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PSS Type B Shaft Seal


For 4" to 6-1/2" (100mm to 150mm) shaft diameters


The Type B PSS Shaft Seal is a mechanical face seal. The sealing surface is created between the flat surfaces of the rotating stainless-steel rotor and the stationary carbon flange. The stationary carbon flange is attached to the front side of the bellow with hose clamps, and the back end of the bellow fits over the Stern tube and is secured with hose clamps. The stainless-steel rotor is fit on the shaft in front of the carbon flange. The stainless-steel rotor is used to compress the bellow before the rotor is secured to the shaft with set-screws. This compression (pre-load) maintains constant contact between the two flat faces of the stainless-steel rotor and carbon flange, allowing the PSS to compensate for the variable fore and aft movement due to propeller thrust. The carbon flange is over-bored to the shaft diameter allowing it to “float” around the shaft and thus compensate for most misalignment and vibration problems. The stainless-steel rotor is sealed to the shaft by two O-rings that are recessed into the bore of the collar. These O-rings rotate with the shaft and stainless-steel rotor and do not experience wear during operation.


Temperature Limits: -13°F to 425°F (-25°C to 220°C)
Pressure Limits: 50 PSI (3.5 BAR)
Shaft RPM Limits: 7,000 RPM
Carbon Graphite: Lapped to 4 HLB (0.000044" tolerance)
316SS / Nitronic 50: Faced to 9 Ra
Bellow Material: Mandrel formed silicone / fabric 








1 - This clamp assembly maintains the PSS Type B preload / compression without the need for set screws..

2 - A seal is created between the two flat surfaces of the carbon stator and the stainless steel rotor.

3 - Water is fed into the PSS Shaft Seal for cooling/lubricating the seal faces on high speed vessels.

4 - The stationary carbon stator is attached to the nitrile bellow, which is attached to the stern tube (shaft log).

5 - Stainless steel rings are fit to the bellow for increased strength, support and durability.

6 - Hose clamps secure the PSS Type B Shaft Seal to the stern tube and onto the carbon stator.

7 - Hose clamp tail protection, Clamp Jackets.






The rotor on the Type B seal is manufactured out of Nitronic 50 stainless alloy machined to a 9Ra finish on precision CNC lathes. It is secured on the shaft with large locking collar placed in front of the rotor. This collar (clamp) has a dual purpose: It secures the rotor in place on the shaft and is used as a tool during installation. As on all the PSS seal family, the carbon stator further polishes the rotor during the initial hours of operations. The Nitronic 50 material is a very high grade of stainless steel which is almost totally corrosion resistant. This rotor does not need replacement under normal operating conditions.





Carbon Stator

Carbon-graphite is a versatile mechanical seal face material when used with mating rings of harder material. The PSS carbon has superior wear characteristics and broad chemical resistance.

The high density, resin impregnated carbon stator is manufactured from a space age composite which is first mixed and molded, then formed under pressure. The blank parts are then baked, machined and lapped to a measured flatness of 4 helium light bands (measured at 0.000044" of variation over its entire lapped surface). The grade of carbon composite used in the PSS Shaft Seal has a maximum operating temperature of 500°F (+260°C) and cannot melt if the seal runs dry for a short period of time unlike a lip seal or a plastic face seal. The high density of the carbon greatly increases the longevity and wear resistance. Several commercial vessels have recorded over 40,000 (over 4-1/2 years of continuous operation) engine hours on the same, original components. The carbon should not need to be replaced under normal operating conditions.

The PSS Type B carbon stator is equipped with dual water injection ports for positive water supply to be plumbed in.








The bellow on both the PRO and Type B PSS seal is constructed out of high temp silicone laminated with either 4 or 5 plies of polyester fabric (aramid in larger sizes) and covered with a layer of fluorosilicone. In addition both ends of the bellow are sealed so no water can get in the polyester/Aramid fabric. The 4 or 5 fabric inlay provides excellent strength to abrasion and resistance to pressure without loading the silicone. On the larger models, the strength is greatly increased by the use of stainless steel hoops laid into the convolutions of the bellow.



Bellow Rings

The PSS Type B Shaft Seal uses metal rings around the bellow for added strength due to the high pressures that the seal may encounter.



Added Strength

The bellow is reinforced with multiple plies of aramid fabric.



Hose Barb

For high speed vessels (12+ knots), a positive water supply is required to be plumbed to the PSS Shaft Seal for the purpose of lubricating and cooling the seal faces. Please review the PSS Shaft Seal Installation Instructions for more information on pickup points for water supply. In most cases, a slow speed boat (less than 12 knots) that does not have a bearing the shaft log does not require positive water feed and can simply be vented. Ideally, the vent line will be run at least 2-3 feet above the water line and will be as close to the center line as possible. This will ensure the vent hose is never below the water line, even with significant heeling. PSS Shaft Seal Installation Instructions has more more details on venting the seal.












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