Valve flange sealing connection between contact parts according to design requirements put sealing gasket, rely on the connection bolt pre-tightening force generated by the enough pressure, prevent leakage of medium to the outside. Gasket materials and structures are: rubber gasket, asbestos rubber gasket, graphite gaskets, stainless steel and graphite spiral wound gasket, corrugated tube and metal gasket. Gasket seal belongs to forced sealing. Common flange leak has the following kinds: a. Interface between leak sealing gasket and flange end face and untight seal leakage. Main reason: not enough sealing gasket pre-tightening force - processing method: appropriate increase pre-tightening force. Did not comply with the flange sealing surface roughness requirements, processing methods: repair; Flange surface uneven or lateral has scratches - processing method: repair; Cold and hot deformation and mechanical vibration etc - processing method: improve the environment or material selection; Flange connection bolt deformation and elongation, processing methods: materials and cannot exceed allowable torque; Sealing gasket long-term use of plastic deformation occurred - processing method: replacement; Sealing gasket aging, cracking and metamorphic - processing method: replacement. b。 Penetration leak - medium under the action of pressure, leak through the gasket material gap. The main reason: associated with sealing gasket materials; The pressure of medium; The temperature of the medium. Sealing gasket aging, cracking and metamorphism. c。 Leak - the result of the installation quality lack of excessive compression or sealing gasket sealing pressure and leakage. Main reason: sealing gasket installation deflection, make local sealing pressure is insufficient or pre-tightening force is too large, losing the ability to rebound; Flange connection bolt tightness is not uniform; Two flange alignment ( Deviation from the center line) Deflection; Sealing gasket to choose correct choose wrong or not according to the working condition of gasket materials and type; Interface leakage and leakage will significantly increase as time goes on, on the relationship between the infiltration leakage and leakage time is not obvious. ( Reprint, please indicate the source)