Body and bonnet leakage reasons: 1, the cast iron casting quality is not high, there are sand holes on the body and bonnet, loosely organized, defects such as slag; 2, day frozen crack; 3, poor welding, there is a slag, no welding, stress crack defects such as; 4 after being hit by heavy, cast iron valve damage. Maintenance methods: 1, improve the quality of casting, before installation in accordance with the provisions of strength test; 2, the temperature is below 0 ℃ and 0 ℃ of valve, should be insulated or hot, stop using the valve should be ruled out water; 3, composed of the body and cover welding seam, should according to the relevant welding procedures, also should carry on the inspection and after welding strength test; 4, the valve prohibited put heavy, do not allow the hammer impact non-metallic valves, cast iron and the installation of large diameter valves should be stand. Packing of the leakage of Industrial Valves leakage, packing for the largest percentage. Reason: 1, selection of packing is wrong, no resistance to corrosion medium, not resistant to high pressure or vacuum valve, the use of high and low temperatures; 2, packing installation is wrong, there is a generation with a little one for a big, spiral wound joints, tighten the loose defects such as; 3, packing more than life, have aging, loss of elasticity; 4, the valve stem precision is not high, has defects such as bending, corrosion, wear and tear; 5, packing ring, gland not compaction; 6, gland, bolts, and other components damaged, make gland cannot compress; 7, improper operation, too hard, etc. ; 8, gland skew, gland and the gap between the stem is too small or too large, the valve stem wear and damage of the packing. Maintenance methods: 1, should according to the working condition choose packing materials and type; 2, according to the relevant provisions of the correct installation packing, packing should be by circle put pressure, joint should be 45 ℃ to 30 ℃ or; 3, life is too long, aging, damage of packing should be replaced in a timely manner; 4, the stem should be into straightening after bending, wear, repair, the badly damaged should be replaced in a timely manner; 5, packing shall be installed in a specified number of turns and gland should be symmetrical evenly the tight, pressing sleeve should be preloaded gap more than 5 mm; 6, the damaged gland, bolts and other components, should be timely repair or replacement; 7, shall comply with the operational procedures, in addition to the percussive handwheel, normal force at a constant speed operation; 8, should be symmetrical tighten gland bolts evenly, gland and the gap is too small, the stem should be appropriate increase its clearance. Gland and stem gap is too big, should be replaced. The leakage of sealing surface reasons: 1, the sealing surface grinding, cannot form a closed line; 2, the valve stem and shut down a joint centers are suspended, incorrect or wear; 3, the valve stem bending or assembly is not straight, make close a skewed or do not meet; 4, the sealing surface material selection of quality or not according to the working condition valve. Correct maintenance methods: 1, according to the working condition choose top gasket materials and type; 2, the careful adjustment, stable operation; 3, should be symmetrically screw bolt, torque wrenches should be used when necessary, should comply with the requirements, the prestressing force is too large or small. Flange and threaded joints due and certain preloaded gap; 4, gaskets for assembly should meet, force uniform, gaskets are not allowed to overlap and the use of double gasket; 5, the static sealing surface corrosion and damage to processing, processing quality is not high, should be repaired, grinding, the examination of the color, make the static sealing surface in compliance; 6, installing a spacer should pay attention to clean and sealing surface application of kerosene, gaskets should not fall to the ground. Sealing ring link leak reason: 1, the sealing ring rolling is lax; 2, sealing and ontology welding, welding quality is poor; 3, sealing ring connection loose thread, screw, compression ring; 4, sealing ring connected by corrosion. Maintenance methods: 1, sealed rolling place leak should note adhesive rolling fixed again; 2, the sealing ring should be according to the welding specification to don't understand the repair welding of shi. When unable to repair welding should be cleared the original welding and surfacing processing; 3, remove screw, pressure washing, replacement of damaged parts, grinding seal and connection closed surface, repackaging. Of corrosion damage larger components, available methods of welding, bonding repair; 4, sealing ring junction surface corrosion, usable abrasive, adhesive and other methods to repair, should replace the sealing ring are used when beyond repair. Shut off leakage causes: 1, the operation is bad, make close a jammed or over top dead center, joint damage fracture; 2, close the connection is not strong, slacken off and fall off; 3, choose fitting material is wrong, can't afford to medium corrosion and mechanical wear and tear. Maintenance methods: 1, the correct operation, close the valve don't too hard, open valve cannot exceed top dead center, after the Industrial Valves fully open, the handwheel should reverse a little; 2, close connected to the stem should be solid, threaded joints should be check the product; 3, closed connected to the Industrial Valves stem with fasteners should withstand the corrosion of medium, and has certain mechanical strength and wear resistance.
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