packing makes it unsatisfactory for modem, high-
The centering ring is used as a reinforcement to
temperature, high-pressure equipment. Two types
prevent blowouts. The filler piece is replaceable.
of gaskets (metallic or semimetallic) are in use in
When renewing a gasket, you should remove this
present day high-temperature and high-pressure
piece from the retaining metal ring and replace
it with a new filler. Do not discard the solid metal
installations. Gaskets of corrugated copper or of
asbestos and copper are sometimes used on low-
retaining outer or centering ring unless it is
and medium-pressure lines.
damaged. You can compress the gaskets to the
thickness of the outer or centering ring.
Serrated-face metal gaskets (view B of fig.
When renewing a gasket in a flange joint, you
6-50) made of steel, Monel, or soft iron have
must exercise special precautions when breaking
raised serrations to make a better seal at the
piping flange joints. These gaskets have resiliency.
the joint, particularly in steam and hot water lines,
Line pressure forces the serrated faces tighter
or in saltwater lines that have a possibility of direct
connection with the sea. Be sure to observe the
against the adjoining flange. The gaskets shown
following precautions:
are of two variations.
Spiral-wound, metallic-asbestos gaskets (view
C of fig. 6-50) are made of interlocked strands
1. No pressure is on the line.
of preformed corrugated metal and asbestos
2. The line pressure valves, including the
strips, spirally wound together (normally called
bypass valves, are firmly secured, wired
the FILLER), and a solid metal outer or centering
closed, and tagged.
3. The line is completely drained.
ring (normally called the RETAINING RING).
4. At least two flange-securing bolts and nuts
diametrically opposite remain in place
until the others are removed, then
slackened to allow breaking of the joint,
and removed after the line is clear.
5. Precautions are taken to prevent explosions
or fire when breaking joints of flammable
liquid lines.
6. Proper ventilation is ensured before joints
are broken in closed compartments.
These precautions may prevent serious
explosions, severe scalding of personnel, or
f l o o d i n g of compartments. You should
thoroughly clean all sealing and bearing surfaces
for the gasket replacement. Check the gasket seats
with a surface plate, and scrape as necessary. This
affords uniform contact. Replace all damaged
bolt studs and nuts. In flange joints with raised
faces, the edges of gaskets may extend beyond the
edge of the raised face.
O-RINGS
Another method of preventing leakage in fluid
systems is by use of O-ring seals. Figure 6-51
shows an O-ring seal with two cross-sectional
views. An O-ring is a doughnut-shaped, circular
seal (view A of fig. 6-5 1) that is usually a molded
rubber compound. An O-ring seal has an O-ring
mounted in a groove or cavity (usually called a
gland).
When the gland is assembled (view B of fig.
6-51), the O-ring cross section is compressed.
When installed, the compression of the O-ring
Figure 6-51.--O-ring seal with two cross-sectional views.
6-36
