Application Information And Sealing Arrangements

Materials of Construction Basically, stuffing box packing is a pressure breakdown device. In order for a packed stuffing box to operate properly, the correct packing must be

FIGURE 4 Graphite acrylic packing in FIGURE 5 Non-asbestos packing (John Crane Inc.)

continuous form (John Crane Inc.)

FIGURE 6 Flexible graphite packing rings (John Crane, Inc.)

applied and the appropriate design features must be included in the system. Numerous types of packing materials are available, each is suited to a particular service. These may be grouped into three categories:

1. Non-asbestos packing Since asbestos is no longer available as a packing material, other types of packing material are being used. These include cotton, TFE filament, Aramid fiber, aromatic polyamides, graphite/carbon yarn, and flexible graphite. All of these materials, with the exception of flexible graphite, can be impregnated with various lubricants. An example of graphited acrylic packing is shown in Figure 4. With the exception of flexible graphite, all the materials are of an interlaced construction for greater flexibility (see Figure 5). Packing made with this type of construction remains intact even if individual yarns wear away at the inside diameter of the packing.

2. Flexible graphite These types of packing rings were originally available cut from laminated sheet stock that required the rings to be made with an interference fit. Flexible graphite rings are made today from ribbon tape that is easily compressed to the shaft and bore to affect a better seal. Flexible graphite rings are available in split or endless rings (see Figure 6) or as the ribbon tape itself for ease of maintenance and installation. Operating limits for non-asbestos packings are found in Table 6.

3. Metallic packing The basic materials of construction are lead or babbit, aluminum, and copper in either wire or foil form. Metallic packing rings have flexible cores of non-asbestos materials such as twisted glass fiber. The packing is impregnated with graphite grease and/or oil lubricants (see Figures 7 and 8). Babbit is used in water and oil services at temperatures up to 450°F (229°C) and pressures up to 250 lb/in2 (17 bar). Copper foil is used with water and low sulfur oils. Aluminum

TABLE 6 Service limitations of common packing materialsa

Packing Material

Pressure (max.)b lb/in2 gage (bar)

PV rating (max.)6 lb/in2 gage • fpm (bar • m/s)

Temp.

(max)d °F (°C)

pH Range

Comments

Cotton

100 (6.8)

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