Stainless steel valve stem the root cause of the rupture, deformation

by:AIRWOLF     2020-05-24
Stainless steel valve stem of the root cause of the rupture, deformation of stainless steel gate, the gate, as with the stem straight line usually in lifting lever on the trapezoidal thread, through the valve at the top of the nut and guide groove on the valve body, the rotary motion to linear motion, which is the operating torque thrust into operation. Sealing surface can only rely on medium pressure to seal, that is, to rely on medium pressure to press the sealing face of gate to the other side of the seat to ensure sealing face seal, this is the seal. Most is adopt compulsory seal gate valve, the valve is closed, to rely on outside force forced the ram pressure to the seat, to ensure the sealing surface sealing. Gate valve with its pressure, heat resistance, High and low temperature) , corrosion resistance, A variety of material configuration) , have two-way sealing function, wear resistance, and the advantages of long service life is more and more widely used in all kinds of industrial system, open and closed, the medium for the system's stability and control play an important role. Stainless steel valve stem fracture analysis: stem fracture usually occurred in the thread root, the minimum sectional area and is easy to appear stress concentration and the phenomenon of excessive. Especially when working conditions significantly deviate from the design parameters. After gate valves open the valve stem ladder type screw thread relief groove snap accident. The survey found that the valve bonnet nut loose, cover up, stem nut jammed, obviously this is a debug denso trip, protect too much torque caused by the accident. Another type of valve stem fracture accident happened in open moment. Show the ram is not out of the seat, the valve stem is under or on the thread root fracture. The reason for this is usually attributed to ram gets stuck, this is just part of the reason or secondary causes. One important reason is that following the closure of the valve body lumen abnormal booster, when the valve is turned off, closed between upstream and downstream sides sealing surface midplane fluid pressure is much higher than the upstream pressure. There are two reasons for this phenomenon. One lumen fluid heated by upstream fluid heating expansion, result in higher pressure drastically. A second gate closing moments fluid sealed in the lumen, unable to drain, lumen space was further squeeze stem, due to the compressibility of the liquid is very limited, also can make pressure surge, this phenomenon is especially easy to occur in power plant water supply gate valves. At the same time, the abnormal pressure in general will increase in geometric series, far more than the stem strength design limit. Stainless steel valve stem deformation analysis: stem bending generally appear in denso debugging is not at the time of electric valve, such as closing torque too big and not set trip protection or disorders, such as the damage to the valve is very big.
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