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Reasons for leakage: 1. Leakage from the valve body and valve cover: ① Poor manufacturing quality, with defects such as sand holes, loose structures, and inclusions in the valve body and valve cover itself; this is common in cast iron valve components； The welding is poor, with issues such as slag inclusions and incomplete penetration. ②Heavens freeze and crack. ③The welding is poor, with slag inclusions. Defects such as incomplete welding and stress cracks. ④The cast iron valve was damaged after being struck by a heavy object. II. Leaks at the packing area: ① The wrong type of packing was selected; it cannot withstand corrosion by the medium, nor high pressure or vacuum, nor high or low temperatures. ②The filler is not installed correctly. ③The filler has exceeded its service life, has aged, and lost its elasticity. ④The valve stem is bent, and there is corrosion and wear. ⑤Insufficient number of packing rings, and the gland is not tightened properly. ⑥Damage to the gland, bolts, and other components is why the gland cannot be tightened. ⑦Improper operation, excessive force, etc. ⑧The gland is skewed, and the gap between the gland and the valve stem is either too small or too large, resulting in wear of the valve stem and damage to the packing. III. Leakage at the gasket area: ① The wrong type of gasket was used; it cannot withstand corrosion by the medium, nor high pressure or vacuum, nor high or low temperatures. ②Unstable operation causes fluctuations in valve pressure and temperature. ③The pressure of the gasket is insufficient, or there is no pre-tightening clearance at the connection. ④The gasket is not properly assembled, resulting in uneven stress distribution. ⑤The machining quality of the static seal surface is poor; the surface is rough and has radial scratches. The sealing surfaces are not parallel to each other. ⑥The static sealing surface and gasket are not clean, with foreign objects mixed in. IV. Leakage at the sealing surface ① The sealing surface is not properly ground, preventing the formation of a tight seal. ②The tip at the connection between the valve stem and the closing element is suspended, misaligned, or worn. ③The valve stem is bent or misassembled, causing the closing element to be skewed or out of alignment. ④If the material of the sealing surface is not selected appropriately, or if the valve is not chosen based on the operating conditions, the sealing surface is prone to corrosion, erosion, and wear. ⑤Cladding and heat treatment were not carried out in accordance with the procedures; wear occurred due to low hardness, corrosion resulted from alloy-related factors, and cracks appeared as a result of excessive internal stress. ⑥The surface-treated sealing surface may peel off or lose its original properties due to excessive grinding. ⑦Erosion occurs due to improper closure of the sealing surface or fine gaps that appear after closure as a result of cold shrinkage. ⑧When a cut-off valve is used as a throttle valve or pressure reducing valve, its sealing surfaces are eroded and damaged. ⑨The valve has reached the closed position; continuing to apply excessive closing force, including improper use of long rods or long wrenches, causes the sealing surfaces to be damaged and deformed. ⑩Excessive wear on the sealing surface leads to a loss of seal, meaning that the sealing surfaces fail to fit together properly. V. Leakage of seals ① The seal is not properly rolled. ②The sealing ring is poorly welded or surfaced-welded to the main body. ③The threads, screws, and retaining rings connecting the seal ring are loose. ④The sealing ring connection surface is corroded. VI. Leaks caused by the detachment of the closing element: ① Improper operation leads to the closing element getting stuck or moving past the top dead center, resulting in damage and breakage at the connection points. ②The closing element is not securely connected and becomes loose, falling off. ③The wrong material was chosen for the connectors, which cannot withstand corrosion from the medium and mechanical wear. VII. Leakage due to foreign objects embedded in the sealing surface ① Sealing surfaces that are not opened or closed frequently are prone to accumulating dirt. ②The medium is dirty, containing particles such as abrasives, rust, and welding slag that get stuck on the sealing surface. ③The medium itself contains hard particles. Prevention and elimination methods 1. Leakage of the valve body and valve cover: ① Improve the quality of casting, and conduct strength tests strictly in accordance with regulations before installation. ②Cast iron valves with temperatures at or below zero degrees should be insulated or heated; valves that are no longer in use should have any accumulated water removed. ③The welds of the valve body and valve cover, which are formed by welding, shall undergo flaw detection testing and strength testing after welding. ④It is prohibited to stack heavy objects on valves, and it is not allowed to strike cast iron and non-metallic valves with a hammer. II. Leakage at the packing area: ① The material and