The aft stern tube seal is a multi-barrier lip type seal which contains four seal rings running on a seal liner, to
prevent grooving of the shaft. The two seal rings face the stern tube towards the oil, providing an active double security against oil spills. The other two seal rings face towards the seawater to effectively seal against seawater and sediments.
The pressurised air in the central void space is dynamically controlled and monitored, based on the variations of the seawater pressure, which keeps the Wärtsilä Airguard system continuously pressure balanced.
This results in less pressure and load on the four seal rings, and minimal wear on the liner. As an additional
safety feature, a specially designed P-ring protects the seal ring from being damaged by fishing nets and lines.