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Zwick triple offset butterfly valves12/31/2022 ![]() Improper designs can also add to the bearing failures once in service. Furthermore, during the startup phase in new constructions, when pipes have not been properly flushed, debris can migrate into the bearing cavities. Additional situations also attribute to foulings such as simple pipe scale. Other chemical applications such as butadiene and styrene have the same issues as described above, except when these chemicals become trapped and dormant, they cause a phases change and popcorn, or polymerize, resulting in seizing of the bearings. While this is a good design practice, human error has negated this benefit when plant personnel simply turn off the steam to the jacket or unhook the connections to perform some maintenance and do not reconnect the steam or the fittings. Most TOV manufacturers offer a welded-on steam jacket in order to use the steam's latent heat to deliver heat to the bearing area. ![]() ![]() This procedure is not the best practice when operating a modern process facility. When this situation occurs, the end user must apply a heat gun of some sort in order to unlock the valve. This causes the bearing to shaft seizure, locking the disc in position. If the gas-phase sulphur is trapped in the bearing cavities and there is a drop in temperature, the sulphur will become solid. Sulphur in the gas state will have a phase change to a solid in temperatures below 145 F. Many of these problematic situations are obvious, such as sulphur tail gas and acid gas services within refineries and gas processing plants. However, in the world of hundreds of petrochemical, power and other applications, there are many potential problems with bearing failures. In clean services, such as air or water, the chances of the bearings fouling are small. ![]() Additionally, properly designed TOVs should have the bearing located as close as possible to the center line of the disc, which helps deliver a rigid support of the shaft when torqueing into the seat. Therefore, very little shaft deflection can be tolerated in order to properly torque the seal ring in the seat. Properly designed TOVs are metal-to-metal torque seated types of valves. This issue is directly attributed to the need to have metal bearings with very tight tolerances to accept the shaft diameter. Different sealing systems enable an optimal solution for the respective field of application.Bearing failures are the highest root cause of failure in triple-offset butterfly valves (TOVs). The double or triple offset design of the valve disc, high-quality materials and outstanding workmanship ensure safety even in extreme conditions of use. ![]() High operating pressures and extreme temperatures - wherever other resilient seated valves reach their physical limits, this series is the ideal solution. ![]()
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