Non-contact seals (e.g. gap seals) are not suitable for gases due to their lower viscosity unless they are combined appropriately with a liquid as a barrier medium (Figure S 73).
Depending on the design, the pressure in the barrier medium is either generated externally or using a centrifugal force. In the latter case, a further stationary seal, which should also have no friction, is required for sealing in the case of a stationary shaft.
The use of the barrier medium is also necessary where sliding ring seals are used to seal gases.
Figure S 73: Barrier medium seal