Gaskets,
Packings and Seals
A gasket
is a material that is used to seal two faces of a machine.
Gaskets can be made of a soft materials, such as asbestos or
elastomers, or they can be made of harder materials, such as metal
ring gaskets made of iron, steel and other materials. Combinations of
materials such as spiral-wound metal/asbestos-filled gaskets
are also common.
Gaskets
are designed for compressibility and sealability. Compressibility is
a measure of the gasket's ability to deflect and conform to
the faces being sealed. Gaskets compressibility compensates
for surface irregularities, such as minor nicks, non-parallelism,
corrosion and variations in groove depth. Sealability is the measure
of fluid leakage through and across both faces of a gasket.
Most of the leakage for a properly installed face to face connections
will occur through the gasket.
Types
of Gaskets
Gaskets
are classified usually either by the material from which they are
made and the type of construction or design or in some cases both.
Flat
Gasket
Flat
gaskets are cut from flat stock of gasket material. The
material can be elastomer, either natural ( rubber ) or synthetic (
hypalon, viton, SBR ). Fiber material is often formed with a binder
into flat stock gasket material. Flat stock comes in standard
thickness ranging from 1/64” to 1/4”. Flat stock gaskets
are often cut into full face gaskets, in which the gasket
design incorporates the appropriate bolt-hold pattern and the flange
bolts are used to center the gasket in place. The full face
design is most often used with the flat face flange design. Ring face
gaskets are cut so that the outer diameter of the gasket
rest inside the bolt pattern and the gasket is centered by
resting it on the flange bolts.
Envelope
Gasket
Envelope
gaskets consist of an elastomeric material protected by
another material as a gasket. TFE is common envelope material
because of its resistance to many chemicals. Envelope gaskets
are usually ring face sized so that the gasket is centered by
resting on the flange bolts. Different metals can be used as the
envelope material.
