Numerical Analysis Of Specific Pressure Of Lined Ball Valve Sealing Technology

1. Overview: COSMOSWORKS is a design and analysis system fully integrated into SOLIDWORKS. It provides pressure, frequency, constraint, thermal, and optimization analysis, offering designers a comprehensive analytical tool within the SOLIDWORKS environment. This article focuses on the Lined Ball Valve seat. In the valve seat engineering design process, the total force acting on the seat sealing surface and the sealing pressure ratio are calculated using empirical or modified formulas in actual design. These two parameters are difficult to accurately measure using existing methods. By using COSMOSWORKS finite element analysis software to calculate the sealing pressure ratio of Lined Ball Valve under simulated operating conditions and comparing it with theoretical calculation formulas, this provides a relatively accurate reference for valve design.

2. Solid Modeling: Taking the design of the Lined Ball Valve with a DN of 239 mm and a PN of 25 MPa as an example, the various components of the Lined Ball Valve are first solid modeled in SOLIDWORKS and assembled. Interference checking is performed on the assembly to obtain an assembly without interference between parts.

3. Finite Element Analysis

3.1. Sealing Mechanism

Lined Ball Valve uses an inlet seal. At this time, the ball valve pressure differential (P-P1) is greater than 0 (P and P1 are the fluid pressures in the valve inlet and center chambers). When the pressure differential reaches a certain level, that is, when a certain compression ratio is generated on the sealing surface, this pressure ratio will cause the valve seat to elastically deform, filling microscopic irregularities on the sealing surface and preventing fluid from passing through the seal. When the pressure differential is small or the valve seat is made of metal, the pressure differential alone cannot achieve complete sealing. In this case, an external sealing force must be applied to increase the compression ratio. The empirical formula for calculating the required sealing pressure qb based on the operating pressure is qb = 1.2PN = 30MPa. To ensure reliable sealing of the ball valve, a sufficient pressure ratio should be maintained on the contact surface between the ball and the valve seat, but it must not exceed the allowable pressure ratio [q] of the sealing material. The theoretical sealing pressure ratio q1 is:

3.2. Finite Element Calculation: Since the sealing pressure ratio calculation process only involves components such as the ball, valve seat, and valve seat support ring, the finite element analysis model has been simplified. This not only saves computer resources but also improves the accuracy of the calculation results. By simulating real-world operating conditions, the pressure value Qs on the contact surface between the valve seat support ring and the left and right bodies must be calculated. Based on the actual operating conditions, a static analysis case was created in COSMOSWORKS, and the constraint load conditions were determined.
(① Fix the contact surface between the sphere, upper stem, and bottom cover. ② Limit the valve seat and seat support ring to axial movement only. ③ Apply Qs to the contact surface between the seat support ring and the left and right valve bodies and perform meshing. ④ Ensure that the material of the sphere and seat support ring is 35# steel, and the material of the valve seat is austenitic stainless steel, with no sliding between the sealing surfaces (the allowable specific pressure [q] value of austenitic stainless steel is 150 MPa). Click Run. The calculation results are shown in Figure 3c.

3.3 Extraction Results
Equidistantly spaced on the valve seat sealing surface 25 points were acquired and pressure values ​​were measured at these points sequentially along the X-axis. The data was then imported into Excel for analysis. The results showed that the sealing pressure distribution along the valve seat sealing surface showed a parabolic distribution, with a maximum value of 62.1 MPa at the inner diameter of the valve seat and a minimum of 40.16 MPa at the center of the valve seat. Considering the valve seal design parameters for the required pressure distribution qb (30 MPa) and the allowable pressure distribution of the valve seat material [q] (150 MPa), the sealing pressure distribution fell between qb and [q], meeting the design criteria.

4. Conclusion
Because the valve seat and the ball sealing surface are relatively fixed during the sealing process, they cannot be moved. Therefore, after being subjected to preload and fluid pressure, the inner diameter of the sealing ring has a smaller axial deformation margin relative to the middle part, and is subjected to a larger extrusion force. The radial deformation margin of the sealing ring is larger than that of the middle part, and is subjected to a relatively smaller extrusion force. In addition, although the ball is in contact with the valve seat, there is a fluid medium due to the capillary phenomenon. When the ball moves relative to the valve seat along the flow direction, the ball and the valve seat are in closer contact, and the fluid medium from the edge to the middle of the sealing surface becomes less and less. Therefore, the edge of the sealing surface is under the dual action of the medium and the ball, and the force is slightly greater than that in the middle of the sealing surface. Therefore, the sealing pressure ratio on the sealing surface is parabolically distributed. On the edge annular surface, due to the preload and the force exerted by the medium The combined effects of the pressure and the metal sphere produce a fluctuating curve, with a particularly significant effect at the outer diameter of the sealing surface. Due to capillary phenomena, it's reasonable to use the sealing pressure at the center of the sealing surface as the sealing pressure for the entire trunnion-mounted ball valve. Figure 5 shows a pressure value of 40.16 MPa at the center of the sealing surface, while the theoretically calculated sealing pressure is 40.17 MPa. The difference between the two is 0.01 MPa, with an error of less than 3%. This demonstrates that the sealing pressure of the trunnion-mounted ball valve calculated using finite element analysis is reliable. Furthermore, it fully reflects the distribution of sealing pressure across the entire valve seat, providing a reliable basis for overall valve design.