Compression packing seals are part of the oldest and most common sealing process, compression packing. In compression packing, sealing is accomplished by tightening a gland along the top ring of the stuffing box so that the packing is compressed onto the surface to be sealed. Compression packing seals, or gland seals, include the following: compression packing, gaskets, mechanical seals, gasket material, and other fluid sealing devices. Compression packing seals can seal a number of fluids including water, acids, solvents, gases, oil, and other chemicals in a range of conditions based on temperature and pressure. “Compression packing seals” is a broad category that covers seals that are manufactured in a wide array of shapes, sizes, and constructions from many materials.
Before selecting compression packing materials, it is important to understand a number of specific parameters that can effect performance: the size of the cross section that is to be sealed, the media and its specific qualities, the type of equipment (i.e., pumps, valves, mixers, etc.), the temperature and pressure of the media being sealed, and shaft or rubbing speed if the machinery is a pump or rotates. Once these variables have been determined the proper compression packing seals can be selected.
There are several compression packing seals to choose from when packing, these seals are: braid-over-braid; braid-over-core; laminated; multi-braid / lattice; plaited / square-braid; twisted; and wrapped, rolled and folded.
Braid-over-braid construction, also referred to as jacket-over-jacket, is created by braiding one or more strands over a center core of braided, twisted, or homogeneous materials. This design can be braided round and then made square. The weave of the braid is soft and dense because of individual jacket-over-jacket construction which carries a high amount of lubricant.
The braid-over-core design is produced by round braiding one or more jackets of yarn, rovings, ribbons, or other forms of materials over a core. These materials maybe extruded, twisted, wrapped or knitted.
Laminated compression packing seals are formed from asbestos and rubber mixture, or a mix of duck and rubber, which are laminated into slab form. Once laminated into a slab they are fabricated into spirals, coils, or rings.
In multi-braid, or lattice seals, strands are diagonally braided for increased stability and longevity. Each strand passes diagonally and crisscrosses through the body of the packing at an angle of approximately 45°. This crisscrossing allows the stands to be locked into a solid structure that is not easily unraveled. The multi-braid design is resistant to permeation leakage and would not be entirely damaged even if the surface were to get worn.
Plaited seals, sometimes referred to as square-braided seals, are constructed from interwoven yarns with pockets between each plait to retain lubricant. These interwoven yarns have a square cross-section structure which is soft, absorbent, and can carry a high amount of lubricant. The plaited / square-braid design is especially suited for high-speed rotary service, particularly at low pressure.
Twisted compression packing seals are a simple design. Yarns or metallic strands are twisted together to obtain the desired size. One packing size can be used for numerous stuffing boxes. Twisted seals are primarily a general or emergency type of packing where packing space is small.
Wrapped, rolled and folded compression packing seals use strips of various forms of materials (metals, rubberized fabrics, etc.). These seals are spirally wrapped, rolled, or folded upon itself or around a compressible core. The metallic types have the ability to conform to the inconsistencies of used or worn equipment. The rubberized fabric types are strong, dense, and flexible. However, both types can be made resistant to the absorption of fluids.
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