The Wärtsilä Airguard seal works with compressed air, which is applied to the void space between the seal rings. This constant flow of compressed air into the void space is automatically set higher than the seawater pressure, resulting in a small amount of air forced out into the seawater.
The void space is connected to an inboard drain collection system. Any seawater or oil that infiltrates the void space is automatically drained inboard, preventing oil leaking outboard or seawater entering the stern tube. As the Wärtsilä Airguard seal successfully takes away the oil-to-sea interface, it can be operated with mineral oil in accordance with the 2013 Vessel General Permit.