Body and bonnet leakage causes: 1, cast iron casting quality is not high, the valve body and valve body with trachoma, loose tissue, slag and other defects; 2, days cold cracking; 3, poor welding, there is a clip Slag, welding, stress cracks and other defects; 4, cast iron valve damaged by heavy objects impact. Maintenance methods: 1, to improve casting quality, strictly in accordance with the provisions of the pre-installation strength test; 2, the temperature at 0 ℃ and 0 ℃ below the valve should be insulated or mixed hot, stop using the valve should exclude water; The weld of the valve body and bonnet consisting of welding shall be carried out according to relevant welding operation rules and the flaw detection and strength test shall also be carried out after welding. 4) It is forbidden to push heavy objects on the valve, Metal valves, large-diameter valve should be installed bracket. Leakage at the filler valve leakage, packing accounted for the largest proportion. Reason: 1, the choice of filler, impatient medium corrosion, impatience valve high pressure or vacuum, high temperature or low temperature use; 2, packing is not installed, there is a small generation, poor spiral wound joints, ; 3, the filler over the service life, aging, loss of flexibility; 4, valve stem accuracy is not high, there are bending, corrosion, wear and other defects; 5, packing ring is insufficient, the gland is not compressed; 7, improper operation, excessive force, etc .; 8, gland skew, gland and the gap between the valve stem is too small or too large, resulting in stem wear and tear, packing damage. Maintenance methods: 1, should be selected according to the conditions of packing materials and types; 2, according to the relevant provisions of the correct installation of packing, packing should be compacted circle by ring, the joint should be 30 ℃ or 45 ℃; 3, 4, the valve stem bending, wear should be straightened, repair, serious damage should be promptly replaced; 5, the packing should be installed according to the number of laps, glands should be symmetrical uniform Should be tight, pressure sleeve should be more than 5mm preload gap; 6, damaged gland, bolts and other parts, should be promptly repaired or replaced; 7, should comply with operating procedures, except for the impact of the hand wheel, Strength operation; 8, gland bolts should be evenly symmetrical tightening, gland and stem clearance is too small, should be appropriate to increase its clearance; Gland and stem clearance is too large, should be replaced. Sealing surface leakage reasons: 1, the sealing surface grinding uneven, can not form close-fitting line; 2, stem and closing parts of the connection at the top center of the heart vacant, not correct or wear; 3, valve stem bending or improper assembly, so that the closure of skew Or not in every; 4, sealing surface material quality improper selection or not according to the condition conditions of the valve. Maintenance methods: 1, according to the conditions of the correct choice of material and type of top gasket; 2, carefully adjusted, smooth operation; 3, should be evenly and symmetrically threaded bolts, torque wrenches should be used when necessary, preload should meet the requirements, Not too big or small Flange and threaded connections should have some pre-tightening clearance; 4, Gasket assembly should meet in every, uniform force, gasket is not allowed to overlap and use double shims; 5, static sealing corrosion, damage to processing , Processing quality is not high, should be repaired, grinding, coloring inspection, so that the static sealing meet the relevant requirements; 6, the installation of gasket should pay attention to clean, sealing surface application of kerosene, gasket should not fall to the ground. Seal leakage at the junction of reasons: 1, ring rolling lax; 2, the sealing ring and the body welding, welding quality is poor; 3, the sealing ring thread, screws, pressure ring loosening; 4, corrosion. Maintenance methods: 1, seal leakage at the leak should be re-injection of adhesive and fixed; 2, the seal should be re-soldered welding welding regain the standard. Surfacing Department should not be repaired when the original welding and surfacing welding; 3, remove the screws, pressure ring cleaning, replacement of damaged parts, grinding seal and connection seat close to the surface, re-assembly. Large damage to the larger parts of corrosion, welding, bonding and other methods can be used to repair; 4, the sealing ring corrosion is connected, available grinding, bonding and other methods of repair, repair can not be replaced when the ring. Closure pieces off causes leakage: 1, poor operation, so that the closure of the stuck or over the top dead center, the connection damage broken; 2, the closure of the connection is not strong, loose and fall off; 3, the choice of connection material is wrong, Corrosion from media and mechanical wear. Maintenance methods: 1, the correct operation, close the valve can not be too much force, open the valve can not exceed the top dead center, the valve fully open, the hand wheel should be reversed a little; 2, the closing member and the stem should be connected firmly, the threaded connection should be Stop parts; 3, the closing piece and the stem connection fasteners should withstand the erosion of the media, and have a certain degree of mechanical strength and wear resistance.