Gate valve stem fracture or deformation

Gate valve with its pressure, temperature (high temperature), corrosion-resistant (a variety of material configuration), with two-way sealing function, wear resistance and long service life, etc. more and more widely used in various industrial systems, the realization of medium Of the opening and closing of the system for the stability and control has played an important role. Gate valve stem fracture fracture occurred in the upper and lower thread root, the smallest cross-sectional area here, prone to stress concentration and excessive phenomenon. Especially when working conditions deviate significantly from the design parameters. Such as a power plant has repeatedly DN150 electric gate valve opened after the thread tracheal thread retractable groove pull off accident. The survey found that the valve cover preload nut loose, valve cover up, stem nut stuck, it is clear that this is the electrical installation of debugging over, the protection of torque caused by an accident. Another type of stem breakage occurs at the moment of opening. The performance of the gate has not yet out of the valve stem, the stem that is in the upper or lower thread root fracture. The reason is usually considered to be stuck in the gate, which is only partly or partly due to reasons. An important reason is that after the valve cavity is closed, the pressure in the cavity fluid is much higher than that of the upstream pressure, that is, the pressure of the fluid in the cavity enclosed between the sealing surfaces on the upstream and downstream sides after the valve is closed. There are two reasons for this phenomenon. One of the cavity fluid is heated by the upstream fluid to heat up and expand, causing the pressure to increase drastically. The second gate closed the moment the fluid closed in the cavity, can not drain, cavity space is further squeezed by the stem, due to the liquid compressibility is very limited, but also make the pressure surge, this phenomenon is particularly prone to power plants Z962 main feed water gate valve. At the same time, the abnormal boost will generally increase geometrically, far exceeding the design limit of stem strength. Gate valve stem deformation Valve stem bending generally occurs when the electric valve electric debugging improper, such as the closing torque is too large and there is no travel protection or disorders, the damage to the valve is very large.