Why does the octagonal pad need to be tightened again? Can’t use fixed torque either?

Fixed torque is a method, but the resulting pulling force may not be sufficient, and it could exert excessive force on the bolt, causing it to break. Due to the thin thickness of the octagonal washer, it is not possible to achieve sufficient tension with a single tightening, so a two-step tightening process must be used. After two tightening steps, the pulling force on the octagonal washer can be gradually increased from different directions until it reaches the force required by the design, thereby ensuring the tightness of the bolt. -

Octagonal gaskets usually require secondary tightening, as wear and deformation during use can cause the gasket to lose some of its tightening force, thereby affecting its sealing performance. Therefore, in some applications where high sealing performance is required, the octagonal gasket needs to be tightened again to ensure it fits tightly against the sealing surface. Constant torque can also be used to control the tightening force, but it can only ensure a certain level of tightening force and cannot accurately control its magnitude. Furthermore, a fixed torque cannot respond promptly to or adjust for issues such as deformation and loosening of the octagonal gasket, thus secondary tightening is required. It is worth noting that secondary tightening should be carried out promptly after loosening; excessive tightening force can also cause problems such as deformation or cracking of the gasket, so it is necessary to know the appropriate amount of tightening force.

A regular octagonal washer usually only requires one torque application; those that need to be tightened twice are probably the elliptical washers