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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.
Different positions in a pneumatic cylinder require different seal functions. The main positions are listed below.
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.
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 depends on air temperature, air quality, compressor oil, grease, and whether the cylinder operates wet or dry. NBR and polyurethane are common for standard pneumatic cylinders. FKM and HNBR are selected for higher heat or chemical exposure. PTFE compounds are used for low friction or backup ring functions.
| Material | Common Shore Hardness | Typical Working Range | Notes |
|---|---|---|---|
| NBR | 70 to 90 Shore A | -30 °C to +100 °C | Good with air and mineral oil. Limited ozone and polar solvent resistance. |
| Polyurethane (TPU) | 85 to 95 Shore A | -30 °C to +80 °C | High wear resistance and low friction. Some grades are sensitive to hot water and steam. |
| FKM | 75 to 90 Shore A | -20 °C to +200 °C | Better high temperature and chemical resistance. Higher material cost. |
| HNBR | 70 to 90 Shore A | -30 °C to +150 °C | Better heat, ozone, and wear resistance than NBR. |
| Filled PTFE | Shore D scale for most compounds | -200 °C to +260 °C | Low friction. Used for backup rings and special low friction seals. Low elasticity. |
These material values are general reference ranges. The final temperature resistance and chemical compatibility depend on the specific compound, seal profile, groove design, and operating environment. Always confirm with the material datasheet.
EPDM and silicone are less common for dynamic pneumatic cylinder seals. EPDM has limited mineral oil compatibility. Silicone has lower tear strength and poor wear resistance in many dynamic applications.
Pneumatic cylinder seal selection starts with cylinder bore diameter, rod diameter, and groove dimensions. The groove bottom diameter, groove width, radial clearance, and installed seal cross section must be checked together. A seal may have the correct ID and OD but still leak if the groove is wrong.
Check bore and rod surface finish, rod runout, and seal groove edges. A worn rod or rough bore can destroy a new pneumatic cylinder seal quickly. The seal must slide over a clean surface without cutting the lip or pulling the ring out of the groove.
Common pneumatic cylinder standards include ISO 15552, ISO 6432, and ISO 21287. These standards define bore and rod sizes for many industrial air cylinders. Some equipment may use inch dimensions or manufacturer specific sizes. When the cylinder has no standard mark, measure the bore, rod, groove, and installed seal directly.
Use the ID, OD, width format carefully. The measuring order changes by seal type and supplier. For an O-ring, the key dimensions are inside diameter and cross section. For a piston seal, the key dimensions are piston groove bottom, bore diameter, groove width, and seal height. For a rod seal, check rod diameter, housing bore, groove depth, and groove width.
Seal replacement should correct the root cause. If the new seal runs in the same bad conditions, the new seal will also fail early. Common causes of pneumatic cylinder seal failure include the following conditions.
Air quality matters. Moisture, oil mist, and small particles can change seal life. A maintenance team should check the air filter, regulator, and lubricator settings when pneumatic cylinder seals fail repeatedly.
CORASEALS can quote individual pneumatic cylinder seals or a complete pneumatic cylinder seal kit. The quotation requires the same dimensional and operating information regardless of whether the order is for one seal or a full kit.
For a pneumatic cylinder seal kit, provide the cylinder manufacturer, model, bore diameter, rod diameter, and a drawing or photo if available. If the cylinder is obsolete or custom, provide the groove dimensions and the position of each seal. Do not send only a part number because the same part number can refer to different profiles in different catalogs.
Use the following list when you prepare a quotation request for CORASEALS.
Send the cylinder bore diameter, rod diameter, groove dimensions, operating pressure, temperature, air quality, lubrication, seal profile, material, and required quantity. Include a drawing, sample photo, or existing seal part number when available. Contact CORASEALS through the website quotation form for pneumatic cylinder seal pricing.
A piston seal seals the gap between the piston outside diameter and the cylinder bore. A rod seal seals the gap between the cylinder head and the moving piston rod. They have different directions of pressure and different wear surfaces.
NBR O-rings can work in many light duty pneumatic cylinders when the temperature, lubrication, groove design, and surface finish are within the NBR material limits. For high cycle rates or high wear conditions, a polyurethane U-cup or lip seal often performs better.
Measure the cylinder bore, rod diame
