Pneumatic seals: how they differ from hydraulics
A pneumatic cylinder looks like a small hydraulic cylinder, but it works very differently. Here is why dedicated seals are needed and how to choose them.
Pneumatic cylinders and actuators are present in almost every automated plant: packaging lines, wrapping machines, light presses, pick-and-place systems, automatic doors. At first sight they look like hydraulic cylinders, but compressed air has very different characteristics from oil, and this completely changes the requirements for seals.
The main differences
Lower pressures
Working pressures in pneumatics are much lower than in hydraulics. Seals therefore do not need to withstand high forces, but they must seal well even at low pressure, which requires sensitive lips and good preload.
Friction and smooth running
Air does not lubricate like oil. In many modern plants the air is dry and unlubricated, so seals must work with a film of grease applied during assembly. That is why friction is a key parameter: high friction causes jerky movement, higher air consumption and rapid wear.
High speeds
Pneumatic cylinders often move very quickly and perform a very high number of cycles. Seals must withstand the heat generated and keep sealing over time.
Compressibility of air
Air is compressible: small leaks mean loss of force, imprecise movement and compressor energy consumption. Good sealing pays off on the energy bill too.
Types of pneumatic seals
- Rod seals: often combine sealing and wiping in a single element, protecting the cylinder from dust in a compact space.
- Piston seals: single lip profiles fitted in pairs, or bidirectional seals and complete pistons with integrated seals.
- Cushioning seals: they slow the piston at the end of stroke to reduce shocks and noise.
- O-rings and static seals: for end caps, fittings and valves.
- Guide rings: often in POM or low-friction engineering materials.
In our catalogue you will find a section dedicated to pneumatics, with rod and piston seals in various profiles and sizes.
The most used materials
- NBR: widespread and versatile, good for most standard applications.
- Polyurethane: excellent wear resistance and long life, much appreciated for rods and pistons.
- FKM: for high temperatures.
- Special low-friction materials: for very slow or precise movements.
Tips for a long life
- Air quality: filters and condensate separators protect seals from water, degraded oil and particles.
- Lubrication during assembly: use grease compatible with the seal material. If the system is lubricated, always keep using the same type of oil.
- Alignment: side loads and misalignment quickly wear guides and seals.
- Adjusted cushioning: end-of-stroke impacts damage the piston and end caps.
- Complete kits: replace all the seals of the cylinder, not just the one that leaks.
Identifying the right seals
As with hydraulics, the most important thing is the dimensions: rod diameter, bore, groove sizes. With the search by dimensions on our website you will quickly find compatible profiles. If the cylinder is branded and you cannot find the original kit, send us dimensions and photos: we will show you the available alternatives.
Frequently asked questions
Can I use hydraulic seals in a pneumatic cylinder?
It is usually not recommended: hydraulic seals have preloads and friction designed for oil and, with air, they can cause jerky movement and premature wear.
Which grease should I use for assembly?
A grease specific to pneumatics, compatible with the seal material. Avoid generic greases that can make the elastomer swell or harden.
Why does the cylinder jerk at low speed?
It is often stick-slip caused by high friction or insufficient lubrication. Low-friction seals and correct greasing solve most cases.
