Reference Manual

1−11
Figure 1-21. Comprehensive Packing Material Arrangements
for Globe-Style Valve Bodies
B2565
Figure 1-19. Mechanically Formed Bellows
A5954
Figure 1-20. Welded Leaf Bellows
A5955
The mechanically formed bellows is taller in
comparison and is produced with a more
repeatable manufacturing process.
Control Valve Packing
Most control valves use packing boxes with the
packing retained and adjusted by a flange and
stud bolts (figure 1-27). Several packing materials
can be used depending upon the service
conditions expected and whether the application
requires compliance to environmental regulations.
Brief descriptions and service condition guidelines
for several popular materials and typical packing
material arrangements are shown in figure 1-21.
PTFE V-Ring
D Plastic material with inherent ability to
minimize friction.
D Molded in V-shaped rings that are spring
loaded and self-adjusting in the packing box.
Packing lubrication not required.
D Resistant to most known chemicals except
molten alkali metals.
D Requires extremely smooth (2 to 4
micro-inches RMS) stem finish to seal properly.
Will leak if stem or packing surface is damaged.
D Recommended temperature limits: −40°F to
+450°F (−40°C to +232°C)
D Not suitable for nuclear service because
PTFE is easily destroyed by radiation.