term "pneumatic seals" actually describes a class of
seals that are used in applications with either rotary or reciprocating
motions. Pneumatic seals are exposed to air with a minimum amount
of lubrication. They are often used in pneumatic cylinders and
valves and usually are not under high pressure. However, pneumatic
seals may be exposed to high operating speeds.
seals, piston seals, u-cups, vee-cups and flange packings are
just some of the sealing designs that can be used for a pneumatic
seal. Sometimes a composite seal is used as a pneumatic seal.
A composite seal is a product which has two or three materials
manufactured into one seal. Often there will be an elastomer ring
and a PTFE ring giving the seal the advantages of both materials.
sealing orientation for pneumatic seals can include internal (rod
seal), external (piston seal), symmetrical or axial seal. With
the internal (rod) seal, the seal is fit into a housing bore and
the sealing lip touches the shaft. With the external (piston)
seal, the seal is placed onto a shaft and the sealing lip touches
the housing bore. Since symmetric seals are the same on both sides
they will function as either a rod or a piston seal. The axial
seal fits axially against the housing.
applications need only one pneumatic seal (single acting) because
it can seal in the one axial direction the application is moving.
However, a reciprocating application will need two pneumatic seals
(double acting) one for each of the directions.