It is vitally important for all boats and marine craft to avoid letting water get into the engine parts, especially corrosive sea water. However, craft that use a conventional packing gland, or stuffing box, around the exit point of the propeller shaft experience a continuous water drip, which is actually necessary for lubrication. This problem can be eliminated by using the PSS dripless shaft seal, manufactured by PYI Inc.
A dripless marine shaft seal can use either lip seals or face seals to achieve the dry bilge. A lip seal is a rubber sleeve inside a metal housing, fitted over the shaft which rotates inside it. The problem with this is that it causes wear and tear on the shaft, as well as on itself.
The PSS (packless sealing system) from PYI Inc instead uses a face seal, in which a reinforced rubber bellows device is secured to a carbon graphite flange at one end, and to the shaft log at the other. The flange is forced by the bellows against a polished steel rotor mounted on the shaft, which rotates against the flange. Because both surfaces are highly polished, water cannot pass between them when one is rotating, even amidst heavy vibration from the engine.
Those who have used the PSS shaft seal from PYI Inc report that it brings considerable benefits compared with the old stuffing box. One of the biggest is that it is possible to “set and forget” – that is, once installed it is virtually maintenance free. This is largely due to the use of nitrile O-rings between the shaft and the rotor. Nitrile is an exceptionally durable material which is resistant to variations in temperature, and which unlike rubber will not be damaged by contact with petroleum products. O-rings are constructed as a seamless whole, not fused together, so are highly unlikely to come apart.
Most boat owners agree that the marine shaft seal from PYI Inc has virtually superseded the stuffing box. Many have reported six or more years of daily use with not even a drop of water entering the craft. With no shaft wear, no maintenance and no adjustment required, this does seem to be the seal of the future.