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
- 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.
- Attrition : (Figure 2) 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.
- By Heat, such as in the case of seating 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 tamped 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.
In general, it is considered that only the gasket
surface provides the seal in the joint. It is assumed that the gasket
material is impervious and will not permit any passage of fluid
through the gasket seal.