Pneumatic seals are used in rotary or reciprocating motion applications, such as pneumatic cylinders and valves. They require minimal lubrication and can handle high operating speeds but not high pressure. Composite seals made of different materials are often used. Sealing orientation can be internal, external, symmetrical, or axial. Rotating applications require single acting seals, while double acting seals are needed for alternative applications.
Pneumatic seals are one of a class of seals used in applications that include rotary or reciprocating motion. They are often used in pneumatic cylinders and valves, but do not perform well under high pressure.
This type of seal requires minimal lubrication when exposed to air to create an airtight seal. Pneumatic seals can also be exposed to high operating speeds where the pressure is not high. Piston seals, rod seals, flange seals, U-cups, and Vee-cups are a few such designs. The difference between pneumatic and hydraulic seals is pressure. Pneumatic seals typically have a pressure range of 1 to 150 pounds of force per square inch (psi) (about 6.89 to 1,034.2 kilopascals), while hydraulic pressure can reach more than 10,000 psi (68.9 megapascals).
Sometimes, composite seals, made up of two or three different materials, are used as pneumatic seals. They are therefore often found in products that require a seal for many parts. In this situation, a PTFE ring and an elastomer ring are often used. NASA uses this technology in its rocket systems. Composite air seals are also used in truck diesel engines.
The sealing orientation of a pneumatic seal can be internal, such as with a rod seal; external, as with a piston; symmetrical; or axial. With internal seals, a housing bore surrounds the seal and the sealing lip contacts the shaft. This type requires very little lubricant.
With pneumatic outer piston seals, the seal surrounds a shaft and the lip contacts the bore of the housing. This system requires more lubrication. Symmetrical seals are the same on both sides, and axial seals fit axially against the housing. In both cases, however, the seals are used externally and require more lubrication.
Rotating applications require only one pneumatic seal. It is considered single acting because it can seal in one axial direction while the application is in motion. On the other hand, an alternative application requires two seals or double acting seals. In this case, one seal is required for each of the directions. Double-acting seals are more complicated than single-acting ones.
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