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Several matters needing attention in the installation of gaskets

The gasket is a static sealing part that solves “running, emitting, dripping, and leaking”. Since there are many static sealing structures, according to these static sealing forms, flat gaskets, elliptical gaskets, lens gaskets, cone gaskets, liquid gaskets, O-rings, and various self-sealing gaskets have appeared accordingly. The correct installation of the gasket should be carried out when the flange connection structure or the threaded connection structure, the static sealing surface and the gasket are undoubtedly checked, and the other valve parts are intact.

1. Before installing the gasket, apply a layer of graphite powder or graphite powder blended with oil (or water) on the sealing surface, gasket, thread and bolt and nut rotating parts. The gasket and graphite should be kept clean.

2. The gasket must be installed on the sealing surface to be centered, correct, not to be deflected, not to extend into the valve cavity or rest 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 that the gasket is evenly compressed.

3. Only one piece of gasket is allowed to install, and it is not allowed to install two or more pieces between the sealing surfaces to eliminate the lack of gap between the two sealing surfaces.

4. The oval gasket should be sealed so that the inner and outer rings of the gasket are in contact, and the two ends of the gasket should not be in contact with the bottom of the groove.

5. For the installation of O-rings, except that the ring and groove should meet the design requirements, the amount of compression should be appropriate. The flatness of metal hollow O-rings is generally 10% to 40%. The compression deformation rate of rubber O-rings is cylindrical. The static sealing on the upper part is 13%-20%; the static sealing surface is 15%-25%. For high internal pressure, the compression deformation should be higher when using vacuum. Under the premise of ensuring sealing, the smaller the compression deformation rate, the better, which can extend the life of the O-ring.

6. The valve should be in the open position before the gasket is placed on the cover, so as not to affect the installation and damage the valve. When closing the cover, align the position, and do not contact the gasket by pushing or pulling to avoid displacement and scratches of the gasket. When adjusting the position of the cover, you should lift the cover slowly, and then align it gently.

7. The installation of bolted or threaded gaskets should be such that the gaskets are in a horizontal position (the gasket cover for threaded connections should not use pipe wrenches if there is a wrench position). The screw tightening should adopt a symmetrical, alternate, and even operation method, and the bolts should be fully buckled, neat and not loose.

8. Before the gasket is compressed, the pressure, temperature, properties of the medium, and gasket material characteristics should be clearly understood to determine the pre-tightening force. The pre-tightening force should be reduced as much as possible under the condition that the pressure test does not leak (excessive pre-tightening force will easily damage the gasket and make the gasket lose its resilience).

9. After the gasket is tightened, it should be ensured that there is a pre-tightening gap for the connecting piece, so that there is room for pre-tightening when the gasket leaks.

10. When working at high temperatures, the bolts will experience high temperature creep, stress relaxation, and increased deformation, leading to leakage at the gasket and requiring thermal tightening. On the contrary, under low temperature conditions, the bolts will shrink and need to be cold loosened. Hot tightening is pressurization, cold loosening is pressure relief, hot tightening and cold loosening should be performed after maintaining the working temperature for 24 hours.

11. When a liquid gasket is used for the sealing surface, the sealing surface should be cleaned or surface treated. The flat sealing surface should be consistent after grinding, and the adhesive should be evenly applied (the adhesive should be compatible with the working conditions), and air should be excluded as much as possible. The adhesive layer is generally 0.1 ~ 0.2mm. The screw thread is the same as the flat sealing surface. Both contact surfaces must be coated. When screwing in, it should be in a vertical position to facilitate air discharge. The glue should not be too much to avoid spilling and staining other valves.

12. When using PTFE film tape for thread sealing, the starting point of the film should be stretched thin and glued to the thread surface; then the excess tape at the starting point should be removed to make the film sticking to the thread into a wedge shape. Depending on the thread gap, it is generally wound 1 to 3 times. The winding direction should follow the screwing direction, and the end point should be coincident with the starting point; slowly pull the film into a wedge shape, so that the thickness of the film is evenly wound. Before screwing in, press the film at the end of the thread so that the film can be screwed into the internal thread together with the screw; the screwing should be slow and the force should be even; do not move again after tightening, and avoid turning, otherwise it will be easy to leak.