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Working Principle Of Gland Packing Seal

The packing is installed in the stuffing box, and the packing is pressed on the surface of the shaft through the packing gland. Because the surface of the shaft is always rough, it can only partially fit with the packing, and the part does not touch, thus forming countless labyrinths. When the pressurized medium passes through the shaft surface, the medium is throttled for many times, and the seal is achieved by virtue of this "labyrinth effect". The fit and friction between the packing and the shaft surface is also similar to the sliding bearing, and there should be enough liquid for lubrication to ensure that the seal has a certain life, which is the so-called "bearing effect". It can be seen that a good packing seal is the combination of labyrinth effect and bearing effect.
The compression force of the packing on the shaft is generated by tightening the gland bolts. Because the packing is an elastoplastic body, when it is compressed axially, the friction force will gradually reduce the compression force along the axial direction. At the same time, the radial compression force will make the packing close to the surface of the shaft and prevent the leakage of the medium. The distribution of radial compression force decreases sharply from the outer end (gland) to the inner end and then becomes flat. The distribution of medium pressure decreases gradually 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, there is leakage.
With the continuous emergence of new materials, the structural type of packing has also changed a lot, which will undoubtedly promote the application of packing seals more widely. The materials used as packing should have the following characteristics: certain elastoplasticity. When the packing is compressed axially, it can produce a large radial compression force to obtain a seal; When the machine and shaft have vibration or the shaft has runout and eccentricity, it can have certain compensation ability (tracking); Chemical stability. It will not be corroded, dissolved or polluted by the medium; Impermeability. The medium has some penetration to most fibers, so the filler organization is required to be compact. Therefore, it is often necessary to impregnate and fill various lubricants and fillers when making the filler; Good self-lubrication, low friction coefficient and wear resistance; Temperature resistance. It can bear a certain temperature after friction heating; Easy disassembly; Simple manufacturing and low price.
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Alex Zhang