The Airspace Non-Pollution Stern Tube Seal
The Airspace Non-Pollution stern tube seal has shown that environmental and technical operations considerations are not mutually exclusive. From the technical and ecological point of view a safe sterntube system is becoming increasingly important for ship operators. These requirements have led to the development of the “Simplex-Compact Airspace Non-Pollution” sterntube seal.
The oil and water are separated by an air chamber filled with compressed air so that oil leakage out of the sterntube into the surrounding seawater or ingress of seawater into the sterntube is now technically impossible. The oil and water necessary for lubricating the sealing rings is collected in the separating chamber and automatically drained into the bilge at periodic intervals by a pipe and valve system. “Non-Pollution” means: No seawater enters the sterntube oil, and no contamination of the seawater by sterntube oil.
A water-free sterntube bearing guarantees a long service life for the bearing with all the associated benefits. Failure of the very important propeller shaft bearing has become virtually impossible. With the “Simplex-Compact Airspace Seal”, in addition to the environmental aspect, ship operators no longer have to be concerned that they will become involved in extensive and costly liability proceedings with port authorities. The ship operator can now state that the propeller shaft seal cannot be the cause of any oil pollution.
The Airspace System
The sealing rings are arranged so that three outer rings face the sea water and the innermost ring #3 faces the sterntube oil. Sealing ring #0 serves mainly as a dirt rejector and sealing ring #1 seals against the sea water. Using a circulator in chamber I, cooling of sealing ring #1 is achieved by constant circulation of the surrounding outside water through the chamber. Located between sealing ring #1 and #2, the airfilled chamber II (Airspace) is connected to an air supply to form a defined pressure cushion and a drainage inboard. Chamber III which is between sealing ring #2 and #3 is filled with oil. The oil pressure in chamber III is determined by the installation height of the oil tank which is connected to the chamber by a pipeline.
Free fluid particles are collected in the Airspace chamber and are blown and drained inboard at predetermined, adjustable intervals by the pneumatic automatic control system. For vessels which have large differences in draft between load and ballast conditions, the pneumatic control has an additional input signal from a draft meter.
The Airspace Advantages:
- Two seals in one: the non-pollution Airspace Stern Tube Seal and the SC 2 B standard seal.
- Low air consumption – no constant bubbling
- Airspace pressure is always lower than the water pressure: air cannot escape with oil to the seawater.
- Condition Based Monitoring of the sealing rings using the drain test feature.