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Pneumatic Cylinder Seal Selection: Types, Materials, Dimensions, and Quotation Data
Quick Answer: A pneumatic cylinder seal keeps compressed air inside the cylinder and keeps contamination outside the rod and piston area. Select the seal by bore diameter, rod diameter, groove dimensions, material, pressure, temperature, cycle speed, and lubrication condition. CORASEALS supplies pneumatic cylinder seals, wear rings, wiper seals, and pneumatic cylinder seal kits based on measured dimensions and operating data.
Pneumatic cylinder seals are used in air cylinders for factory automation, packaging, valve actuation, clamping, pressing, and other compressed air applications. The seal profile must match the groove shape and the direction of air pressure. A seal that works well in a hydraulic cylinder may not be the best choice for a pneumatic cylinder because air has lower lubricating film strength than hydraulic oil.
Most pneumatic cylinders work at lower pressure than hydraulic cylinders. However, many pneumatic cylinders run at high cycle rates and must keep friction low. The rod surface, cylinder bore finish, air quality, and lubrication all affect seal life. If one condition changes, the seal material or profile may need to change.
Pneumatic Cylinder Seal Positions
Different positions in a pneumatic cylinder require different seal functions. The main positions are listed below.
- Piston seal: Seals the gap between the piston outside diameter and the cylinder bore.
- Rod seal: Seals the gap between the cylinder head and the moving rod.
- Wiper seal: Removes dust, moisture, and particles from the rod surface before the rod enters the cylinder head.
- Wear ring: Guides the piston or rod and prevents metal to metal contact under side load.
- Static O-ring: Seals end caps, cushion sleeves, and other fixed joints.
- Cushion seal: Controls air flow at the end of stroke in cylinders with cushioning features.
A full repair set is often sold as a pneumatic cylinder seal kit. The kit normally includes piston seals, rod seals, wiper seals, static O-rings, wear rings, and cushion seals. The exact kit contents depend on the cylinder design and the original manufacturer.
Common Pneumatic Cylinder Seal Profiles
The common profiles for pneumatic cylinder seals are O-rings, U-cups, lip seals, compact seals, wiper profiles, and wear rings. Each profile has a different sealing mechanism.
| Seal Profile | Typical Position | Main Function |
|---|---|---|
| O-ring | Piston OD or static joint | Low cost sealing for light duty and static applications |
| U-cup | Piston OD or rod ID | Single acting lip seal with moderate friction and good air retention |
| Compact seal | Piston or rod | Multi piece seal for limited groove space and lower friction |
| Wiper seal | Rod entry | Removes contamination from the rod surface |
| Wear ring | Piston or rod | Guides the moving part and prevents metal contact |
| Cushion seal | Cushion area | Controls end of stroke air flow and reduces impact |
Do not order by profile code alone. Codes such as UN, UHS, D-9, or KDAS can differ between seal catalogs. Always confirm the cross section drawing, material, and dimensions before replacing a pneumatic cylinder seal.
Material Selection for Pneumatic Cylinder Seals
Material selection depends on air temperature, air quality, compressor oil, grease, and whether the cylinder operates wet or dry. NBR and polyurethane are common f