The gasket of sealing material is a static sealing part to solve the problem of "running, emitting, dripping and leaking". Because there are many kinds of static sealing structure, according to these static sealing forms, there are corresponding flat gasket, elliptical gasket, lens gasket, conical surface gasket, liquid sealing gasket, O-ring and various self sealing gaskets.
The correct installation of the gasket should be carried out under the condition that the flange connection structure or thread connection structure, static sealing surface and gasket are doubtless inspected, and other valve parts are intact.
Before installing the gasket, the sealing surface, gasket, thread and the rotating part of the bolt and nut shall be coated with a layer of graphite powder or a lubricating agent mixed with oil (or water), and the gasket and graphite shall be kept clean.
The gasket installed on the sealing surface should be in the middle and correct. It should not be skewed or extended into the valve chamber or placed on the shoulder. The inner diameter of the gasket should be larger than the inner hole of the sealing surface, and the outer diameter should be slightly smaller than the outer diameter of the sealing surface, so as to ensure the uniform compression of the gasket.
Only one gasket is allowed to be installed, and two or more pieces are not allowed to be installed between the sealing surfaces to eliminate the insufficient gap between the two sealing faces.
The sealing of elliptical gasket shall make the inner and outer rings of the gasket contact each other, and the two ends of the gasket shall not contact with the groove bottom.
For the installation of O-ring, in addition to the ring and groove should meet the design requirements, the compression amount should be appropriate. The general flattening degree of metal hollow O-ring is 10% ~ 40%, the compression deformation rate of rubber O-ring is 13% ~ 20% for the static seal on the cylindrical surface and 15% ~ 25% for the plane static sealing surface. For high internal pressure, the compression deformation should be higher in vacuum. On the premise of ensuring the sealing, the smaller the compression deformation rate is, the better, and the service life of O-ring can be prolonged.
Before the gasket is on the upper cover, the valve should be in the open position to avoid affecting the installation and damaging the valve parts. The cover should be aligned with the position. It is not allowed to contact the gasket by pushing and pulling, so as to avoid displacement and scratch of the gasket. When adjusting the position of the cover, the cover should be slowly lifted up, and then gently put down in alignment.
The gasket with bolt connection or threaded connection shall be installed in a horizontal position (for screw connected gasket cover, pipe wrench shall not be used if there is wrench position). The screw thread shall be tightened symmetrically, alternately and evenly, and the bolts shall be fully buckled, neat and free of looseness.
Before the gasket is pressed, the pressure, temperature, medium properties and gasket material properties should be understood clearly to determine the preload. The preload should be reduced as much as possible without leakage during pressure test (excessive preload will easily damage the gasket and cause the gasket to lose resilience).
After the gasket is tightened, it is necessary to ensure that there is a pre tightening gap between the connecting pieces, so as to have room for pre tightening in case of gasket leakage.
When working at high temperature, the bolt will produce high temperature creep, stress relaxation and deformation increase, which will lead to leakage of gasket and need hot tightening. On the contrary, under low temperature conditions, the bolt will shrink and need cold loosening. Hot tightening means pressurization and cold loosening is pressure relief. Hot tightening and cold loosening should be carried out after maintaining the working temperature for 24h.