Dripless Shaft Seal versus Stuffing Box - Page 7 - SailNet Community

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  #61  
Old 12-29-2012
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Re: Dripless Shaft Seal versus Stuffing Box

I too have had that same discussion with Mr Gerry Douglas of Catalina and the sales manager of PSS about their dripless system. What Mr Douglas relayed to me was failure of the bellows due to overheating when there is no water in the shaft tube to cool down the bellow while the shaft is turning. This lack of water can come from a launch of vessel, air bubble getting into the shaft and creating a air lock or obstruction getting into the shaft log and not letting in water (think crap pot lines, fishing line, etc.). The sales manager confirmed this problem with me and demonstrated it at the Ft Lauderdale boat show last year.
There is a big difference between power boat vs sailboat applications due the difference in RPM's the shaft turns. The PSS dripless system likes higher RPM's vs slow RPM's of sailboat shafts. Furthermore, how some folks think that slow RPM's (1800-2200) on their diesels are good for it (another subject another thread) hence even slower rotation on the shaft. This is where the vent tube comes into play. Careful installation is required here as well as the set screws. If the tube blocks up in any way the bellows can overheat as well.
BTW I have the PSS system on my current boat. It has worked flawless in over 4 years. What I don't like and it makes me nervous is when I move the shaft out of alignment by hand or foot I get water out. I was told this is normal. Not so sure about that.
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  #62  
Old 12-31-2012
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Re: Dripless Shaft Seal versus Stuffing Box

Quote:
Originally Posted by billyruffn View Post
There's nothing "wrong" with the PSS shaft seal -- you just have to know how to use it --- like so many other things on a sailboat. I've had the PSS shaft seal on BR for over 10 years with no problems.

Sailors, like astronauts, have to do things the right way. The use of the set screws is one the things you have to get right if you use the PSS SS. It's not rocket science -- you just have to read and follow the directions.

I appreciate your desire for robust gear, but that said: if you want to abuse the gear on your boat, go ahead. If you want to install it incorrectly, that's your call. If you want to use it to failure, be my guest. But I wouldn't be surprised if you were one day the victim of multiple, minor but progressive component failures that leads ultimately to catastrophy.

MaineSailor knows of what he speaks. The only thing I didn't see in his excellent post was the mention of use of Loctite thread locker on the second (outer) of the two lock screws. You shouldn't use it on the inner set screw because some of it might leak between the shaft and the collar making the collar very difficult to remove. That's another common mistake made by the inexperienced 18 year olds that work in boat yards (you know, the ones that flunked out of sub school). But, you'd know that, if you read the directions.

PS -- I spent a few years in the Navy, and IMO the 18 year old on a Navy submarine is a highly trained individual regardless of his rate.

PPS -- one of the things that I do to alert me to any movement of either the rubber compression collar and the SS ring-around-the-shaft is to make marks with a black magic market on the stern tube where the rubber compression collar meets the stern tube and where the SS ring-around-the-shaft meets the shaft. If either of these marks disappears then I know something is moving and needs attention. I have a look at these marks every day during my pre-start checks of the engine space.
Sorry you do not recognize a little sarcasm, little hard to convey maybe on the internet. My point is that no matter how smart and skilled an 18 year old is, there are certain things only experience will teach you. Don't worry about me abusing my equipment, I don't, but I design and build so if I do, it will keep going. Never had a failure yet, but then again I keep an eye on things, and being a licensed mechanical engineer with many years of hands on experience in designing, building, testing and maintaining anything from a hydro-electric plants to a submarines help. The navy would never have a little plastic hose fitting holding back the sea.
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