A small interface. A big job.

Where the seal happens

The polished stainless rotor turns with the propeller shaft. The carbon stator stays with the boat. Their flat faces meet to form the dynamic seal. This is the working interface you can see at the front of a PSS assembly.

It is a different arrangement from a lip seal, where the sealing edge runs directly against the shaft. With PSS, the shaft carries the rotor while the sealing work happens between the carbon and metal faces.

Why the bellows matters

The flexible bellows connects the stationary assembly to the stern tube. Its installed compression maintains pressure between the sealing faces while allowing for normal fore-and-aft shaft movement.

Think of the assembly as a system: bellows, faces, rotor retention and water supply each have a job. Correct shaft size alone cannot compensate for an installation with insufficient space or an incorrect setup.

The seal inside the rotor

Two O-rings sit inside the rotor and seal it to the shaft. Because the rotor and shaft turn together, these O-rings do not form a sliding sealing edge against a rotating shaft surface.

The distinction does not make shaft condition irrelevant. Correct diameter, sound O-ring contact areas, careful preparation and suitable alignment still matter. A refit is an opportunity to inspect the complete shaft installation.

Water belongs at the faces

The faces need water for cooling and lubrication. Depending on the vessel, the installation uses a suitable vent or a positive water feed. The correct arrangement is chosen from the current model-specific instructions.

A dry bilge and a water-lubricated seal are compatible ideas. The aim is to keep cooling water at the interface while preventing it from entering the boat through the seal.

Choose the complete assembly

Type A, PRO and Type B apply this face-seal principle to different shaft ranges and constructions. Start with measurements, then consider the vessel, access and service plan. Luxfords can help turn those details into a product enquiry.

• Find your exact shaft diameter.
• Measure the stern-tube outside diameter.
• Confirm room for the seal and future service.
• Ask Luxfords about the right family and water arrangement.