Pneumatic seals are using compressed air to seal the gap of the rotating shaft without leaking the working medium. The annular groove is machined on the casing. And the gap of the rotating shaft is blocked by the compressed air to prevent leakage of lubricating oil.
The pneumatic seal has the characteristics of simple structure but requires a gas source with a certain pressure to supply gas. So the consumption of compressed air is large. And the pressure of the gas source is larger than the pressure of the sealing medium by 0.03~0.05Mpa. Pneumatic seals are not limited by speed and temperature. They are usually used for sealing of rotating machinery with small pressure difference. They are used for liquid medium sealing and also for gas medium sealing, such as to prevent leakage of lubricating oil in bearing housing. Sometimes used in combination with labyrinth seals or spiral seals.