1, the preface gate valves are normally have single ram, double ram, wedge, the parallel type, such as structure design, including wedge type double ram ( Z42, Z62 series) And the wedge flexible disc ( Z40, Z60 series) The most widely used, the former is closed gate automatically match on both sides of the seat, automatic compensation of wedge Angle processing position error; The latter rely on the gate in the middle of the elastic groove, rely on compensation axial thrust wedge Angle of the valve stem position error processing, both achieve good sealing effect. Is precisely because of its excellent seal on both sides, in some occasions will generate lumen abnormal pressure rise phenomenon, namely when the high temperature and high pressure fluid ( Liquid or gas) If blocked in the valve lumen, upstream side ( See figure 1) Fluid temperature, lumen ( See figure 1) Of heat transfer fluids will be synchronized to rise, with lumen volume not expand and plugging midplane flow from cold to hot, liquid may rapidly vaporized, led to a dramatic increase in stress, higher pressure is often geometric series. The overpressure valve working consequence is very serious. lumen abnormal pressure, the working stress of the pressure and the opening and closing parts ( Such as the use of stem and disc stress) Will increase sharply, driving force of the driving mechanism will be overwhelmed and can't even start, serious when stem snap, gate frame fracture, motor burn out, these phenomena are common in many high pressure large diameter gate, many users often complain that this is the gate 'killed', actually 'killed' the real reason is often lumen abnormal pressure of this 'invisible killer'. Figure 1 lumen abnormal pressure on typical case Z962Y series double wedge type gate valve used in coal-fired power plant water supply system and its bypass, usually this kind of valve in the cold shut down after water pressure test, when the unit when the system temperature rise to 250 ~ 300 ℃, due to temperature rise sharply, closed in the middle of a dramatic increase in the cold water will sync vaporization, make fluid volume increases, pressure increase, at this time if you want to open valve or driving moment is enough big, or stem component intensity is high enough, otherwise often appear stem fracture, ram fracture, ram T slot flowering, fracture, the feed water pump can't start, lead to serious boiler stop outage. 2, abnormal booster damage the formation of abnormal pressure in many applications occur strikingly similar to gate valves, because the two elements of it are similar in many industrial systems, namely the system medium after boot, change from cold to hot; Ram in the cold shut, open when hot. So if nothing is done system, abnormal booster to the destruction of the system is almost inevitable, its harm has three aspects: ( 1) Damage to the valve itself valve body, Industrial Valves cover, and the strength of the valve stem parts take the nominal pressure of the Industrial Valves design its strength, abnormal pressure, the opening pressure will be doubled, and lead to the use of the related parts stress exponentially increases, when the actual stress exceeds the allowable stress, high stress area produces fracture damage, lead to valve cannot open, valve, the machine will be damaged or destroyed. ( 2) Damage to the system security is obvious, shell, the cover such as overpressure, when the pressure is very dangerous, once the overpressure might happen first perforation, the weak positions cause leakage of medium; Its packing and seal parts tend to be rushed out of the high pressure fluid, cause a medium leakage. When the medium is high temperature gas, toxic and harmful gas will be more serious, even will cause harm to the equipment and personnel. ( 3) Caused heavy loss of the control of production process of all kinds of industrial process control is the normal opening and closing of the Industrial Valves key, once this control cannot be achieved, the system paralysis must stop, this will cause huge direct or indirect losses. 3, protective measures from the design, installation, debugging and other aspects, fundamentally eliminate the lumen abnormal booster is entirely possible, inductive commonly used 3 sets of solutions for customers reference: ( 1) Internal valve opening pressure relief hole solve the root of the lumen abnormal pressure is the equilibrium pressure of lumen, the opening of a pressure relief hole is the most economic and efficient solution, shown in figure 2, respectively in the upstream side gate and cylindrical inlet side seat opened a pressure relief hole, of cavity pressure, lumen pressure automatically to the upstream side discharge, always maintain lumen pressure is equal to the upstream side, so as to avoid the occurrence of abnormal pressure. ( a) Ram pressure ( b) Brake pressure
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