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Effecting a Seal
 A
seal is affected by compressing the gasket material
and causing it to flow into the imperfections on the
gasket seating surfaces so that intimate contact is
made between the gasket and the gasket seating
surfaces preventing the escape of the confined
fluid. Basically there are four different methods
that may be used either singly or in combination to
achieve this unbroken barrier.
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Compression (Figure 1 ). This is by far the most
common method of effecting a seal on a flange
joint and the compression force is normally
applied by bolting.
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Attrition (Figure 2). Attrition is a combination
of a dragging action combined with compression
such as in a spark plug gasket where the spark
plug is turned down on a gasket that is both
compressed and screwed into the flange.
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By heat, such as in the case of sealing a bell
and spigot joint on cast iron pipe by means of
molten lead. Note, however, that after the
molten lead is poured, it is tampered into place
using a tamping tool and a hammer.
Gasket
lip expansion. This is a phenomenon that would occur
due to edge swelling when the gasket would be
affected by confined fluid, as in the case of
elastomeric compounds affected by the confined
fluids, such as solvents, causing the gasket
material to swell and increase the interaction of
the gasket against the flange faces.
Generally,
gaskets are called upon to effect a seal across the
faces of contact with the flanges. Permeation of the
media through the body of the gasket is also a
possibility depending on material, confined media,
and acceptable leakage rate.>>The
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