Reasons for gate valve stem breakage or deformation

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Gate valve with its pressure, temperature (high and low temperature), corrosion resistance (a variety of material configurations), with two-way sealing function, wear resistance and long service life, etc. are increasingly widely used in various industrial systems, to achieve the opening and closing of the medium, for the stability of the system and the control of the play an important role.

Gate valve stem fracture generally occurs in the upper and lower threaded root, where the cross-sectional area is the smallest, prone to stress concentration and overrun phenomenon. Especially when the working conditions deviate greatly from the design parameters. Such as a power plant has repeatedly occurred DN150 electric gate valve after opening the valve stem trapezoidal thread back cutter groove at the pull off the accident. Investigation found that the valve cover pre-tightening nut loose, the valve cover upward, the stem nut stuck, apparently this is the electrical installation trip debugging over the position, the protection torque is too large caused by the accident.

Another type of stem fracture accident occurred in the opening moment. Manifestation of the gate is not yet out of the valve seat, the stem that is in the upper or lower threaded root fracture. The cause is usually considered to be the gate stuck, which is actually only part of the reason or secondary reasons. An important reason is that the valve body cavity after the closure of the abnormal pressure, that is, after the valve is closed, closed between the upstream and downstream sides of the sealing surface of the cavity fluid pressure is much higher than the upstream pressure phenomenon. There are two reasons for this phenomenon. First, the fluid in the cavity is heated by the upstream fluid expansion, resulting in a sharp rise in pressure. The second gate closure instant fluid closed in the cavity, can not flow out, the cavity space is further squeezed by the valve stem, due to the compressibility of the liquid is very limited, will also make the pressure increase, this phenomenon is especially easy to occur in the power plant Z962 class main water gate valve. At the same time, its abnormal pressure will generally increase geometrically, far more than the stem strength design limit.

Gate valve stem deformation stem bending generally occurs in the electric valve electrical installation commissioning is not when, such as closing torque is too large and not set up trip protection or out of adjustment, etc., its damage to the valve is very large.

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