Pneumatic Seals for Air Cylinders, Valves and Actuators

Compressed air is a poor lubricant, and it can carry moisture, oil mist, rust and dust. Pneumatic seals must therefore run with low breakaway friction and remain flexible, often relying on grease applied at assembly and on a thin film of oil from the air line lubricator, if one is fitted. Many modern cylinders are "lubricated for life" and use specific greases and compounds, so changing lubrication practice mid-life can cause problems.

Pneumatic pressures are typically lower than hydraulic pressures, so extrusion is less of a concern, but speed can be high and cycle counts large. Seal wear, grease loss and contamination are the usual failure routes. For oil-based systems operating at higher pressure, see Hydraulic Seals. Where you only need to replace a groove ring, see Metric O-rings.

Piston seals

Double-acting cylinders use a symmetrical lip seal, a cup seal pair or a compact seal in one groove. Single-acting designs may use a one-way lip. Magnetic cylinders often combine a seal with a magnet ring and wear band.

Rod seals and rod wipers

A lip seal on the rod holds pressure, and a wiper excludes dust. Combined rod seals with an integral wiper exist where space is limited. See Wiper and Scraper Seals.

Cushion seals

Seals in the end-of-stroke cushion allow air to be restricted in one direction and released in the other, so the piston slows before impact.

Spool and valve seals

O-rings or lip-type seals that move in valve bodies. Low friction and swell resistance are important for reliable shifting.

End-cap and static seals

O-rings or moulded gaskets between cylinder tube and head. Often undersized or damaged by tube distortion.

Wear bands and guide rings

Carry side load on the piston and rod. See Wear Rings and Guide Rings.

The notes are typical and general. Always confirm against the manufacturer's data, including grease and fluid compatibility.

• NBR: the usual compound for general air service. Good wear resistance, but ozone and sunlight shorten life. Low-temperature grades are available.
• Polyurethane: excellent wear resistance for rod and piston seals, but can be less flexible at low temperature and may be damaged by hot, humid air in some grades.
• FKM: chosen for higher temperatures, and where aggressive lubricants are present. Stiffer at low temperature, so less suited to cold start-up with dry air.
• EPDM: used for systems with non-mineral lubricants or brake-type fluids. It is not compatible with mineral oil and swells in contact with it, so never use it in a lubricated system without checking.
• PTFE-based: low friction for non-lubricated cylinders and high-cycle applications, typically with elastomer energisers.
• Silicone: sometimes used in food-adjacent or low-temperature air equipment; mechanical strength is limited in dynamic use.

1. Identify the cylinder. Make, model and bore usually determine the seal kit. Many pneumatic cylinders follow dimensional standards, which makes interchange simpler than in hydraulics.
2. Measure the bore and rod diameters, and the groove geometry for non-standard cylinders. See our measuring guide, which applies the same principles.
3. Establish lubrication. Lubricated or non-lubricated systems need different compounds and greases.
4. State operating pressure, stroke speed and temperature, including cold storage or hot-process locations.
5. Consider the environment: washdown, abrasive dust, welding spatter or chemical vapour.
6. Decide kit or individual seals. A kit makes sense for planned servicing.

Compressed air used in food-contact, pharmaceutical or breathing-air applications requires technical review and the correct certification documents.

• Cylinder make, model and any code on the tube or end cap
• Bore, rod diameter and stroke
• Existing seal markings or part numbers
• Operating pressure and cycle rate
• Lubricated or non-lubricated air
• Environment: temperature, washdown, dust or chemicals
• Photos of the seals, piston and rod, plus quantity

Genuine pneumatic seals and kits are made by the cylinder manufacturer or by seal makers named in the cylinder documentation. Compatible seals follow the same dimensions and are made by other suppliers; they are often an economic choice for standard bore sizes. Verify the compound, lip geometry and grease, because different formulations affect friction and life. For ISO-style standard cylinders, interchange is usually more straightforward than for proprietary designs.

You can enquire about genuine or compatible replacement parts for pneumatic equipment from manufacturers such as Camozzi, Technimex and others. Supply route is confirmed when you enquire.

Pneumatic seals are often bought as kits for a known cylinder, so identification matters.

• Buy online: where a product is listed in the online shop with a confirmed price, you can order directly. Products are being added to the shop progressively, so not every item will be listed yet.
• Request a quote: for custom, bulk, unpriced or repeat-order requirements, send us a quote request with your details.
• Technical review: if you cannot identify the part, or the application is demanding, use Find My Seal or upload a drawing and our team will review it with you.

You can also call head office in Johannesburg on 011 079 6033, or WhatsApp 079 508 0989, or email info@globseals.com.

These guides support identification and compound choice.

• How to measure a hydraulic seal: measuring principles for rod and piston seals that apply to air cylinders
• NBR, EPDM, FKM and silicone comparison: which elastomers suit mineral-oil mist and which do not
• Common causes of seal failure: spotting dry-running, contamination and swelling failures