Modeling of deformation processes in a valve

Abstract

A set of issues on computer modeling of valve deformation processes at lower temperatures are reviewed in the publication. Some types of valves which are used to shut off fluid flows are exposed to jamming. The problem relates to valves with a solid rigid wedge. It is often show up with temperature drop down to negative values. The valve electric drives have enough power, thus combining with the presence of gearboxes it creates a force, that sometimes leads to a breakage of the valve stem on the opening process. The purpose of the work is to define the influence of geometric and physical parameters in the valve on the development of deformations and thermal stresses resulting in jamming. To determine the jamming cause, an analysis of various options was made. The options include the occurrence of deformations of structural elements which are associated with the processing technology of the adjacent surfaces of the wedge and saddle, using various materials, and calculations of the deformation processes for some simple structures were performed. Mathematical modeling was performed using the finite element method. Due to the slow change in ambient temperature, stationary three-dimensional models were used for calculations. The temperature change is set in the issue through the fixed differential. The design features of valves with a hard wedge require careful machining to ensure a tight fit and eliminate leaks. Due to the complexity of access to the internal cavity of the valve for processing, a collapsible design is provided, which allows to achieve high quality surfaces and to avoid jamming. The use of different grade steels and the possibility of surface hardening during machining leads to a difference in physical properties such as coefficient of thermal expansion. However, according to the calculations, with the small thickness of the parts and the hardening depth, the influence of coefficient of thermal expansion isinsignificant. Another reason for the difference in strain is the difference in elongation of the rod and the cylindrical shell. In the given temperature range for materials with low coefficients of thermal expansion, the difference in the geometric measurements turned out to be low and comparable with the calculation error. The study of the geometric shape influence on the relative deformations of the valve elements demonstrated that the use of cylindrical shells and continuous cylinders in the design do not lead to the development of thermal stresses. Even the shape of the wedge does not affect the magnitude of the deformations. However, the production of the vertical part of the body in a conical shell shape leads to the appearance of significant deviations in the deformation magnitude of the mating surfaces. In the actual valves, the body has a more complex shape, but the size ratio corresponds to the simplified model considered before. Conclusion: to avoid jamming, the design must be symmetrical. Since this solution is more material-intensive, it is required to equip the valves with heating systems to balance deformations.