the given operating conditions,to help the ball valve research,design and optimisation.According to the company’s needs,this project selects the Class900 NPS24 hard seal fixed ball valve as the research object and investigates its sealing characteristics under the given two working conditions.Firstly,Solidworks 3D software was used to model the parts of the ball valve based on the 2D drawings obtained from the measurements,and the assembly module was used to complete the assembly,followed by a theoretical analysis of the main components and the actual working conditions of the valve as a whole.For accuracy and speed of calculation,the ball valve was selected for simplification prior to finite element analysis.Given its use as a shut-off valve,it was chosen to perform the force analysis in the closed state,so that the forces were applied according to the forces in the closed state.Finally,the finite element software ANSYS analysis is used to obtain the stress and strain clouds under the given two operating conditions,and the leakage situation is analysed through the permeation and gap clouds to determine the sealing characteristics under the given two operating conditions.The Static Structure module was used for the analysis in the ambient and high pressure conditions,while the Static Structure and Transient Structure modules were used for the analysis in the high temperature and high pressure conditions with thermosolid coupling.It was found that in the ambient and high pressure conditions,the sealing surface of the ball valve leaks slightly at both the macro and micro levels,resulting in sealing problems;in the high temperature and pressure conditions,the ball valve leaks only at the macro level,but not at the micro level.The relationship between the modulus of elasticity of the coil,the radius of the coil and the axial projection of the sealing surface is analysed by varying the modulus of elasticity of the coil,the radius of the coil and the axial projection of the sealing surface.Under both conditions,the maximum permeation and minimum clearance tend to coincide with the change in coil modulus,radius and axial projection of the sealing surface.Within a certain range,changing the radius of the ball is better for improving the sealing effect of the ball valve than changing the modulus of the spool and the axial projection of the sealing surface.Increasing the radius of the ball significantly improves the force conditions and effectively reduces the leakage area.When the radius is R=454 mm,the maximum penetration and maximum clearance values under both operating conditions are minimised and leakage is less likely to occur,resulting in a good sealing effect.However,increasing the ball radius will result in an increase in cost,so a further attempt was made to increase the seat hardness by reducing the hardness of the seat to improve the fit between the seat and ball without increasing the hardness of the ball using the traditional method.Finite element analysis showed that this optimisation increased the contact area between the fluid and the seat,improved the contact between the contact surfaces and reduced the maximum penetration and maximum clearance values.Without increasing the amount of material,the opening leakage problem of the original design is effectively solved and the sealing characteristics of the ball valve are improved.