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  #31  
Old 03-22-2013
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Re: Send packing the stuffing gland..

Quote:
Originally Posted by fallard View Post
The only o-rings in my PSS shaft seal are on the rotor, which is fixed to the shaft. There isn't any maintenance that I feel is necessary here. You could check with PYI to get there opinion on routine maintenance.

I replaced my bellows when they were about 18 years old. They seemed stiff to me, but there weren't any drips, so it was purely precautionary. PYI advised me that this was the right approach. The newer bellows use a different material.

My dripless shaft seal has performed flawlessly for 22 years. I do not have the tube for water lubrication, which makes more sense on a power boat running longer and at higher revs. My seal gets lubricated by whatever water gets thru the cutless bearing.

I've wondered about a catastrophic failure but, should the seal or bellows blow out, it seems highly unlikely that enough water would flow past the cutless bearing to overwhelm a bilge pump. I'm fairly certain I could keep up with it using the manual backup bilge pump in my cockpit.

I have read the above with great intrest many thanks for the posting.

I guess there may well be something one could use as an emergency in the event of a failure. Like denzo tape or something... at least it will buy some time .

Comments welcome on what one could use.
Robert
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  #32  
Old 03-22-2013
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Re: Send packing the stuffing gland..

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Originally Posted by macwester26 View Post
I intend to use a dedicated sea **** just to supply the raw water to the pss seal or another type of seal.

Just a strait forward sea **** with a grp ( home made ) water scoop fitted to the outside of the fitting.

So even when the engine is NOT running just sailing along will still permit water to go through the fitting.

Robert
You probably don't need to go to such lengths. It is pretty simple. The water flows up the stern tube by gravity, into the bellows and bathes the inside of the carbon seal. This is enough to lubricate and cool the seal, which generates almost no friction. The only reason for the tube is to allow any air that might get trapped in the bellows to escape. This tube was not on earlier models as I understand. No seacock, scoop, or dedicated pump necessary.

Here is a picture of mine before I put the tube on. The tube just goes up vertically about two feet where it is secured with two cable ties to an existing bracket. And that's all you need.
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  #33  
Old 03-22-2013
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Re: Send packing the stuffing gland..

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Originally Posted by johnnyquest37 View Post
If set up as a vent hose as the manufacturer suggests for sailboats, it could allow for water in the boat if not done properly or if the vent hose fails for some reason.
True. I just add that to the list of the other five thru hulls that keep me up at night
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  #34  
Old 03-22-2013
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Re: Send packing the stuffing gland..

Thanks for the posting.

I am learning more and more about theses seals with every post.
I have allways used stuffing glands in the past and thought this time i would try some other type of seal.
Many thanks

Robert
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  #35  
Old 03-22-2013
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Re: Send packing the stuffing gland..

The PSS seal is based on a graphite-to-stainless contact. The graphite is in the form of a "donut" that is attached to a polymer bellows that is compressed about 3/4". The bellows acts like a spring to keep the graphite "donut" pressed against a highly polished stainless steel rotor. The rotor is a tight fit to the shaft and includes 2 o-rings to assure no water leaks past the rotor where it contacts the shaft.

Graphite is an inherent "lubricant", so I'm not sure what the water does--other than perhaps providing cooling to keep the rotor from getting hot. The design of the seal is such that the graphite-stainless interface is dry and does not normally see water. If that were the case, the "dripless" shaft seal would drip.

Final note: I replaced by bellows and o-rings, but the graphite stator and the SS rotor are entering their 23rd year of service, with no end in sight. I would not worry about water circulation to the seal on a sailboat.
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Old 03-22-2013
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Re: Send packing the stuffing gland..

The traditional stuffing box is just not such a big deal. After 20 years, we replaced the stuffing material while the boat was in the water....worked fine and the new packing material is working fine. Hand tightened the packing nut to tune the drip rate. There are many other major projects you can do to "improve the boat". BTW, the boat was in the water at the time when we did this.
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  #37  
Old 03-22-2013
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Re: Send packing the stuffing gland..

