Tip: Pneumatic Seals

The 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.

Rod 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.

The 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.

Rotary 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.