Packing seal structure and principle

2021.11.10 170次

Commonly used packing seals compress the packing on the surface of the shaft through the packing gland. Since the surface of the shaft is always somewhat rough, it can only partially fit with the filler, while the part is not in contact, thus forming countless labyrinths. When the pressurized medium passes through the shaft surface, the medium is throttled many times, and the seal is achieved by virtue of this "labyrinth effect". The adhesion and friction between the packing and the shaft surface are also similar to sliding bearings, and there should be enough liquid for lubrication to ensure a certain life of the seal, which is the so-called "bearing effect". It can be seen that a good packing seal is a combination of the labyrinth effect and the bearing effect.


         The compression force of the packing on the shaft is produced by tightening the gland bolts. Since the packing is an elastoplastic body, when it is compressed in the axial direction, the friction force is generated and the compression force is gradually reduced in the axial direction. At the same time, the radial compression force generated makes the packing close to the shaft surface to prevent the medium from leaking. From the outer end (gland) to the inner end, it decreases sharply at first and then gradually decreases from the inner end to the outer end. When the medium pressure at the outer end is zero, there is little leakage, and when it is greater than zero, the leakage is greater.