Page 289 - The Tribology Handbook

B25 Packed glands

PACKING MATERIALS
Table 25.1 Materials for use in packed glands

Maximum operating
Material Special properties Typical application5
temperature “C
Expanded graphite foil 550°C Low friction, self lubrication, Valve stems
2500°C in non-oxidising low compression set and
environments contains no volatile
constituents. Available as
rings
Graphite/yarn filament 550°C Available as cross plaited Valve stems
square section lengths.
Resistant to extrusion
Aramid (Kevlar) fibre 250°C Tough and abrasion resistant Valve stems and pumps
PTFE filament 250°C Low friction and good Valve stems
chemical resistance Pumps at surface speeds below
10 m/s

Hybrid graphite/PTFE yarn 250°C Particularly suitable for high Pump shafts for speeds of the
speed rotary shafts. order of 25 m/s
Close bush clearances needed
to reduce risk of extrusion.
Good resistance to abrasives.
__
~~~ ~
Ramie 120°C Good water resistance Rotary and reciprocating
water pumps
Note: Many of these packings can be provided with a central rubber core which can increase their elasticity and thus assist in
maintaining the gland compression. Their application depends on the temperature and chemical resistance of the type of rubber used.

PACKING DIMENSIONS AND FITTING

Typical gland dimensions are shown in Figure 25.1 1 and packing sizes in Table 25.2.
Table 25.2 Typical radial housing widths in relation to shaft diameters. All dimensions in mm

All packings except expanded graphite Exponded graphite
Shajl diameter Housing radial width Shaft diameter Housing radial width
up to 12 3 up to 18 3
above 12 to 18 5 above 18 to 75 5
18 to 25 6.5 75 to 150 7.5
25 to 50 8 150 and above 10
50 to 90 10
90 to 150 12.5
150 15

825.3