System pressure, sliding speed, temperature, media, surface roughness and system tolerances are the important parameters when choosing the type of the pneumatic sealing element.
The pressure does not go beyond 16 bar (special applications only) in pneumatic systems. That is why the pressure source (air compressors, etc) settings are between 3 to 8 bar. The expectation from the pneumatic sealing element is to function properly with no interruption in low pressures..
Pneumatic systems increasingly being used in automation processes and requires high sliding speed. The speeds (0.5 m/sec and higher) are generally higher than the hydraulic applications and these are named medium speeds in pneumatics. The negative effects of the friction forces cause by high sliding speed should be taken into consideration when choosing the material and profile to have the optimum sealing in the system
Operating temperature and local temperature increasement due to the friction forces should be taken into consideration when choosing the sealing elements in pneumatic systems. For high temperature applications sealing elements can be used from PTFE and FKM.
Generally, the compressed air contains dust, dirt and moisture if no prior operation is applied on it. Life span of the sealing element shortens under this operating condition. That is why filters should be used in order to purify the air from the compressor oil and to clean the air. Maximum cleanliness is essential before greasing and commissioning; the system must be completely free from machining residue, old lubricants and any other contaminations. Prepared compressed air should be used as dried or conditioned with special lubricants. Special assembly grease should be used for the sealing elements that will be working in non oiled systems in order to have optimum friction forces.