We've got a PSS -- it was there when we bought the boat, and there's no record of when it was installed. But I think I'm safe in assuming that it's at least 15 years old.

Right now, it's sitting in a shoebox in my garage. When I get the engine and prop shaft reinstalled, the PSS will be going back on. That said, I will replace the rubber bits and the grub screws. They still look to be in OK shape, but it seems prudent to replace them while I've got it all off the boat now.

After getting it apart, I saw that there's no way I'll ever generate enough wear on the graphite seal for that to become a worry.

I did find a little bit of pitting on the face of the s/s rotor. I've still got to lap the face back to a mirror finish, but that's gonna have to wait for a while yet.

Another prudent step (as MaineSail recommends) is adding a shaft collar immediately forward of the s/s rotor as an added safety measure in case the grub screws lose their grip on the shaft.

About the O-rings -- the only time they move on the shaft is during installation. After that they simply sit there stationary to keep the water out, i.e. the shaft does not rotate in relation to the O-rings. The only wear in the assembly is between the s/s rotor and the graphite donut.
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Last edited by PorFin; 03-22-2013 at 11:45 PM.
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  #38  
Old 03-23-2013
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Re: Send packing the stuffing gland..

Before you think I'm down on these, I do have a dripless seal on my current boat and spec-ed it when it was built.

One boat back I did have one fail underway. I was under power and had a bilge alarm go off. Investigating I found that the donut had shifted forward on the shaft, causing the bellows to under compress. This allowed water to escape. Looked like an old rotary lawn sprinkler as the shaft rotated. Was able to shut down, loosen the grub screw, and move the donut aft, compressing the bellows. Of course, on this particular boat the seal was located under a generator, following the basic rule of boats, if you really need to fix it, you cannot reach it easily.

Since then, I've put a zinc on the shaft, forward of the donut to serve as an emergency stopper for the donut. Belt and suspenders. The installation instructions about these donut set screws are very specific, and I think I remember you are only supposed to tighten them once or replace the screws (or something like that).

Nevertheless, off I went again and put it in my current boat. Counting backwards been using them since mid 1990's with only this one failure which was probably caused by bad installation or maintenance.
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  #39  
Old 03-23-2013
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Re: Send packing the stuffing gland..

Quote:
Originally Posted by capecodda View Post
Since then, I've put a zinc on the shaft, forward of the donut to serve as an emergency stopper for the donut. Belt and suspenders.
There are two set screws on the rotor that are intended to "bite" into the shaft to keep it in place. If they loosen, the bellows can push the rotor back on the shaft, thereby allowing water to leak through and be spun off as the shaft rotates--hence the lawn sprinkler comment.

In theory, the second set screw would back up the first set screw, but I like the idea of another backup. The shaft zinc would work if it can really be clamped down on the shaft. It might be a good idea to sand down the mating faces of the zinc to make sure you can really clamp down with enough force to assure it would stay in place.

Considering the actually force produced by the compressed bellows, it probably doesn't take much to back up the rotor, so that the unmodified zinc of the proper size is probably quite adequate. But if you really want peace of mind, make sure the zinc is clamped tight.
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Old 03-23-2013
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Re: Send packing the stuffing gland..

I had a PSS on my boat when I purchased it. It leaked, most likely because it wasn't installed properly. Even worse was the allen set screws in the collar were rounded out. So I had to cut the shaft out of the boat, not an easy feat on a Sabre 28. This has left me with a bad feeling about he PSS even though I know a lot of people are very happy with them. I just felt stuck with no way to stop the leak and the only fix was a 4" angle grinder with a cut off disc to get the shaft out. If you can't remove the collar you can't remove the shaft.

I switched to a regular stuffing box with Duramax Ultra-X stuffing. I feel safer knowing I have more flexibility of managing an issue with the standard stuffing box. I do all of work myself but I also think a PSS might be a bid too complicated for a regular mechanic that wants to get in an out.

I think it was Maine Sail who recommended using a collar from McMaster-Carr to backup the PSS collar for safety. It's a little cleaner than a zinc or the hose clamp that was on my shaft. McMaster-Carr

Just my opinion,
-Joe
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