type of packing should be selected based on the operating conditions. ②Reinstall the packing. ③Replace the packing in a timely manner. ④Make corrections and repairs. ⑤As per the specifications, the required number of turns must be completed; the gland should be compressed symmetrically and evenly, with an adequate preload gap left. ⑥Repair damaged parts promptly. ⑦Operate with even and normal force; the use of long rods or long wrenches is not allowed. ⑧The gland bolts should be tightened evenly and symmetrically. If the gap between the gland and the valve stem is too small, it should be increased appropriately; if the gap is too large, the gland should be replaced. III. Leakage at gaskets: ① The material and type of gasket should be selected according to the operating conditions. ②Carefully adjusted for smooth operation. ③The bolts should be tightened evenly and symmetrically, with the preload meeting the specified requirements – it must not be too high or too low. There should be a pre-tightening clearance at the flange and threaded connections. ④The gaskets should be fitted properly so that the load is distributed evenly; overlapping gaskets or the use of multiple gaskets is not allowed. ⑤If the static seal surface is corroded, damaged, or of poor machining quality, it should be repaired and ground, and a coloring inspection should be carried out to ensure that the static seal surface meets the relevant requirements. ⑥Care should be taken to keep the gaskets clean when installing them; the sealing surfaces should be cleaned with kerosene, and the gaskets must not touch the ground. IV. Leakage at the sealing surface ① When grinding the sealing surface, appropriate tools, grinding agents, sandpapers, and other materials should be used, and the grinding method must be correct. After grinding, a coloring inspection should be carried out to ensure that there are no defects such as dents, cracks, or scratches on the sealing surface. ②The connection between the valve stem and the closing element should meet the design requirements; if the tip of the stem does not meet these requirements, it must be adjusted. There should be a certain amount of play at the tip, especially with an axial clearance of no less than 2 mm between the shoulder of the valve stem and the closing element. ③The bent valve stem should be straightened; after adjustment, the valve stem, valve stem nut, closing element, and valve seat should all be on the same common axis. ④When selecting valves or replacing sealing surfaces, they must meet the operating conditions; after processing, the sealing surfaces should possess good properties in terms of corrosion resistance, wear resistance, and scratch resistance. ⑤Remelt welding and heat treatment must be carried out, with no defects that could affect performance allowed to exist. ⑥The surface of the sealing face is quenched, nitrided, borided, and chromium-plated. ⑦Valves should be marked to indicate whether they are closed or open, and those that are not sealed properly should be repaired promptly. When cracks appear due to cold shrinkage, it should be tightened again. ⑧As a shut-off valve, it must not be used as a throttle valve or pressure reducing valve; the closing element should be in either the open or fully closed position. ⑨The closing force of the valve should be appropriate; for handwheels with a diameter of less than 320 mm, operation by one person only is permitted, while for handwheels with a diameter of 320 mm or more, operation by two persons is allowed, or operation by one person using a lever within 500 mm in length. ⑩Once wire pulling occurs on the sealing surface, it should be adjusted; if adjustment is not possible, it should be replaced. V. Leakage of the sealing ring: ① Inject adhesive or re-press to secure it. ②Reweld it; if rewelding is not possible, the original surfacing layer should be removed and resurfaced. ③ It should be cleaned, the damaged screws replaced, and reassembled. The grinding seal ring fits tightly with the connection seat. Those severely corroded can be repaired using methods such as welding or bonding. ④It can be repaired using grinding, bonding, or welding methods; if repair is not possible, the seal ring should be replaced. VI. Leaks caused by the detachment of closing components ① Do not apply excessive force when closing the valve; when opening it, do not go beyond the upper dead center. After the valve is fully open, turn the handwheel 1/4 to 1/2 turn in the opposite direction. ②The closure element should be connected to the valve stem in a proper and secure manner, and a backstop should be provided at the threaded connection. ③Re-select the connectors. VII. Leakage due to foreign objects embedded in the sealing surface ① Improve maintenance. Close and open the valve, leaving a small gap when closed; repeat this several times to allow the fluid to carry away the deposits. ②Use fluid to flush away debris; for those that cannot be removed by the fluid, open the valve cover to take them out and repair them. ③Where possible, plug valves, ball valves, and valves with soft-seated surfaces should be selected.