Resolving gasket- and bearing failure in a TBV96S valve

Abstract

This report is the bachelor thesis in the mechanical engineering study with specialization in Design of Marine Structures, and addresses bearing and gasket failures with the valve TBV96S which is constructed by Valves of Norway. The task is given by Valves of Norway a valve producing company located by the west coast of Norway, outside Bergen. Related to the gasket and bearing problems, the assignment also is to nd the reason for the failures and the modi cations needed to avoid these. The components a ected by the changes will be stress analyzed with both hand and computer aided calculations. Lastly a mount will be designed for this speci c valve. The TBV96S valve is used for mud and has a problem with leakage between the seat and the ball inside the valve. The reason for the leakage was found to be that the hardness rating of the gasket was to low to handle the corrosion from the hard particles in the mud. This was found through examining the failed valve, and researching the materials used for gaskets. The material that is recommended for further use in the valve is PEEK. The damaged bearings on the stem and trunnion is found to be overloaded from both the work pressure and from the actuator force. A new material is assigned to the bearings, a woven PTFE reinforced and bonded to metal backing from TENMAT called FEROGLIDE. A maximum actuator force is then found through several nite element analysis. Further a mount is designed to counteract the friction torques generated by the gasket and bearings. The mount is designed for simplicity and low cost. It will convert the linear motion from the actuator to a rotational motion on the stem. The design is presented using 3D renderings and 2D drawings. In case of a situations where a higher safety factor or a smaller arm is needed several proposals for mounts that will cancel out the actuator force are suggested.