PSS Type A Dripless Mechanical Propeller Shaft Seal for 3/4" to 3" Shafts

PSS Type A Dripless Mechanical Propeller Shaft Seal for 3/4" to 3" Shafts

The PSS Type A Shaft Seal is a dripless mechanical face seal designed for marine propeller shaft installations. Unlike conventional stuffing boxes that use packing material, the PSS system creates a sealing interface between a rotating stainless steel rotor and a stationary carbon graphite flange.

The stainless steel rotor is mounted on the propeller shaft and secured with set screws. The carbon flange is attached to a flexible rubber bellows, which connects to the stern tube using hose clamps. Compression of the bellows maintains contact between the two sealing faces, creating a mechanical shaft seal.

The Type A range accommodates propeller shaft diameters from 3/4" to 3", with multiple stern tube connection sizes and installation dimensions. Each configuration is selected according to the shaft diameter and stern tube outside diameter.

Key Features

• Dripless mechanical sealing: Face seal design using a rotating stainless steel rotor and stationary carbon graphite flange.
• Packing-free construction: Does not require conventional stuffing box packing.
• Axial movement compensation: Bellows compression maintains sealing face contact during fore-and-aft shaft movement caused by propeller thrust.
• Misalignment and vibration accommodation: The carbon flange can float around the shaft to accommodate minor alignment variations.
• Stainless steel rotor: Precision-machined rotating sealing component.
• Carbon graphite stator: Stationary sealing face attached to the flexible bellows.
• Double O-ring sealing: Two recessed O-rings seal the rotor against the propeller shaft.
• Nitrile bellows: Molded flexible construction for the stern tube connection.
• Hose clamp attachment: Bellows secured to the stern tube and carbon flange.
• Water connection: Hose barb for supplying cooling and lubricating water where required.
• Wide size range: Shaft diameters from 3/4" to 3".

Technical Specifications

Size Groups and Installation Dimensions

The PSS Type A range is available with different rotor diameters, bellows compression requirements and stern cuff lengths. All dimensions below are in inches.

Mechanical Sealing System

The mechanical sealing interface is formed between two flat surfaces:

• Stationary Carbon Graphite Flange: Attached to the front of the flexible bellows.
• Rotating Stainless Steel Rotor: Mounted directly on the propeller shaft and secured with set screws.

When installed, the rotor compresses the bellows, applying a preload that maintains contact between the two sealing faces. This allows the mechanical seal to accommodate axial movement associated with propeller thrust.

The carbon flange is over-bored relative to the shaft, allowing limited floating movement to accommodate misalignment and vibration.

Rotor and O-Ring Sealing

The stainless steel rotor is secured to the shaft using set screws. Two O-rings recessed into the rotor bore provide a seal between the rotor and propeller shaft.

These O-rings rotate with the shaft and rotor rather than rubbing against a stationary shaft surface during normal operation.

Bellows and Stern Tube Connection

The molded nitrile bellows connects the carbon flange to the stern tube. Hose clamps secure the bellows at both ends.

The bellows provides the compression needed to maintain mechanical sealing face contact. Available stern cuff lengths are 1.5", 2" and 2.5", depending on the configuration.

Water Supply and Lubrication

The PSS shaft seal incorporates a hose connection for cooling and lubricating water. High-speed vessel installations require a positive water supply to the sealing faces.

Water supply and venting arrangements must be matched to the vessel's operating conditions and shaft seal installation.

Dimensions and Selection

Select the correct PSS Type A shaft seal using the following dimensions:

• A - Shaft Diameter: Propeller shaft diameter, from 3/4" to 3".
• B - Stern Tube Diameter: Outside diameter of the stern tube, selected from the applicable connection range.
• C - Uncompressed Length: Overall axial length before bellows compression.
• Approximate Compression: 3/4" or 1", depending on the selected model.
• D - Rotor Diameter: Outside diameter of the stainless steel rotor.
• E - Stern Cuff Length: Length of the stern tube connection section.

Several stern tube diameter ranges are available for each propeller shaft diameter. The uncompressed length may also differ between versions with the same shaft diameter.

Before ordering, verify the propeller shaft diameter, stern tube outside diameter, available installation space and the dimensional requirements of the selected article number.