PSS Type A Dripless Mechanical Propeller Shaft Seal for Ø20–60 mm Shafts

PSS Type A Dripless Mechanical Propeller Shaft Seal for Ø20–60 mm Shafts

The PSS Type A Dripless Mechanical Propeller Shaft Seal is a mechanical face sealing system designed for marine propulsion installations with metric propeller shafts. The seal operates through contact between a rotating stainless steel rotor and a stationary carbon graphite stator, providing a packing-free alternative to conventional stuffing box seals.

This range covers propeller shaft diameters from 20 to 60 mm, with imperial stern tube connections from 1 1/4" to 5". Different configurations are available to match the propeller shaft diameter, stern tube outside diameter and available installation space.

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

The sealing arrangement accommodates fore-and-aft shaft movement caused by propeller thrust. The carbon stator can also float around the shaft to compensate for minor misalignment and vibration.

Key Features

• Dripless mechanical face seal: Contact between a rotating stainless steel rotor and a stationary carbon graphite stator.
• Packing-free construction: No conventional stuffing box packing required.
• Metric shaft compatibility: Available for shaft diameters of 20, 22, 25, 28, 30, 32, 35, 38, 40, 45, 50, 55 and 60 mm.
• Imperial stern tube connections: Multiple nominal sizes from 1 1/4" to 5".
• Carbon graphite stator: Stationary sealing face attached to the flexible bellows.
• Stainless steel rotor: Rotating sealing component secured to the shaft with set screws.
• Dual O-rings: Seal the rotor against the propeller shaft.
• Molded nitrile bellows: Provides axial compression to maintain sealing face contact.
• Axial movement compensation: Accommodates shaft movement associated with propeller thrust.
• Misalignment accommodation: Floating carbon stator allows limited movement around the shaft.
• Water connection: Hose barb for cooling and lubrication water.

Technical Specifications

Available Shaft Sizes and Rotor Dimensions

The rotor diameter, bellows compression and stern cuff length vary according to the selected shaft size. All dimensions other than shaft diameter are expressed in inches.

Stern Tube Compatibility

Each PSS Type A seal is selected according to both the metric propeller shaft diameter and the imperial stern tube outside diameter. The following nominal stern tube sizes are available within the listed range:

The nominal stern tube size identifies the connection version. The compatible outside diameter range extends from the nominal dimension to 1/8" above it.

Mechanical Face Sealing System

The PSS Type A seal operates through contact between a stationary carbon graphite stator and a rotating stainless steel rotor.

The rotor is installed on the propeller shaft and compresses the bellows before being secured with set screws. This compression creates the preload required to maintain sealing face contact during operation and accommodates axial shaft movement caused by propeller thrust.

The carbon stator has an oversized central bore, allowing it to float around the propeller shaft and accommodate minor misalignment and vibration.

Stainless Steel Rotor and O-Rings

The stainless steel rotor provides the rotating sealing surface and is secured to the shaft using set screws. Two recessed O-rings seal the rotor against the shaft.

The O-rings rotate together with the rotor and propeller shaft instead of sliding against the shaft surface during normal operation.

Carbon Graphite Stator

The stationary carbon graphite stator provides the non-rotating sealing surface of the mechanical assembly. Its lapped face contacts the stainless steel rotor to create the shaft seal.

The stator is connected to the flexible bellows, which maintains sealing pressure through axial compression.

Molded Nitrile Bellows

The Type A bellows is manufactured from molded nitrile material and connects the stationary carbon stator to the stern tube. Hose clamps secure the assembly to the stern tube connection.

Depending on the selected model, the approximate bellows compression is 3/4" or 1", while the stern cuff length is 1.5", 2" or 2.5".

Water Supply and Cooling

The PSS Type A seal includes a water connection for cooling and lubrication of the mechanical sealing faces.

For vessels operating at speeds of 12 knots or higher, a positive water supply is required. Lower-speed installations require an appropriate water supply or venting arrangement.

Dimensions and Selection

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

• A - Propeller Shaft Diameter: Metric shaft diameter from 20 to 60 mm.
• B - Stern Tube Diameter: Compatible outside diameter of the stern tube, expressed in inches.
• C - Approximate Length: Overall axial length before bellows compression.
• Approximate Compression: Required bellows compression, 3/4" or 1" depending on model.
• D - Rotor Diameter: Outside diameter of the stainless steel rotor.
• E - Stern Cuff Length: Length of the stern tube connection section.

Before ordering, verify the metric propeller shaft diameter, stern tube outside diameter and available installation space. The correct combination of shaft diameter and stern tube size determines the appropriate article number.