How a compression packing is braided will determine how the packing installs and performs. Specifically, the way the packing is braided will affect how it responds to such factors as gland load, internal pressure, shaft speed, and media properties and characteristics.
About Braided Packing
Braided packing is usually manufactured with a square or rectangular cross-section, and is made from a range of different materials, including aramid fibres, PTFE, graphite and flexible graphite, and others. Compression packing can thus vary in terms of both the material from which it is made and the way the material is braided to form the packing.
The way in which a packing is braided will determine its radial expansion. Braid types, such as a lattice braid which are more tightly woven, will tend to have a lower radial expansion. This type of packing may be better suited to applications in which the equipment being packed is newer and at an earlier stage in its life cycle.
As equipment moves through its life cycle and ages, wear and tear results in looser tolerances and “slop”. For such older equipment, selecting a more loosely braided packing, such as one with a square braid, may provide superior performance and service.
Packing which features tighter braiding will tend to be less flexible, and may therefore be harder to install on some equipment. Thus, when choosing packing, ease of installation may be another factor to consider.
Braided Packing: Construction Types
The following are the braid construction types commonly found on most commercially available compression packing:
Twisted braid
Square braid
Lattice braid (sometimes called interlock or interbraid)
Braid over core
Braid over braid
Twisted fibre packing is usually made from cotton fibres twisted and impregnated with mineral oil and graphite. While a common type of packing, twisted fibre packing is not as strong as packing which features interlocked braids. It is therefore better suited to lighter applications.
Square braid packing is a commonly used packing whose relatively loose weave permits a higher radial expansion than other braid types. This characteristic is particularly useful when packing pumps that have seen long service and may have worn stuffing boxes and shaft sleeves. Square braid packing will often work in applications where a more tightly woven packing will not expand sufficiently to achieve a good seal.
In contrast, lattice braid packing has a tighter weave and may be a better choice when servicing newer equipment. The tighter weave of this packing provides fewer leak paths through which media can travel. The interlocking nature of the braid makes it resistant to unravelling and fraying.
Braid over core type is often found on valve packing. The core of the packing may consist of either extruded rubber or tightly braided material. This core is then overlain with another braid that may contain wire to mitigate the effects of the high pressures often found in valves. The rubber core used in this packing adds resiliency and allows the packing to recover to its original configuration when compressive load is relieved.
Braid over braid type packing usually consists of a circular cross-section, sometimes with a center composed of wire strands for added strength. This core is then overlain with several layers of braided material, which may be impregnated with lubricants.
Teadit Compression Packing from CRGI
CRGI carries a full line of quality compression packing produced by Teadit North America and available in a range of styles and constructions that suit a wide range of applications. Packing styles that we carry include the following:
Carbon fiber and graphite
Expanded PTFE
Synthetic yarn
Aramid yarn
ePTFE/Graphite
Ramie
If you have a compression packing need, our sales specialists will be pleased to speak with you to determine your application requirements.
To find out more about any of the compression packing we can supply, please contact our sales department at crg@canadarubbergroup.com.